Methods for preparing buffers

WEBVTT
Kind: captions
Language: en

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- [Instructor] Let's look
at two different methods

00:00:01.930 --> 00:00:04.890
for preparing buffer solutions.

00:00:04.890 --> 00:00:05.820
In the first method,

00:00:05.820 --> 00:00:07.400
we're gonna add an aqueous solution

00:00:07.400 --> 00:00:09.660
of a strong base, sodium hydroxide,

00:00:09.660 --> 00:00:13.240
to an aqueous solution of
a weak acid, acetic acid.

00:00:13.240 --> 00:00:16.130
Our goal is to calculate the
pH of the buffer solution

00:00:16.130 --> 00:00:20.500
that forms when we mix these
two aqueous solutions together.

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Our first step is to
figure out how many moles

00:00:22.870 --> 00:00:25.060
of acetic acid that we have.

00:00:25.060 --> 00:00:28.530
So if we have 100 milliliters
of a 1.00 molar solution

00:00:28.530 --> 00:00:31.040
of acetic acid, we can use the equation:

00:00:31.040 --> 00:00:34.420
molarity is equal to
moles divided by liters

00:00:34.420 --> 00:00:37.010
to figure out the moles of acetic acid.

00:00:37.010 --> 00:00:40.530
Since the concentration is 1.00 molar

00:00:40.530 --> 00:00:42.990
and the volume is 100 milliliters,

00:00:42.990 --> 00:00:46.910
which is equal to 0.100 liters,

00:00:46.910 --> 00:00:51.833
x is equal to 0.100 moles of acetic acid.

00:00:52.800 --> 00:00:54.640
We can do a similar calculation

00:00:54.640 --> 00:00:57.890
to determine the moles of strong base.

00:00:57.890 --> 00:01:00.310
So for our aqueous solution
of sodium hydroxide,

00:01:00.310 --> 00:01:02.070
we have 50 milliliters of it

00:01:02.070 --> 00:01:05.130
at a concentration of 1.00 molar.

00:01:05.130 --> 00:01:08.560
So we plug in the concentration 1.00 molar

00:01:08.560 --> 00:01:10.520
into the equation for molarity,

00:01:10.520 --> 00:01:12.260
and we plug in the volume,

00:01:12.260 --> 00:01:15.870
and 50 milliliters is
equal to 0.050 liters.

00:01:15.870 --> 00:01:17.060
So solving for x,

00:01:17.060 --> 00:01:22.060
we find the x is equal to 0.050
moles of sodium hydroxide.

00:01:22.920 --> 00:01:25.370
Since sodium hydroxide is a strong base,

00:01:25.370 --> 00:01:28.500
it dissociates completely in solution.

00:01:28.500 --> 00:01:32.650
Therefore, if we have 0.050
moles of sodium hydroxide,

00:01:32.650 --> 00:01:37.020
we also have 0.050 moles of
sodium cations in solution

00:01:37.020 --> 00:01:40.780
and also hydroxide anions in solution.

00:01:40.780 --> 00:01:42.970
When these two aqueous
solutions are mixed,

00:01:42.970 --> 00:01:46.470
we're mixing 100 milliliters
with 50 milliliters

00:01:46.470 --> 00:01:50.820
for a total volume of 150 milliliters.

00:01:50.820 --> 00:01:51.653
Let me just go ahead

00:01:51.653 --> 00:01:53.150
and write that down here really quickly.

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And when the two solutions are mixed,

00:01:55.560 --> 00:01:59.270
the acetic acid will react
with hydroxide anions

00:01:59.270 --> 00:02:02.730
to form the acetate anion and water.

00:02:02.730 --> 00:02:04.170
To figure out what's left over

00:02:04.170 --> 00:02:06.200
after the reaction goes to completion,

00:02:06.200 --> 00:02:08.150
we're gonna use an ICF table,

00:02:08.150 --> 00:02:10.410
where I stands for initial,

00:02:10.410 --> 00:02:13.810
C is for change, and F is for final.

00:02:13.810 --> 00:02:16.270
We've already calculated
the initial number of moles

00:02:16.270 --> 00:02:20.420
of acetic acid is equal to 0.100,

00:02:20.420 --> 00:02:23.630
and the initial number of
moles of hydroxide anions

00:02:23.630 --> 00:02:26.660
is equal to 0.050.

00:02:26.660 --> 00:02:29.360
And if we assume the
reaction hasn't happened yet,

00:02:29.360 --> 00:02:32.180
the initial number of
moles of the acetate anion

00:02:32.180 --> 00:02:34.170
would be zero.

00:02:34.170 --> 00:02:35.080
For this reaction,

00:02:35.080 --> 00:02:38.340
the hydroxide anion is
the limiting reactant.

00:02:38.340 --> 00:02:41.330
And therefore, we're gonna
use it all up in the reaction.

00:02:41.330 --> 00:02:46.330
So we write -0.050 under
hydroxide in our ICF table.

00:02:48.440 --> 00:02:49.840
Looking at the balanced equation,

00:02:49.840 --> 00:02:53.080
the mole ratio of a acetic
acid to hydroxide anion

00:02:53.080 --> 00:02:54.570
is one-to-one.

00:02:54.570 --> 00:02:59.570
Therefore, if we are losing
0.050 moles of hydroxide anions,

00:02:59.620 --> 00:03:04.620
we're also losing 0.050
moles of acetic acid.

00:03:05.310 --> 00:03:07.600
So when the reaction goes to completion,

00:03:07.600 --> 00:03:10.550
all of the hydroxide
anions have been used up.

00:03:10.550 --> 00:03:14.610
Therefore, we have zero moles
of hydroxide anions left over.

00:03:14.610 --> 00:03:17.920
For a acetic acid, if
we started with 0.100

00:03:17.920 --> 00:03:20.680
and we're losing 0.050,

00:03:20.680 --> 00:03:23.380
half of the acetic acid
has been neutralized

00:03:23.380 --> 00:03:25.150
by the hydroxide anions,

00:03:25.150 --> 00:03:29.340
and we're left with 0.050 moles

00:03:29.340 --> 00:03:32.200
when the reaction goes to completion.

00:03:32.200 --> 00:03:33.650
For the acetate anion,

00:03:33.650 --> 00:03:36.690
the coefficient in the
balanced equation is a one.

00:03:36.690 --> 00:03:39.730
Therefore, if we're losing 0.050

00:03:39.730 --> 00:03:41.210
on the left side of the equation,

00:03:41.210 --> 00:03:46.210
we're gonna be gaining
0.050 on the right side.

00:03:46.320 --> 00:03:49.230
So when the reaction goes to completion,

00:03:49.230 --> 00:03:54.230
we have 0.050 moles of the acetate anion.

00:03:54.950 --> 00:03:57.540
A buffer solution consists
of significant amounts

00:03:57.540 --> 00:03:59.990
of a weak acid and its conjugate base.

00:03:59.990 --> 00:04:04.400
Acetic acid is a weak acid
and its conjugate base

00:04:04.400 --> 00:04:06.660
is the acetate anion.

00:04:06.660 --> 00:04:10.420
Therefore, the addition of
the strong base, hydroxide,

00:04:10.420 --> 00:04:13.150
which neutralized half of the acetic acid

00:04:13.150 --> 00:04:15.060
created a buffer solution

00:04:15.060 --> 00:04:19.100
because we have significant
amounts of both acetic acid

00:04:19.100 --> 00:04:23.250
and its conjugate base, the
acetate anion, in solution.

00:04:23.250 --> 00:04:24.320
Remember that our goal

00:04:24.320 --> 00:04:27.430
was to calculate the pH
of this buffer solution.

00:04:27.430 --> 00:04:29.940
So first, we need to
calculate the concentration

00:04:29.940 --> 00:04:32.870
of acetic acid and of the acetate anion.

00:04:32.870 --> 00:04:35.090
To find the concentration of acetic acid,

00:04:35.090 --> 00:04:39.260
we take the moles of acetic
acid which is equal to 0.050,

00:04:39.260 --> 00:04:42.440
and we divide by the
total volume of solution.

00:04:42.440 --> 00:04:43.490
We already calculated

00:04:43.490 --> 00:04:45.220
when we mix the two solutions together,

00:04:45.220 --> 00:04:47.810
the total volume was 150 milliliters

00:04:47.810 --> 00:04:50.830
which is equal to 0.150 liters.

00:04:50.830 --> 00:04:54.980
So 0.050 moles divided by 0.150 liters

00:04:54.980 --> 00:04:59.423
gives the concentration of
acetic acid a 0.33 molar.

00:05:00.360 --> 00:05:04.200
For the acetate anion,
we also have 0.050 moles,

00:05:04.200 --> 00:05:08.300
and the total volume of
solution is also 0.150 liters.

00:05:08.300 --> 00:05:10.630
Therefore, the concentration
of the acetate anion

00:05:10.630 --> 00:05:13.570
is also 0.33 molar.

00:05:13.570 --> 00:05:15.440
To find the pH of the buffer solution,

00:05:15.440 --> 00:05:18.350
we can use the
Henderson-Hasselbalch equation.

00:05:18.350 --> 00:05:19.780
The Henderson-Hasselbalch equation

00:05:19.780 --> 00:05:21.480
says the pH of the buffer solution

00:05:21.480 --> 00:05:24.310
is equal to the pKa of the weak acid

00:05:24.310 --> 00:05:27.250
plus the log of the ratio
of the concentration

00:05:27.250 --> 00:05:30.110
of the conjugate base
divided by the concentration

00:05:30.110 --> 00:05:31.430
of the weak acid.

00:05:31.430 --> 00:05:34.970
The weak acid present in our
buffer solution is acetic acid.

00:05:34.970 --> 00:05:37.090
And at 25 degrees Celsius,

00:05:37.090 --> 00:05:41.960
the pKa value of acetic
acid is equal to 4.74.

00:05:41.960 --> 00:05:44.740
The acetate anion is our conjugated base

00:05:44.740 --> 00:05:47.070
and it has a concentration of 0.33 molar,

00:05:47.070 --> 00:05:50.060
so we can plug that into the
Henderson-Hasselbalch equation,

00:05:50.060 --> 00:05:51.980
and the concentration of our weak acid

00:05:51.980 --> 00:05:54.950
is also 0.33 molar.

00:05:54.950 --> 00:05:59.950
Molars cancel and 0.33 divided
by 0.33 is equal to one.

00:06:00.460 --> 00:06:04.710
And the log of one is equal to zero.

00:06:04.710 --> 00:06:06.900
Therefore, for this buffer solution,

00:06:06.900 --> 00:06:11.900
the pH is just equal to 4.74.

00:06:13.060 --> 00:06:15.760
And notice that even though I
calculated the concentration

00:06:15.760 --> 00:06:18.960
of the weak acid and
of the conjugate base,

00:06:18.960 --> 00:06:19.990
I didn't really have to,

00:06:19.990 --> 00:06:22.440
if you look at the
Henderson-Hasselbalch equation.

00:06:22.440 --> 00:06:25.800
Because we have concentration
divided by concentration,

00:06:25.800 --> 00:06:29.300
and concentration, molarity,
is moles per liter.

00:06:29.300 --> 00:06:32.390
And so it's moles divided
by liters, divided by moles,

00:06:32.390 --> 00:06:33.620
divided by liters.

00:06:33.620 --> 00:06:36.480
And since both the weak
acid and the conjugate base

00:06:36.480 --> 00:06:39.240
have the same total volume of solution,

00:06:39.240 --> 00:06:41.590
the total volume of solution would cancel.

00:06:41.590 --> 00:06:42.740
And so, if we want to,

00:06:42.740 --> 00:06:44.540
we could just do a ratio of the moles

00:06:44.540 --> 00:06:46.360
and we would have gotten the same answer,

00:06:46.360 --> 00:06:49.950
a final pH of 4.74.

00:06:49.950 --> 00:06:53.270
Let's look at another method
for making a buffer solution.

00:06:53.270 --> 00:06:55.410
In this case, we're gonna
mix an aqueous solution

00:06:55.410 --> 00:06:57.830
of a weak base with an aqueous solution

00:06:57.830 --> 00:07:01.570
that contains the conjugate
acid to the weak base.

00:07:01.570 --> 00:07:05.540
In this example, our weak
base is ammonia, NH3.

00:07:05.540 --> 00:07:10.490
The conjugate acid to ammonia
is the ammonium ion, NH4+.

00:07:10.490 --> 00:07:13.710
And if we have an aqueous
solution of ammonium chloride,

00:07:13.710 --> 00:07:17.500
in solution, there are
ammonium ions, NH4+.

00:07:19.190 --> 00:07:21.900
So we have a weak base, NH3,

00:07:21.900 --> 00:07:25.100
and its conjugate acid, NH4+.

00:07:25.100 --> 00:07:27.530
And when the two aqueous
solutions are mixed,

00:07:27.530 --> 00:07:31.060
we'll have a significant
amount of both our weak base

00:07:31.060 --> 00:07:33.050
and its conjugate acid.

00:07:33.050 --> 00:07:36.060
Therefore, we will have a buffer solution.

00:07:36.060 --> 00:07:39.510
I often say that a buffer
solution consists of a weak acid

00:07:39.510 --> 00:07:41.200
and its conjugate base.

00:07:41.200 --> 00:07:42.200
In this case,

00:07:42.200 --> 00:07:44.810
I've said the buffer solution
consists of a weak base

00:07:44.810 --> 00:07:46.540
and its conjugate acid.

00:07:46.540 --> 00:07:49.810
So a more general definition
for a buffer solution

00:07:49.810 --> 00:07:53.460
could be a weak conjugate acid-base pair.

00:07:53.460 --> 00:07:56.630
We can calculate the pH of
the buffer solution that forms

00:07:56.630 --> 00:07:58.310
when we mix the two solutions together

00:07:58.310 --> 00:08:01.540
using the Henderson-Hasselbalch equation.

00:08:01.540 --> 00:08:02.373
In this case,

00:08:02.373 --> 00:08:06.670
our numerator is our weak
base which is ammonia

00:08:06.670 --> 00:08:10.100
and our denominator is the
conjugate acid to ammonia

00:08:10.100 --> 00:08:12.650
which is the ammonium ion, NH4+.

00:08:13.570 --> 00:08:17.610
The ammonia solution had a
concentration of 0.16 molar,

00:08:17.610 --> 00:08:20.430
and when we mix 100 milliliters
of the ammonia solution

00:08:20.430 --> 00:08:23.760
with 100 milliliters of the
solution of ammonium chloride,

00:08:23.760 --> 00:08:25.390
the total volume would double.

00:08:25.390 --> 00:08:28.400
So we went from 100
milliliters to 200 milliliters.

00:08:28.400 --> 00:08:30.350
Therefore, since we're
doubling the volume,

00:08:30.350 --> 00:08:33.460
we're halving the
concentration of ammonia.

00:08:33.460 --> 00:08:36.850
So we can put in 0.080 molar

00:08:36.850 --> 00:08:39.620
for the concentration of ammonia.

00:08:39.620 --> 00:08:42.290
Ammonium chloride is a soluble salt.

00:08:42.290 --> 00:08:45.040
Therefore, if we have 0.20 molar

00:08:45.040 --> 00:08:47.930
for the initial concentration
of ammonium chloride,

00:08:47.930 --> 00:08:51.100
we have 0.20 more for
the initial concentration

00:08:51.100 --> 00:08:52.360
of ammonium ions.

00:08:52.360 --> 00:08:54.560
And since we're doubling the volume

00:08:54.560 --> 00:08:56.930
when we mix the two solutions together,

00:08:56.930 --> 00:08:59.350
we are halving the concentration.

00:08:59.350 --> 00:09:00.370
So the concentration

00:09:00.370 --> 00:09:04.810
of ammonium ions in
solution is 0.10 molar.

00:09:04.810 --> 00:09:05.770
So we could plug that

00:09:05.770 --> 00:09:08.750
into the Henderson-Hasselbalch equation.

00:09:08.750 --> 00:09:11.200
So here we have the
concentrations plugged in,

00:09:11.200 --> 00:09:14.320
0.080 molar is the
concentration of ammonia

00:09:14.320 --> 00:09:18.980
and 0.10 molar was the
concentration of the ammonium ion.

00:09:18.980 --> 00:09:20.680
In the Henderson-Hasselbalch equation,

00:09:20.680 --> 00:09:24.120
the pKa is the pKa value of the weak acid,

00:09:24.120 --> 00:09:27.150
which is the ammonium ion, NH4+.

00:09:27.150 --> 00:09:29.060
At 25 degrees Celsius,

00:09:29.060 --> 00:09:33.560
the pKa value of the ammonium
cation is equal to 9.25.

00:09:33.560 --> 00:09:38.096
Molar cancels and when we solve
for the pH of the solution,

00:09:38.096 --> 00:09:42.200
the pH is equal to 9.15.

00:09:42.200 --> 00:09:44.420
So this problem started with a weak base

00:09:44.420 --> 00:09:47.000
and a salt that contained
the conjugate acid

00:09:47.000 --> 00:09:48.560
to that weak base.

00:09:48.560 --> 00:09:50.850
It's also possible to
make a buffer solution

00:09:50.850 --> 00:09:53.960
starting with an aqueous
solution of a weak acid

00:09:53.960 --> 00:09:57.100
and adding a salt that
contains the conjugate base

00:09:57.100 --> 00:09:58.860
to that weak acid.

00:09:58.860 --> 00:10:00.990
For example, to make another buffer,

00:10:00.990 --> 00:10:01.823
we could have started

00:10:01.823 --> 00:10:04.320
with a solution of a
weak acid, acetic acid,

00:10:04.320 --> 00:10:05.490
and to that solution,

00:10:05.490 --> 00:10:08.830
we could have added something
like sodium acetate.

00:10:08.830 --> 00:10:10.797
Sodium acetate is a soluble salt

00:10:10.797 --> 00:10:14.070
that dissociates completely in solution

00:10:14.070 --> 00:10:17.270
to produce sodium cations
and acetate anions.

00:10:17.270 --> 00:10:20.220
And since we would have
a significant amount

00:10:20.220 --> 00:10:23.180
of both a weak acid
and its conjugate base,

00:10:23.180 --> 00:10:25.083
we would have a buffer solution.


Henderson–Hasselbalch equation

WEBVTT
Kind: captions
Language: en

00:00:00.480 --> 00:00:02.400
- [Instructor] The
Henderson-Hasselbalch equation

00:00:02.400 --> 00:00:03.970
is an equation that's often used

00:00:03.970 --> 00:00:07.410
to calculate the pH of buffer solutions.

00:00:07.410 --> 00:00:10.470
Buffers consists of a weak
acid and its conjugate base.

00:00:10.470 --> 00:00:12.330
So for a generic weak acid,

00:00:12.330 --> 00:00:13.980
we could call that HA,

00:00:13.980 --> 00:00:16.507
and therefore, its
conjugate base would be A-.

00:00:17.370 --> 00:00:20.130
To calculate the pH of
the buffer solution,

00:00:20.130 --> 00:00:23.300
we would find the pKa of the weak acid,

00:00:23.300 --> 00:00:26.730
and to that we would add
the log of the concentration

00:00:26.730 --> 00:00:29.700
of the conjugate base
divided by the concentration

00:00:29.700 --> 00:00:31.510
of the weak acid.

00:00:31.510 --> 00:00:33.480
Let's use the
Henderson-Hasselbalch equation

00:00:33.480 --> 00:00:36.950
to calculate the pH of an
aqueous buffer solution

00:00:36.950 --> 00:00:40.290
that consists of acetic
acid and its conjugate base,

00:00:40.290 --> 00:00:42.040
the acetate anion.

00:00:42.040 --> 00:00:43.960
And let's use this particulate diagram

00:00:43.960 --> 00:00:47.520
to help us calculate the
pH of the buffer solution.

00:00:47.520 --> 00:00:49.920
Remember that the goal
of a particulate diagram

00:00:49.920 --> 00:00:52.480
is not to represent every
particle in the solution,

00:00:52.480 --> 00:00:54.500
but to give us an idea
about what's going on

00:00:54.500 --> 00:00:56.250
in the entire solution.

00:00:56.250 --> 00:00:58.640
And also, when looking at
the particulate diagrams

00:00:58.640 --> 00:01:00.060
of buffer solutions,

00:01:00.060 --> 00:01:04.160
water molecules and cations
are often left out for clarity.

00:01:04.160 --> 00:01:06.710
Let's count the number of
particles of acetic acid

00:01:06.710 --> 00:01:08.710
in our particulate diagram.

00:01:08.710 --> 00:01:12.730
So in our diagram, there are
five particles of acetic acid,

00:01:12.730 --> 00:01:17.730
and for the acetate anion,
there are also five.

00:01:18.120 --> 00:01:19.700
Because there are five particles

00:01:19.700 --> 00:01:22.250
of both acetic acid and the acetate anion,

00:01:22.250 --> 00:01:25.030
the concentration of acetic acid

00:01:25.030 --> 00:01:29.483
is equal to the concentration
of the acetate anion.

00:01:30.440 --> 00:01:32.980
Next, let's think about the
Henderson-Hasselbalch equation.

00:01:32.980 --> 00:01:35.810
Our goal is to calculate the
pH of this buffer solution

00:01:35.810 --> 00:01:38.030
represented in the particulate diagram.

00:01:38.030 --> 00:01:41.990
And so first, we need to know
the pKa of the weak acid,

00:01:41.990 --> 00:01:44.460
which is acetic acid.

00:01:44.460 --> 00:01:48.110
At 25 degrees Celsius, the
Ka value for acetic acid

00:01:48.110 --> 00:01:51.150
is equal to 1.8 times 10
to the negative fifth.

00:01:51.150 --> 00:01:53.870
The Ka value is less than
one because acetic acid

00:01:53.870 --> 00:01:55.490
is a weak acid.

00:01:55.490 --> 00:01:57.890
To find the pKa of acetic acid,

00:01:57.890 --> 00:02:01.040
we take the negative log of the Ka value.

00:02:01.040 --> 00:02:04.350
So the negative log of 1.8
times 10 to the negative fifth

00:02:04.350 --> 00:02:07.960
is equal to 4.74.

00:02:07.960 --> 00:02:10.500
So we can go back to the
Henderson-Hasselbalch equation

00:02:10.500 --> 00:02:14.820
and write that the pH is equal to the pKa,

00:02:14.820 --> 00:02:18.750
which we just calculated to be 4.74

00:02:18.750 --> 00:02:23.610
plus the log of the concentration
of the conjugate base.

00:02:23.610 --> 00:02:26.320
And the conjugate base
is the acetate anions,

00:02:26.320 --> 00:02:29.187
so let's write that in here, CH3COO-,

00:02:31.960 --> 00:02:35.430
and that's divided by the
concentration of the weak acid,

00:02:35.430 --> 00:02:39.723
which is acetic acid, CH3COOH.

00:02:40.820 --> 00:02:41.720
We've already figured out

00:02:41.720 --> 00:02:43.770
that the concentration of acetic acid

00:02:43.770 --> 00:02:47.790
is equal to the concentration
of the acetate anion.

00:02:47.790 --> 00:02:50.300
Therefore, the concentration
of the acetate anion

00:02:50.300 --> 00:02:53.060
divided by the
concentration of acetic acid

00:02:53.060 --> 00:02:55.100
is just equal to one.

00:02:55.100 --> 00:02:59.480
And the log of one is equal to zero.

00:02:59.480 --> 00:03:01.070
So let's go ahead and write that in here,

00:03:01.070 --> 00:03:04.140
the log of one is equal to zero.

00:03:04.140 --> 00:03:07.050
Therefore, the pH of the buffer solution

00:03:07.050 --> 00:03:12.050
is equal to 4.74 plus zero

00:03:12.080 --> 00:03:14.760
or just 4.74.

00:03:14.760 --> 00:03:17.070
So whenever the concentration
of the weak acid

00:03:17.070 --> 00:03:20.320
is equal to the concentration
of the conjugate base,

00:03:20.320 --> 00:03:22.000
the pH of the buffer solution

00:03:22.000 --> 00:03:25.890
is equal to the pKa of the weak acid.

00:03:25.890 --> 00:03:28.640
Let's look at another particulate diagram.

00:03:28.640 --> 00:03:32.640
We still have an acetic
acid-acetate buffer solution.

00:03:32.640 --> 00:03:34.770
However, this is a
different buffer solution

00:03:34.770 --> 00:03:36.750
than the previous problem.

00:03:36.750 --> 00:03:38.360
So let's count our particles.

00:03:38.360 --> 00:03:42.400
For acetic acid, there are six particles

00:03:42.400 --> 00:03:46.990
and for the acetate anion,
there are only four.

00:03:46.990 --> 00:03:50.410
Since we have more acetic acid particles

00:03:50.410 --> 00:03:51.720
than acetate particles,

00:03:51.720 --> 00:03:54.080
the concentration of acetic acid

00:03:54.080 --> 00:03:59.080
is greater than the concentration
of the acetate anion.

00:03:59.210 --> 00:04:01.310
We can use the
Henderson-Hasselbalch equation

00:04:01.310 --> 00:04:04.130
to think about the pH
of this buffer solution.

00:04:04.130 --> 00:04:07.010
So the pH is equal to the pKa,

00:04:07.010 --> 00:04:09.410
which we calculated in
the previous problem

00:04:09.410 --> 00:04:10.940
for acetic acid,

00:04:10.940 --> 00:04:14.120
it's 4.74 at 25 degrees Celsius,

00:04:14.120 --> 00:04:17.700
plus the log of the concentration
of the acetate anion,

00:04:17.700 --> 00:04:21.520
divided by the concentration
of acetic acid.

00:04:21.520 --> 00:04:23.750
In this case, the
concentration of acetic acid

00:04:23.750 --> 00:04:27.750
is greater than the concentration
of the acetate anion.

00:04:27.750 --> 00:04:31.280
Therefore, we have a smaller concentration

00:04:31.280 --> 00:04:34.090
divided by a larger concentration.

00:04:34.090 --> 00:04:36.270
So we have a number less than one.

00:04:36.270 --> 00:04:41.230
And the log of a number
less than one is negative.

00:04:41.230 --> 00:04:46.230
Therefore, all of this would
be negative or less than zero.

00:04:46.710 --> 00:04:51.540
So we would be subtracting
a number from 4.74.

00:04:51.540 --> 00:04:55.010
Therefore, we can say
the pH of the solution

00:04:55.010 --> 00:05:00.010
would be less than 4.74.

00:05:00.080 --> 00:05:02.160
Let's do one more particulate diagram

00:05:02.160 --> 00:05:05.460
of an acetic acid-acetate buffer solution.

00:05:05.460 --> 00:05:07.300
Once again, we count our particles.

00:05:07.300 --> 00:05:11.710
So for acetic acid, this
time, there are four particles

00:05:11.710 --> 00:05:14.160
and for the acetate anion,

00:05:14.160 --> 00:05:17.320
this time, there are six particles.

00:05:17.320 --> 00:05:21.340
Since we have only four
particles of acetic acid

00:05:21.340 --> 00:05:24.170
and six particles of the acetate anion,

00:05:24.170 --> 00:05:25.930
the concentration of acetic acid

00:05:25.930 --> 00:05:29.970
is less than the concentration
of the acetate anion

00:05:29.970 --> 00:05:32.660
or we could say the concentration
of the acetate anion

00:05:32.660 --> 00:05:36.220
is greater than the
concentration of acetic acid.

00:05:36.220 --> 00:05:38.420
Thinking about the
Henderson-Hasselbalch equation,

00:05:38.420 --> 00:05:42.320
once again, the pKa is equal to 4.74,

00:05:42.320 --> 00:05:44.050
and we need to think about the ratio

00:05:44.050 --> 00:05:46.910
of the concentration of the acetate anion

00:05:46.910 --> 00:05:49.760
to the concentration of acetic acid.

00:05:49.760 --> 00:05:52.570
For this example, the
concentration of the acetate anion

00:05:52.570 --> 00:05:56.110
is greater than the
concentration of acetic acid.

00:05:56.110 --> 00:05:59.680
Therefore, the ratio
would be greater than one,

00:05:59.680 --> 00:06:03.050
and the log of a number greater than one

00:06:03.050 --> 00:06:06.330
is positive or greater than zero.

00:06:06.330 --> 00:06:11.330
Therefore, we would be
adding a number to 4.74.

00:06:11.370 --> 00:06:13.250
So for this buffer solution,

00:06:13.250 --> 00:06:17.993
the pH would be greater than 4.74.

00:06:19.360 --> 00:06:21.320
Finally, let's summarize
what we've learned

00:06:21.320 --> 00:06:24.370
from our three different
particulate diagrams.

00:06:24.370 --> 00:06:25.560
In the first example,

00:06:25.560 --> 00:06:27.360
the concentration of the weak acid

00:06:27.360 --> 00:06:30.560
was equal to the concentration
of the conjugate base.

00:06:30.560 --> 00:06:33.410
And therefore, the pH
of the buffer solution

00:06:33.410 --> 00:06:37.110
was equal to the pKa of the weak acid.

00:06:37.110 --> 00:06:38.310
In the second example,

00:06:38.310 --> 00:06:40.040
the concentration of the weak acid

00:06:40.040 --> 00:06:43.420
was greater than the concentration
of the conjugate base.

00:06:43.420 --> 00:06:46.330
And therefore, the pH
of the buffer solution

00:06:46.330 --> 00:06:49.243
is less than the pKa of the weak acid.

00:06:50.330 --> 00:06:51.890
And in the third example,

00:06:51.890 --> 00:06:54.370
the concentration of the weak acid

00:06:54.370 --> 00:06:58.090
was less than the concentration
of the conjugate base.

00:06:58.090 --> 00:07:00.490
Therefore, the pH of the buffer solution

00:07:00.490 --> 00:07:04.080
was greater than the pKa of the weak acid.

00:07:04.080 --> 00:07:06.980
So if we know the pH of a buffer solution,

00:07:06.980 --> 00:07:10.030
we can think about the
Henderson-Hasselbalch equation

00:07:10.030 --> 00:07:12.640
to think about the relative concentrations

00:07:12.640 --> 00:07:15.690
of the weak acid and the conjugate base.

00:07:15.690 --> 00:07:18.550
For example, if we have a
particular buffer solution

00:07:18.550 --> 00:07:20.740
and we know the pH of the buffer solution

00:07:20.740 --> 00:07:23.360
is less than the pKa of the weak acid,

00:07:23.360 --> 00:07:26.110
we know that in that buffer
at that moment in time,

00:07:26.110 --> 00:07:28.190
the concentration of the weak acid

00:07:28.190 --> 00:07:32.523
is greater than the concentration
of the conjugate base.


Properties of buffers

WEBVTT
Kind: captions
Language: en

00:00:00.300 --> 00:00:01.830
- [Instructor] A buffer solution consists

00:00:01.830 --> 00:00:04.160
of a significant amount of a weak acid

00:00:04.160 --> 00:00:06.280
and its conjugate base.

00:00:06.280 --> 00:00:09.500
Let's say we have a generic weak acid, HA,

00:00:09.500 --> 00:00:11.820
and its conjugate base, A-.

00:00:11.820 --> 00:00:14.450
And we're gonna use some
particulate diagrams

00:00:14.450 --> 00:00:17.000
to try to understand how buffers work.

00:00:17.000 --> 00:00:19.060
So for our first particulate diagram,

00:00:19.060 --> 00:00:21.900
let's count out how many
particles we have of each.

00:00:21.900 --> 00:00:24.390
So first let's count how many HAs we have.

00:00:24.390 --> 00:00:27.953
So there's 1, 2, 3, 4, 5 HAs,

00:00:29.200 --> 00:00:34.200
and there's also, for A-,
there's 1, 2, 3, 4, 5 A minuses.

00:00:36.170 --> 00:00:38.890
And when looking at a
particulate diagram of a buffer,

00:00:38.890 --> 00:00:42.190
usually water molecules
are omitted for clarity.

00:00:42.190 --> 00:00:44.850
And also keep in mind that
this particulate diagram

00:00:44.850 --> 00:00:48.750
is just meant to represent a
small portion of the solution,

00:00:48.750 --> 00:00:50.470
so we can get an idea
about what's happening

00:00:50.470 --> 00:00:52.320
in the entire solution.

00:00:52.320 --> 00:00:54.313
Also notice that like water molecules,

00:00:54.313 --> 00:00:58.490
cations are also left out
of the particulate diagram.

00:00:58.490 --> 00:01:02.050
So we have five HA particles
and five A- particles

00:01:02.050 --> 00:01:03.840
in our aqueous solution.

00:01:03.840 --> 00:01:07.420
Having equal amounts of a weak
acid and its conjugate base

00:01:07.420 --> 00:01:09.720
is a good buffer solution.

00:01:09.720 --> 00:01:11.560
Let's see what happens
to the buffer solution

00:01:11.560 --> 00:01:14.330
if we add in a small amount of acid.

00:01:14.330 --> 00:01:17.240
So here I'm drawing in an H+ ion,

00:01:17.240 --> 00:01:19.850
and let's think about adding this H+ ion

00:01:19.850 --> 00:01:22.000
to our buffer solution.

00:01:22.000 --> 00:01:25.120
When the H+ ion is added to the solution,

00:01:25.120 --> 00:01:28.660
the base that is present
will react with the H+ ion

00:01:28.660 --> 00:01:29.960
to neutralize it.

00:01:29.960 --> 00:01:33.373
So the added H+ reacts with A- to form HA.

00:01:34.260 --> 00:01:36.030
So for the particulate diagrams,

00:01:36.030 --> 00:01:38.440
this added H+ is going to react

00:01:38.440 --> 00:01:42.140
with one of the A minuses
present in the buffer solution.

00:01:42.140 --> 00:01:46.070
So the H+ and the A- form an HA.

00:01:46.070 --> 00:01:50.210
So we're gonna go from
five HAs to six HAs.

00:01:50.210 --> 00:01:53.140
So let's look at this next
particulate diagram here.

00:01:53.140 --> 00:01:57.220
We can see there are now
six HAs in the solution,

00:01:57.220 --> 00:01:59.550
so let me write down six here.

00:01:59.550 --> 00:02:03.580
And since we started with five,
A minuses and we lost one,

00:02:03.580 --> 00:02:07.780
we should have only four
A minuses in solution now.

00:02:07.780 --> 00:02:09.340
So let's write down a four here.

00:02:09.340 --> 00:02:12.790
So you started off with
five HAs and five A minuses,

00:02:12.790 --> 00:02:15.180
and upon the addition of
a small amount of acid,

00:02:15.180 --> 00:02:18.180
the acid was neutralized by
the base that was present,

00:02:18.180 --> 00:02:22.210
and we formed six HAs and four A minuses.

00:02:22.210 --> 00:02:25.440
So a buffer solution
resists changes in pH.

00:02:25.440 --> 00:02:27.840
So the added H+ was neutralized

00:02:27.840 --> 00:02:29.770
by the presence of the base.

00:02:29.770 --> 00:02:31.920
If the buffer solution
had not been present,

00:02:31.920 --> 00:02:33.600
if we just had some water

00:02:33.600 --> 00:02:35.290
and we added some H+,

00:02:35.290 --> 00:02:37.990
the pH would have changed dramatically.

00:02:37.990 --> 00:02:41.080
One way to write the acid-base
neutralization reaction

00:02:41.080 --> 00:02:45.960
that occurred is to write
H+ plus A- goes to HA.

00:02:45.960 --> 00:02:48.690
However, since H3O+ and H+

00:02:48.690 --> 00:02:51.350
are used interchangeably in chemistry,

00:02:51.350 --> 00:02:54.170
we could have also written
the net ionic equation

00:02:54.170 --> 00:02:59.170
as H3O+ plus A- goes to HA and H2O.

00:02:59.570 --> 00:03:02.700
Next, let's go back to our
middle particulate diagram

00:03:02.700 --> 00:03:05.880
with five HA and five A-.

00:03:05.880 --> 00:03:09.430
And this time let's try
to add some hydroxide ions

00:03:09.430 --> 00:03:10.610
to the solution.

00:03:10.610 --> 00:03:12.040
So think about,

00:03:12.040 --> 00:03:13.320
let me go ahead and draw an arrow here,

00:03:13.320 --> 00:03:15.490
so we're gonna add a small amount of base

00:03:15.490 --> 00:03:18.120
to our buffer solution.

00:03:18.120 --> 00:03:21.010
The hydroxide anion will
react with the weak acid

00:03:21.010 --> 00:03:25.550
that is present, HA, to form H2O and A-.

00:03:25.550 --> 00:03:27.270
So for the particulate diagrams,

00:03:27.270 --> 00:03:30.973
we can think about this OH-
reacting with one of the HAs

00:03:31.960 --> 00:03:34.290
to form H2O and an A-.

00:03:35.760 --> 00:03:38.000
Since we're using up one of the HAs,

00:03:38.000 --> 00:03:43.000
we're gonna go from five
HAs down to four HAs.

00:03:43.150 --> 00:03:45.573
So let me write down here, four HAs.

00:03:46.890 --> 00:03:50.740
And when this HA reacts,
it's gonna turn into an A-.

00:03:50.740 --> 00:03:54.700
So we're gonna go from
five A minuses up to six.

00:03:54.700 --> 00:03:55.730
So let's count them over here.

00:03:55.730 --> 00:03:59.560
1, 2, 3, 4, 5, 6.

00:03:59.560 --> 00:04:02.440
So let's write in six A minuses.

00:04:02.440 --> 00:04:03.910
If there is no buffer present

00:04:03.910 --> 00:04:06.940
and we're just adding
hydroxide anions to water,

00:04:06.940 --> 00:04:09.560
the pH would change dramatically.

00:04:09.560 --> 00:04:11.770
However, with a buffer present,

00:04:11.770 --> 00:04:14.980
since there is a weak acid, HA, present

00:04:14.980 --> 00:04:19.040
to neutralize the added hydroxide anions,

00:04:19.040 --> 00:04:23.320
the buffer solution
resists a change to the pH.

00:04:23.320 --> 00:04:26.380
So let's summarize how
buffer solutions work.

00:04:26.380 --> 00:04:29.770
If we add a small amount of an acid, H+,

00:04:29.770 --> 00:04:31.380
to a buffer solution,

00:04:31.380 --> 00:04:34.130
the conjugate base that's present, A-,

00:04:34.130 --> 00:04:36.370
neutralizes the added acid.

00:04:36.370 --> 00:04:40.330
Therefore, the buffer solution
resists a change in pH.

00:04:40.330 --> 00:04:43.660
And if we add a small amount of a base,

00:04:43.660 --> 00:04:45.890
the weak acid that's present

00:04:45.890 --> 00:04:49.610
will neutralize the hydroxide anions.

00:04:49.610 --> 00:04:54.110
Therefore, the buffer solution
resists a change in pH.

00:04:54.110 --> 00:04:57.070
Let's say we have an aqueous
solution of acetic acid

00:04:57.070 --> 00:05:00.940
and an aqueous solution of sodium acetate.

00:05:00.940 --> 00:05:03.880
And let's say we have
equal moles of acetic acid

00:05:03.880 --> 00:05:06.170
and of sodium acetate.

00:05:06.170 --> 00:05:07.760
Mixing these two solutions together

00:05:07.760 --> 00:05:10.180
would form a buffer solution.

00:05:10.180 --> 00:05:12.980
To understand why this
forms a buffer solution,

00:05:12.980 --> 00:05:15.160
let's first think about acetic acid.

00:05:15.160 --> 00:05:17.130
Acetic acid is a weak acid

00:05:17.130 --> 00:05:21.040
and only partially ionizes
in aqueous solution.

00:05:21.040 --> 00:05:22.670
Therefore, in aqueous solution,

00:05:22.670 --> 00:05:25.953
we have mostly acetic acid, CH3COOH.

00:05:28.120 --> 00:05:30.710
Sodium acetate is a soluble salt

00:05:30.710 --> 00:05:34.090
and it dissociates completely
in aqueous solution.

00:05:34.090 --> 00:05:35.670
Therefore, in aqueous solution,

00:05:35.670 --> 00:05:38.220
we have sodium cations and
acetate anions, CH3COO-.

00:05:43.020 --> 00:05:47.030
The acetate anion is the
conjugate base to acetic acid.

00:05:47.030 --> 00:05:49.330
Therefore, in aqueous solution,

00:05:49.330 --> 00:05:52.410
we have a weak acid
and its conjugate base,

00:05:52.410 --> 00:05:54.950
and so we have a buffer solution.

00:05:54.950 --> 00:05:56.940
If we try adding a small amount of acid

00:05:56.940 --> 00:05:58.660
to the buffer solution,

00:05:58.660 --> 00:06:01.860
the conjugate base
that's present will react

00:06:01.860 --> 00:06:04.170
with the acid and neutralize it.

00:06:04.170 --> 00:06:06.930
So in the balanced net ionic equation,

00:06:06.930 --> 00:06:10.030
the added acid hydronium ion, H3O+,

00:06:10.030 --> 00:06:15.030
reacts with the acetate anion
to form acetic acid and water.

00:06:15.030 --> 00:06:18.300
So the added hydronium
ion was neutralized,

00:06:18.300 --> 00:06:22.330
and the buffer has resisted
a dramatic change in pH.

00:06:22.330 --> 00:06:24.380
If we try adding a small amount of base

00:06:24.380 --> 00:06:26.090
to the buffer solution,

00:06:26.090 --> 00:06:28.090
the weak acid that is present

00:06:28.090 --> 00:06:30.690
will neutralize the added base.

00:06:30.690 --> 00:06:33.340
So in the balanced net ionic equation,

00:06:33.340 --> 00:06:36.090
hydroxide anions react with acetic acid

00:06:36.090 --> 00:06:39.330
to form the acetate anion and water.

00:06:39.330 --> 00:06:42.670
So the added base was neutralized.

00:06:42.670 --> 00:06:43.820
So to summarize,

00:06:43.820 --> 00:06:46.380
the acetic acid-acetate buffer system

00:06:46.380 --> 00:06:48.600
resists dramatic changes in pH

00:06:48.600 --> 00:06:51.680
when small amounts of
acid or base are added.

00:06:51.680 --> 00:06:52.550
And I just noticed,

00:06:52.550 --> 00:06:55.650
I forgot to include the
L for liquid for water

00:06:55.650 --> 00:06:58.153
in the balanced net ionic equations.


Cellular respiration

WEBVTT
Kind: captions
Language: en

00:00:00.320 --> 00:00:01.153
- [Instructor] In this video,

00:00:01.153 --> 00:00:03.170
we're going to talk about
cellular respiration,

00:00:03.170 --> 00:00:04.865
which sounds like a very fancy thing,

00:00:04.865 --> 00:00:08.466
but it's really just about
the biochemical processes

00:00:08.466 --> 00:00:10.520
that can take things

00:00:10.520 --> 00:00:13.170
that we find in food and convert

00:00:13.170 --> 00:00:15.254
it into forms of energy that we can use

00:00:15.254 --> 00:00:19.130
to do things like run and
maintain our body temperature,

00:00:19.130 --> 00:00:21.321
and maintain body homeostasis.

00:00:21.321 --> 00:00:25.780
So to get into the chemistry
of cellular respiration,

00:00:25.780 --> 00:00:28.490
and this really is an overview video,

00:00:28.490 --> 00:00:32.460
we will start with the chemical
equation for respiration.

00:00:32.460 --> 00:00:34.686
And what it's all about is a series

00:00:34.686 --> 00:00:37.650
of steps that when you
look at them in aggregate,

00:00:37.650 --> 00:00:40.138
you're starting with the
glucose right over here,

00:00:40.138 --> 00:00:42.086
using oxygen, and that's why we have

00:00:42.086 --> 00:00:44.090
to breathe really hard in order

00:00:44.090 --> 00:00:46.080
to do our cellular respiration.

00:00:46.080 --> 00:00:48.450
And it's going to yield
some carbon dioxide,

00:00:48.450 --> 00:00:51.120
which we also need to
breathe hard to exhale,

00:00:51.120 --> 00:00:53.700
some water, and some energy.

00:00:53.700 --> 00:00:55.600
Now that energy he is in the form of heat,

00:00:55.600 --> 00:00:57.580
which can help us maintain
our body temperature,

00:00:57.580 --> 00:00:59.360
especially if it's cold outside side.

00:00:59.360 --> 00:01:01.322
But also ATP.

00:01:01.322 --> 00:01:05.449
Now you might be wondering, what is ATP?

00:01:05.449 --> 00:01:07.930
And to help us answer that question,

00:01:07.930 --> 00:01:10.110
I will show you a picture of ATP,

00:01:10.110 --> 00:01:11.691
and I will also show you a picture

00:01:11.691 --> 00:01:14.500
of glucose or a visualization of it.

00:01:14.500 --> 00:01:17.032
Now you don't have to memorize
what these structures are,

00:01:17.032 --> 00:01:20.793
but what's really going
on here is that glucose,

00:01:20.793 --> 00:01:23.970
as you are able to shape
it into other things,

00:01:23.970 --> 00:01:26.030
as you're able to break
the bonds in glucose,

00:01:26.030 --> 00:01:29.130
and having its constituents
form bonds with other things,

00:01:29.130 --> 00:01:31.200
that has a net release of energy.

00:01:31.200 --> 00:01:32.641
And that energy can be used

00:01:32.641 --> 00:01:34.190
to take what's known

00:01:34.190 --> 00:01:37.490
as ADP that has two phosphate groups,

00:01:37.490 --> 00:01:41.120
and add a third phosphate
group onto it right over here.

00:01:41.120 --> 00:01:43.010
Now you see it might
say, why is that useful?

00:01:43.010 --> 00:01:45.883
Why is that a more readily
usable form of energy?

00:01:45.883 --> 00:01:48.441
Well, as you go forward
in your biological journey

00:01:48.441 --> 00:01:50.410
or your understanding of biology,

00:01:50.410 --> 00:01:52.896
you'll see that ATP molecules like this,

00:01:52.896 --> 00:01:54.650
by losing that phosphate

00:01:54.650 --> 00:01:57.100
and allowing that phosphate
to bond to other things

00:01:57.100 --> 00:01:58.359
can actually release energy

00:01:58.359 --> 00:01:59.990
and can fuel muscles,

00:01:59.990 --> 00:02:02.352
can fuel other biological processes.

00:02:02.352 --> 00:02:04.180
Now to understand the steps of it,

00:02:04.180 --> 00:02:06.563
we will start in the cytosol of a cell,

00:02:06.563 --> 00:02:11.180
where a process known as
glycolysis takes place.

00:02:11.180 --> 00:02:15.410
And glycolysis literally
means the breaking of glucose.

00:02:15.410 --> 00:02:18.022
So let me write it down, glycolysis.

00:02:18.022 --> 00:02:21.690
And what it does is it
breaks each glucose molecule

00:02:21.690 --> 00:02:25.590
into two molecules known as pyruvate.

00:02:25.590 --> 00:02:27.340
Now just that process alone,

00:02:27.340 --> 00:02:29.146
and we'll go into much
more depth in other videos,

00:02:29.146 --> 00:02:31.686
does start to produce some ATPs,

00:02:31.686 --> 00:02:36.686
and also helps produce some
molecules known as NADH.

00:02:36.950 --> 00:02:38.920
And I know this is all
sounding very complex.

00:02:38.920 --> 00:02:42.784
But you will have a
molecule known as NAD+,

00:02:42.784 --> 00:02:44.890
if you want to know what it looks like,

00:02:44.890 --> 00:02:46.180
it looks like this.

00:02:46.180 --> 00:02:49.010
Once again, don't get too
bogged down in the details.

00:02:49.010 --> 00:02:50.120
It is worth noting,

00:02:50.120 --> 00:02:53.580
NAD stands for nicotinamide
adenine dinucleotide.

00:02:53.580 --> 00:02:54.880
And we also noticed that ATP stands

00:02:54.880 --> 00:02:57.670
for adenosine triphosphate.

00:02:57.670 --> 00:03:00.880
And so you have these
very molecular components

00:03:00.880 --> 00:03:02.930
that are showing up in
different places in biology,

00:03:02.930 --> 00:03:05.750
and you might also
recognize that adenosine

00:03:05.750 --> 00:03:08.550
is involved in the
formation of DNA as well.

00:03:08.550 --> 00:03:09.383
So once again,

00:03:09.383 --> 00:03:12.830
these molecules are adapted
and reused all over the place.

00:03:12.830 --> 00:03:14.641
But going back to our journey

00:03:14.641 --> 00:03:18.148
of cellular respiration, an NAD+ molecule,

00:03:18.148 --> 00:03:21.340
if you were to add to
that two hydrogen protons,

00:03:21.340 --> 00:03:23.457
and this is the important
part, two electrons,

00:03:23.457 --> 00:03:27.652
it will be reduced to NADH.

00:03:27.652 --> 00:03:30.760
And remember, reduction is
the gaining of electrons,

00:03:30.760 --> 00:03:32.150
which is happening right over here.

00:03:32.150 --> 00:03:34.410
And the reason why these two electrons

00:03:34.410 --> 00:03:35.609
are really interesting is,

00:03:35.609 --> 00:03:38.370
in NADH, they're in a
fairly high energy state.

00:03:38.370 --> 00:03:39.480
And as we'll see,

00:03:39.480 --> 00:03:41.112
as they're able to go to other molecules

00:03:41.112 --> 00:03:43.440
and go to lower and lower energy states,

00:03:43.440 --> 00:03:44.765
they're able to do useful things

00:03:44.765 --> 00:03:48.450
that can eventually end up
in the production of ATP.

00:03:48.450 --> 00:03:50.275
It's essentially a transfer of energy.

00:03:50.275 --> 00:03:53.660
So glycolysis is directly
producing some ATPs,

00:03:53.660 --> 00:03:57.780
and it's also reducing NAD
in this way to produce NADH.

00:03:57.780 --> 00:04:00.857
For the next stage, we have
to go into the mitochondria,

00:04:00.857 --> 00:04:04.710
which is often known as
the powerhouse of the cell,

00:04:04.710 --> 00:04:07.283
where now our pyruvate will enter

00:04:07.283 --> 00:04:11.050
into the mitochondrial
matrix right over here.

00:04:11.050 --> 00:04:15.102
And that's where the
citric acid cycle occurs.

00:04:15.102 --> 00:04:19.326
And the citric acid cycle
is going to use a derivative

00:04:19.326 --> 00:04:22.654
of the pyruvate, which
we got from glycolysis.

00:04:22.654 --> 00:04:24.450
You don't have to know all the details,

00:04:24.450 --> 00:04:25.709
it's called acetylcholine.

00:04:25.709 --> 00:04:28.690
But that's going to go through
a series of transformations.

00:04:28.690 --> 00:04:30.460
And the reason why it's called a cycle,

00:04:30.460 --> 00:04:33.280
there's some molecules that
react with the acetyl-CoA,

00:04:33.280 --> 00:04:35.180
and then through a series
of transformations,

00:04:35.180 --> 00:04:36.710
get back to where they started.

00:04:36.710 --> 00:04:38.740
And the reason why it's
called a citric acid cycle

00:04:38.740 --> 00:04:40.345
is one of those intermediaries is citrate.

00:04:40.345 --> 00:04:45.330
But this process, once again,
produces more ATPs directly,

00:04:45.330 --> 00:04:46.868
but it also produces more NADHs,

00:04:46.868 --> 00:04:49.788
and it also is able to
do something similar

00:04:49.788 --> 00:04:51.260
to another molecule.

00:04:51.260 --> 00:04:53.660
And once again, I'm not going
to go into all of the details.

00:04:53.660 --> 00:04:55.830
But we're able to go
from another molecule,

00:04:55.830 --> 00:04:59.343
known as flavin adenine dinucleotide, FAD,

00:04:59.343 --> 00:05:01.630
plus two hydrogen protons,

00:05:01.630 --> 00:05:04.733
plus two electrons to get to FADH2,

00:05:06.810 --> 00:05:09.102
which once again is an
interesting molecule,

00:05:09.102 --> 00:05:12.470
because it has these electrons
in a higher energy level,

00:05:12.470 --> 00:05:15.130
which, through a series
of molecular processes,

00:05:15.130 --> 00:05:17.716
which you'll go into much
detail in future courses on,

00:05:17.716 --> 00:05:19.860
you are able to do useful work.

00:05:19.860 --> 00:05:21.879
You're able to transfer energy.

00:05:21.879 --> 00:05:24.464
So once you have a few ATPs

00:05:24.464 --> 00:05:27.504
and a bunch of NADHs and FADHs,

00:05:27.504 --> 00:05:30.010
you then go into something known

00:05:30.010 --> 00:05:32.570
as the electron transport chain.

00:05:32.570 --> 00:05:35.000
And this is essentially
where those electrons go

00:05:35.000 --> 00:05:36.060
from a high energy state

00:05:36.060 --> 00:05:38.120
and they get transferred
from one molecule to another,

00:05:38.120 --> 00:05:40.480
actually along this
membrane right over here.

00:05:40.480 --> 00:05:41.491
And as they do, the proteins

00:05:41.491 --> 00:05:43.530
that they are interacting with are able

00:05:43.530 --> 00:05:45.010
to use that energy in order

00:05:45.010 --> 00:05:46.720
to pump hydrogen protons

00:05:46.720 --> 00:05:50.210
into this intermembrane
space of the mitochondria.

00:05:50.210 --> 00:05:53.078
And then that concentration
gradient of hydrogen protons,

00:05:53.078 --> 00:05:56.000
it's released through another enzyme,

00:05:56.000 --> 00:05:59.385
which is actually able to
produce the actual ATP.

00:05:59.385 --> 00:06:01.863
So I know that is a lot to process,

00:06:01.863 --> 00:06:04.440
but this is meant to be just an overview.

00:06:04.440 --> 00:06:06.040
I know you might have a lot of questions

00:06:06.040 --> 00:06:08.120
as I did the first time
that I learned this.

00:06:08.120 --> 00:06:09.499
But the important thing to realize,

00:06:09.499 --> 00:06:11.440
that glucose does store energy,

00:06:11.440 --> 00:06:12.840
but we don't use it directly.

00:06:12.840 --> 00:06:14.540
We have to go through cellular respiration

00:06:14.540 --> 00:06:17.060
to convert that glucose into ATPs,

00:06:17.060 --> 00:06:18.637
which is more readily used by cells.

00:06:18.637 --> 00:06:20.770
Now the various steps are also going

00:06:20.770 --> 00:06:22.570
to produce heat as they release energy,

00:06:22.570 --> 00:06:25.101
which could also be useful for the cell.

00:06:25.101 --> 00:06:28.660
Now, one final point, you
might say glucose, well,

00:06:28.660 --> 00:06:30.050
that's only one form of food.

00:06:30.050 --> 00:06:31.376
You showed a picture of bread initially.

00:06:31.376 --> 00:06:33.559
Well, carbohydrates are made up of chains

00:06:33.559 --> 00:06:35.425
of simple sugars like glucose.

00:06:35.425 --> 00:06:36.940
And if we're thinking about things

00:06:36.940 --> 00:06:39.255
like protein or fats, which
you could also use for energy,

00:06:39.255 --> 00:06:40.921
those are going to be adapted

00:06:40.921 --> 00:06:44.588
and enter at different phases
of cellular respiration.

00:06:44.588 --> 00:06:45.970
But at some point, you're going

00:06:45.970 --> 00:06:47.360
to have a very similar process.

00:06:47.360 --> 00:06:50.728
So I lied, I actually
have one last, last point.

00:06:50.728 --> 00:06:55.384
We talked a lot about glucose
as it enters into glycolysis,

00:06:55.384 --> 00:06:58.300
and then the pyruvate enters
into the mitochondria.

00:06:58.300 --> 00:06:59.379
But what about the oxygen?

00:06:59.379 --> 00:07:02.281
Where's that involvement as an input?

00:07:02.281 --> 00:07:05.915
Well, the oxygen is the
eventual electronic sector

00:07:05.915 --> 00:07:08.113
at the end of the
electron transport chain.

00:07:08.113 --> 00:07:10.546
And not only is it accepting electrons,

00:07:10.546 --> 00:07:12.539
it's accepting hydrogen protons.

00:07:12.539 --> 00:07:17.248
So the oxygen is an input into
the electron transport chain.

00:07:17.248 --> 00:07:20.070
And then once it gets those electrons

00:07:20.070 --> 00:07:21.670
and those hydrogen protons,

00:07:21.670 --> 00:07:23.680
well, you can imagine what the output is.

00:07:23.680 --> 00:07:25.959
You add some oxygen to some
hydrogen protons and electrons,

00:07:25.959 --> 00:07:28.730
you're going to get water.

00:07:28.730 --> 00:07:31.420
You're going to get this
output right over here.

00:07:31.420 --> 00:07:33.460
And what about the carbon dioxide?

00:07:33.460 --> 00:07:34.368
Well, the carbon dioxide

00:07:34.368 --> 00:07:38.713
is going to be an output
of the citric acid cycle.


Cell division and organism growth

WEBVTT
Kind: captions
Language: en

00:00:00.340 --> 00:00:01.310
- [Lecturer] In this
video, we're gonna talk

00:00:01.310 --> 00:00:05.070
about cell division and organism growth.

00:00:05.070 --> 00:00:06.840
Or another way to think about it is,

00:00:06.840 --> 00:00:09.300
how do we start with fertilization?

00:00:09.300 --> 00:00:11.270
And we talk about this in other videos,

00:00:11.270 --> 00:00:14.010
but in sexually reproducing species,

00:00:14.010 --> 00:00:18.140
each individual starts off as a cell

00:00:18.140 --> 00:00:21.010
that is the result of the fusion

00:00:21.010 --> 00:00:24.990
between a sperm and an
egg, between two gametes.

00:00:24.990 --> 00:00:27.550
And each of these gametes have half

00:00:27.550 --> 00:00:31.700
of the genetic material
needed to make that organism.

00:00:31.700 --> 00:00:35.400
So once they fuse, once the
fertilization has happened,

00:00:35.400 --> 00:00:36.670
you are now diploid.

00:00:36.670 --> 00:00:38.570
So you're haploid when you have half

00:00:38.570 --> 00:00:40.860
of the genetic material, as
each of these individually

00:00:40.860 --> 00:00:42.270
have each of these gametes,

00:00:42.270 --> 00:00:45.340
and then you become
diploid once it's fused.

00:00:45.340 --> 00:00:48.370
Well, once it's fused, that fertilized egg

00:00:48.370 --> 00:00:51.840
will then start to divide and replicate.

00:00:51.840 --> 00:00:54.560
And so a short period of time later,

00:00:54.560 --> 00:00:57.310
you might have eight cells
that has divided in two,

00:00:57.310 --> 00:00:58.320
it'll first divide into two,

00:00:58.320 --> 00:00:59.580
then those two will become four,

00:00:59.580 --> 00:01:02.640
those four will become eight,
the eight will become 16,

00:01:02.640 --> 00:01:05.230
and you keep dividing,
and before you know it,

00:01:05.230 --> 00:01:07.210
you have trillions of cells

00:01:07.210 --> 00:01:09.420
on the order of 30 to 40 trillion

00:01:09.420 --> 00:01:11.740
and you could create this
very handsome organism

00:01:11.740 --> 00:01:13.340
right over here.

00:01:13.340 --> 00:01:14.860
But an interesting question is,

00:01:14.860 --> 00:01:16.830
how does that division happen?

00:01:16.830 --> 00:01:18.670
And are the cells identical?

00:01:18.670 --> 00:01:21.180
Do they have the same
identical genetic material?

00:01:21.180 --> 00:01:23.340
But if they are, how do they differentiate

00:01:23.340 --> 00:01:25.100
into all of the different types of cells

00:01:25.100 --> 00:01:26.980
that make this handsome organism?

00:01:26.980 --> 00:01:28.860
The skin cells versus the heart cells

00:01:28.860 --> 00:01:30.320
versus the nerve cells?

00:01:30.320 --> 00:01:32.390
And this process of cell division

00:01:32.390 --> 00:01:36.510
in which a parent cell divides
into two new daughter cells,

00:01:36.510 --> 00:01:39.470
each of which is genetically
identical to the parent cell,

00:01:39.470 --> 00:01:41.603
is known as mitosis.

00:01:42.600 --> 00:01:45.463
And so let's dig into
mitosis a little bit.

00:01:46.360 --> 00:01:48.900
So let's start with two daughter cells

00:01:48.900 --> 00:01:51.590
from a previous round of mitosis.

00:01:51.590 --> 00:01:53.910
Now, this would not be a human cell.

00:01:53.910 --> 00:01:57.600
What we're looking at is four
chromosomes in two pairs.

00:01:57.600 --> 00:01:59.300
And the way that they've color-coded it,

00:01:59.300 --> 00:02:02.590
two of these are blue
and two of these are red.

00:02:02.590 --> 00:02:06.910
While a human cell would have
23 pairs or 46 chromosomes,

00:02:06.910 --> 00:02:08.540
but this is a eukaryotic cell.

00:02:08.540 --> 00:02:10.420
The genetic material is inside

00:02:10.420 --> 00:02:12.660
of the nucleus right over here.

00:02:12.660 --> 00:02:15.970
And just to understand what
these long strands are,

00:02:15.970 --> 00:02:19.790
these are chromosomes in
their non-condensed form.

00:02:19.790 --> 00:02:21.720
And a chromosome you can really view

00:02:21.720 --> 00:02:24.520
as a long strand of DNA,

00:02:24.520 --> 00:02:27.230
and you're going to have
segments of that DNA

00:02:27.230 --> 00:02:29.830
that code for specific proteins,

00:02:29.830 --> 00:02:33.330
and those segments are what we call genes.

00:02:33.330 --> 00:02:35.350
In a given chromosome pair,

00:02:35.350 --> 00:02:38.290
you will code for the same genes,

00:02:38.290 --> 00:02:41.170
but you might have different
versions of the same gene.

00:02:41.170 --> 00:02:42.640
Maybe this gene right over here

00:02:42.640 --> 00:02:45.030
contributes to hair color in some way,

00:02:45.030 --> 00:02:47.710
and then this other one
contributes in the same way,

00:02:47.710 --> 00:02:49.980
but it might lead to a
different hair color.

00:02:49.980 --> 00:02:51.900
So each of these chromosomes in a pair,

00:02:51.900 --> 00:02:54.590
we call them homologous
or homologous pairs.

00:02:54.590 --> 00:02:56.640
They're coding for the same genes.

00:02:56.640 --> 00:02:58.200
They're the same set of genes,

00:02:58.200 --> 00:02:59.610
but they might have different versions

00:02:59.610 --> 00:03:02.360
of those genes or different alleles.

00:03:02.360 --> 00:03:04.010
So that's what we're seeing here.

00:03:04.010 --> 00:03:07.420
Now to prepare for mitosis,
what we need to see

00:03:07.420 --> 00:03:11.220
is each of these chromosomes
need to replicate,

00:03:11.220 --> 00:03:14.920
and once they do, the
cell might look like this.

00:03:14.920 --> 00:03:16.060
Now it's hard to see it here,

00:03:16.060 --> 00:03:18.400
but the two copies that are now replicated

00:03:18.400 --> 00:03:21.740
and connected at the center,
we call them sister chromatids.

00:03:21.740 --> 00:03:23.870
And we can see that a little bit clearer

00:03:23.870 --> 00:03:26.450
in the early phases of mitosis.

00:03:26.450 --> 00:03:29.210
So first, we see that the chromosomes

00:03:29.210 --> 00:03:32.620
have condensed into what
we classically imagine

00:03:32.620 --> 00:03:35.180
as chromosomes when we look
at it into a microscope.

00:03:35.180 --> 00:03:38.180
This is really happening
in preparation for mitosis,

00:03:38.180 --> 00:03:40.520
in preparation for cell division.

00:03:40.520 --> 00:03:43.360
And so you see those two homologous pairs,

00:03:43.360 --> 00:03:46.070
and you can see each of those chromosomes

00:03:46.070 --> 00:03:49.140
actually now consists of
two sister chromatids,

00:03:49.140 --> 00:03:51.810
one over here, one over there.

00:03:51.810 --> 00:03:53.070
As we go through mitosis,

00:03:53.070 --> 00:03:55.710
they're going to separate
into individual chromosomes

00:03:55.710 --> 00:03:58.220
that are actually just
copies of each other.

00:03:58.220 --> 00:03:59.650
Now, the other thing that we're seeing

00:03:59.650 --> 00:04:01.750
in this early phase of mitosis

00:04:01.750 --> 00:04:05.180
is that the nuclear envelope
starts to break down,

00:04:05.180 --> 00:04:06.500
and we're gonna see why that's important,

00:04:06.500 --> 00:04:08.530
because we're gonna have to
separate the chromosomes.

00:04:08.530 --> 00:04:10.160
Now, the other thing that we see,

00:04:10.160 --> 00:04:12.050
and in other future biology classes

00:04:12.050 --> 00:04:13.800
you'll go into much more detail,

00:04:13.800 --> 00:04:17.320
is the mitotic spindle
is starting to form.

00:04:17.320 --> 00:04:19.390
Now, we don't have to
go into all the details

00:04:19.390 --> 00:04:21.510
of the different parts
of the mitotic spindle,

00:04:21.510 --> 00:04:25.010
but imagine a bunch of structures
made primarily by protein

00:04:25.010 --> 00:04:27.300
that are actually going to act to allow

00:04:27.300 --> 00:04:29.990
the mitosis to happen,
to grab the chromosomes,

00:04:29.990 --> 00:04:33.800
to pull them apart, to allow
the cell to change its shape

00:04:33.800 --> 00:04:36.830
so that it will eventually
be able to divide.

00:04:36.830 --> 00:04:41.800
But after that, we go into
the middle phase of mitosis.

00:04:41.800 --> 00:04:44.610
So as we enter into the
middle phases of mitosis,

00:04:44.610 --> 00:04:46.190
we can see now that the chromosomes

00:04:46.190 --> 00:04:47.510
are aligned at the center,

00:04:47.510 --> 00:04:49.490
and they've actually now been attached

00:04:49.490 --> 00:04:51.740
to the mitotic spindle, which
is going to be important,

00:04:51.740 --> 00:04:54.440
because that's the machinery
that's going to pull them apart

00:04:54.440 --> 00:04:57.040
and bring them to the
different sides of the cell.

00:04:57.040 --> 00:04:59.520
And as we continue through
the middle phases of mitosis,

00:04:59.520 --> 00:05:01.340
we see that right over there,

00:05:01.340 --> 00:05:04.340
that those sister chromatids
are now pulled apart

00:05:04.340 --> 00:05:06.380
and they are copies of each other.

00:05:06.380 --> 00:05:08.410
They became copies of
each other back here,

00:05:08.410 --> 00:05:10.180
where the DNA originally replicated

00:05:10.180 --> 00:05:12.470
when it wasn't in its condensed form.

00:05:12.470 --> 00:05:14.290
But I think you see where this is going.

00:05:14.290 --> 00:05:17.150
As the mitotic spindle
pulls on these chromosomes,

00:05:17.150 --> 00:05:20.460
we then enter into the
late phases of mitosis.

00:05:20.460 --> 00:05:23.750
And you can see here that
the sister chromatids,

00:05:23.750 --> 00:05:25.390
which are now individual chromosomes,

00:05:25.390 --> 00:05:29.810
have been pulled to either side
of that now elongated cell.

00:05:29.810 --> 00:05:31.760
You can see that once they're there,

00:05:31.760 --> 00:05:35.850
a nuclear envelope begins to
form again on either side,

00:05:35.850 --> 00:05:38.160
and then the mitotic spindle breaks down

00:05:38.160 --> 00:05:40.520
and the splitting of the cytoplasm finally

00:05:40.520 --> 00:05:44.680
into two daughter cells
is known as cytokinesis.

00:05:44.680 --> 00:05:46.910
So it's pretty mind boggling to realize

00:05:46.910 --> 00:05:49.140
that this is going on in
your body continuously,

00:05:49.140 --> 00:05:51.380
and this is what allowed
all of us to start

00:05:51.380 --> 00:05:54.170
as a single-celled
organism, a fertilized egg,

00:05:54.170 --> 00:05:57.740
and become an organism made
of tens of trillions of cells.

00:05:57.740 --> 00:05:59.900
Now, I haven't gone into detail yet.

00:05:59.900 --> 00:06:01.640
Even though the great
majority of our cells

00:06:01.640 --> 00:06:03.410
have the exact same genetics,

00:06:03.410 --> 00:06:05.400
they are actually able to differentiate,

00:06:05.400 --> 00:06:07.460
express different parts of the genetics

00:06:07.460 --> 00:06:09.820
based on the roles that they need to play,

00:06:09.820 --> 00:06:12.870
but we will talk about
that in future videos.

00:06:12.870 --> 00:06:14.530
It's also important to realize

00:06:14.530 --> 00:06:17.240
that mitosis isn't just
about growing an organism.

00:06:17.240 --> 00:06:19.290
It's also about maintaining an organism

00:06:19.290 --> 00:06:21.760
and doing tissue repair for an organism.

00:06:21.760 --> 00:06:23.010
So I'll leave you there.

00:06:23.010 --> 00:06:24.900
Look at your hands, look at your arms,

00:06:24.900 --> 00:06:26.572
look in the mirror and just realize

00:06:26.572 --> 00:06:31.030
that you are an organism
of 30 to 40 trillion cells

00:06:31.030 --> 00:06:32.590
that all started with one cell

00:06:32.590 --> 00:06:36.023
through many, many,
many rounds of mitosis.


Natural selection and evolution

WEBVTT
Kind: captions
Language: en

00:00:00.224 --> 00:00:02.480
- [Instructor] Many of you
all are probably familiar

00:00:02.480 --> 00:00:04.640
with the term evolution,
and some of you all,

00:00:04.640 --> 00:00:05.820
I'm guessing, are also familiar

00:00:05.820 --> 00:00:08.040
with the term natural selection,
although it isn't used

00:00:08.040 --> 00:00:10.250
quite as much as evolution.

00:00:10.250 --> 00:00:11.550
And what we're going to do in this video

00:00:11.550 --> 00:00:13.980
is see how these are
connected, but we're also

00:00:13.980 --> 00:00:16.640
going to address some
potential misconceptions

00:00:16.640 --> 00:00:19.320
that folks have about evolution.

00:00:19.320 --> 00:00:21.860
So when a lot of people
think of evolution,

00:00:21.860 --> 00:00:23.830
they think of a diagram or an image

00:00:23.830 --> 00:00:25.400
that looks something like this.

00:00:25.400 --> 00:00:27.670
They can see what they
would consider to be

00:00:27.670 --> 00:00:31.190
a more primitive ancestor evolving into

00:00:31.190 --> 00:00:35.810
a more sophisticated, a more
modern type of organism.

00:00:35.810 --> 00:00:38.210
And this is going from
some type of primitive ape,

00:00:38.210 --> 00:00:40.880
all the way to human beings.

00:00:40.880 --> 00:00:43.040
Now there's some aspects of this diagram

00:00:43.040 --> 00:00:47.400
that give the right idea, that
evolution is the phenomenon

00:00:47.400 --> 00:00:50.510
that organisms over time can evolve,

00:00:50.510 --> 00:00:53.640
can change in their
traits, that can actually

00:00:53.640 --> 00:00:55.920
become different species.

00:00:55.920 --> 00:00:57.640
Now the one thing about
this diagram that might

00:00:57.640 --> 00:01:00.840
be misleading is calling
this character primitive

00:01:00.840 --> 00:01:03.140
and somehow imagining
that this one in the front

00:01:03.140 --> 00:01:06.080
is better or more advanced.

00:01:06.080 --> 00:01:07.940
Evolution doesn't necessarily go

00:01:07.940 --> 00:01:10.930
from good to bad or primitive to advanced.

00:01:10.930 --> 00:01:14.030
It's really just continual change based on

00:01:14.030 --> 00:01:16.740
what is most suitable for the environment

00:01:16.740 --> 00:01:18.780
in which the organisms are in.

00:01:18.780 --> 00:01:21.220
And this can take millions of years.

00:01:21.220 --> 00:01:23.990
For example, the common
ancestor of human beings

00:01:23.990 --> 00:01:27.850
and other apes like
chimpanzees or gorillas

00:01:27.850 --> 00:01:31.710
can be five, 10 million-plus
years in the past,

00:01:31.710 --> 00:01:33.900
but it can also happen
right before our eyes.

00:01:33.900 --> 00:01:36.270
For example, every year
we have a new flu virus

00:01:36.270 --> 00:01:39.280
because the flu virus
is constantly evolving

00:01:39.280 --> 00:01:40.990
through mutation.

00:01:40.990 --> 00:01:42.700
We have the Coronavirus and we're having

00:01:42.700 --> 00:01:44.240
new variants of that, it seems like,

00:01:44.240 --> 00:01:45.990
almost every few months.

00:01:45.990 --> 00:01:49.300
That is evolution happening
right before our eyes.

00:01:49.300 --> 00:01:52.780
But the key question is, how
does this actually happen?

00:01:52.780 --> 00:01:55.600
Does the DNA know to
change into something else?

00:01:55.600 --> 00:01:57.840
Well, clearly not. The
DNA is not sentient.

00:01:57.840 --> 00:02:00.310
It is not somehow constructing itself.

00:02:00.310 --> 00:02:03.260
And that's where natural
selection comes into the picture.

00:02:03.260 --> 00:02:06.220
So let's imagine a
population, and I'm gonna

00:02:06.220 --> 00:02:08.180
think about a very abstract population

00:02:08.180 --> 00:02:11.150
of these little circle-shaped things.

00:02:11.150 --> 00:02:13.760
And an important characteristic
for evolution to happen

00:02:13.760 --> 00:02:18.170
is that you need variation
in the population.

00:02:18.170 --> 00:02:20.550
And we talk about variation,
we're talking about

00:02:20.550 --> 00:02:23.677
different expressed
traits, and you might ask,

00:02:23.677 --> 00:02:26.960
"Where does that variation
actually come from?"

00:02:26.960 --> 00:02:29.350
Well, it's going to come from mutation.

00:02:29.350 --> 00:02:31.930
I talked about variation
when we think about viruses,

00:02:31.930 --> 00:02:34.050
the flu virus or the Coronavirus,

00:02:34.050 --> 00:02:36.890
and it can also come
from sexual reproduction,

00:02:36.890 --> 00:02:39.690
and we go into a lot of
detail in other videos

00:02:39.690 --> 00:02:42.940
how sexual reproduction mixes and matches

00:02:42.940 --> 00:02:45.900
all of the potential alleles
that are in a population

00:02:45.900 --> 00:02:47.810
so that different
members of the population

00:02:47.810 --> 00:02:50.370
are getting different
combinations of those alleles,

00:02:50.370 --> 00:02:53.120
and so that contributes to variation.

00:02:53.120 --> 00:02:57.290
And that variation by itself
does not lead to evolution.

00:02:57.290 --> 00:03:00.770
You need variation and selection pressure.

00:03:00.770 --> 00:03:02.307
And this is really where the term

00:03:02.307 --> 00:03:05.170
"natural selection" is coming from.

00:03:05.170 --> 00:03:07.700
What do I mean by selection pressure?

00:03:07.700 --> 00:03:09.720
Well, in this little example here,

00:03:09.720 --> 00:03:13.370
if these circles and
triangle-looking things

00:03:13.370 --> 00:03:15.440
could just keep
reproducing, they could find

00:03:15.440 --> 00:03:19.400
as many resources as they need,
there's no shortage of food,

00:03:19.400 --> 00:03:22.200
there's no shortage of
environments in which they can live

00:03:22.200 --> 00:03:24.610
and reproduce, they had no predators,

00:03:24.610 --> 00:03:26.400
well, you're not gonna
have selection pressure.

00:03:26.400 --> 00:03:29.230
And so all of these variations
might have an equal chance

00:03:29.230 --> 00:03:32.440
of living their life and then reproducing.

00:03:32.440 --> 00:03:34.930
But now let's introduce
some selection pressure

00:03:34.930 --> 00:03:36.740
and imagine what might happen.

00:03:36.740 --> 00:03:38.770
Let's say we introduce
the selection pressure

00:03:38.770 --> 00:03:43.770
of a predator that has a much
easier time seeing white.

00:03:46.810 --> 00:03:48.650
Well, then what's going to happen?

00:03:48.650 --> 00:03:51.050
Well over time, generation to generation,

00:03:51.050 --> 00:03:53.800
the white circles and
triangles here are going to be

00:03:53.800 --> 00:03:56.860
much more likely to be
eaten by that predator

00:03:56.860 --> 00:03:59.860
before they can reproduce
and pass on the allele

00:03:59.860 --> 00:04:03.140
or the alleles that might
result in this white trait,

00:04:03.140 --> 00:04:05.890
and so next generations
or future generations

00:04:05.890 --> 00:04:08.330
are going to have fewer and
fewer of these white shapes,

00:04:08.330 --> 00:04:11.970
so the next generation
might look a lot like this.

00:04:11.970 --> 00:04:15.970
A lot more of the purple we're seeing

00:04:15.970 --> 00:04:20.070
and a lot more of the blue.

00:04:20.070 --> 00:04:22.300
Now on the other hand,
you could have a scenario

00:04:22.300 --> 00:04:24.600
where instead of a
predator that sees white

00:04:24.600 --> 00:04:26.580
and can't see the other colors showing up,

00:04:26.580 --> 00:04:28.630
where there's a shortage of food.

00:04:28.630 --> 00:04:31.440
So that's another form
of selection pressure.

00:04:31.440 --> 00:04:34.360
Let's say a more triangular shape

00:04:34.360 --> 00:04:37.980
is useful for finding food.

00:04:37.980 --> 00:04:40.410
for food.

00:04:40.410 --> 00:04:42.260
Well, then what's going to happen?

00:04:42.260 --> 00:04:44.560
Well, generation by
generation, these shapes

00:04:44.560 --> 00:04:46.830
that are more triangular are going to have

00:04:46.830 --> 00:04:49.200
a better chance of
surviving and reproducing.

00:04:49.200 --> 00:04:52.720
And so maybe in the
first generation you have

00:04:52.720 --> 00:04:55.090
maybe something like that
does reasonably well,

00:04:55.090 --> 00:04:57.300
something like that could do very well.

00:04:57.300 --> 00:04:59.380
Something like that would do well.

00:04:59.380 --> 00:05:01.840
Something like this could do well,

00:05:01.840 --> 00:05:03.320
but we're gonna see, we might see

00:05:03.320 --> 00:05:06.020
a few of the circles still.

00:05:06.020 --> 00:05:08.020
We might see a few of these characters,

00:05:08.020 --> 00:05:09.600
but we'll see fewer have them.

00:05:09.600 --> 00:05:10.840
And we're gonna see more

00:05:11.848 --> 00:05:14.300
of these characters right over here.

00:05:14.300 --> 00:05:16.250
And now you can imagine if this

00:05:16.250 --> 00:05:18.390
environmental pressure continues,

00:05:18.390 --> 00:05:20.330
then over generation and generation,

00:05:20.330 --> 00:05:23.130
you keep selecting for more triangular,

00:05:23.130 --> 00:05:25.940
if you could go forward
many hundreds or thousands

00:05:25.940 --> 00:05:28.200
or hundreds of thousands
or millions of years,

00:05:28.200 --> 00:05:30.480
you might see some
subset of this population

00:05:30.480 --> 00:05:32.550
that lives in this environment.

00:05:32.550 --> 00:05:34.490
They might have a very triangular shape.

00:05:34.490 --> 00:05:37.940
They might not even look
anything like their ancestors.

00:05:37.940 --> 00:05:40.430
Now, does this mean that
this shape right over here

00:05:40.430 --> 00:05:42.800
is somehow more advanced
or better than what

00:05:42.800 --> 00:05:45.770
their ancestors saw, or maybe
there's a cousin species

00:05:45.770 --> 00:05:47.530
that was where the predators see white

00:05:47.530 --> 00:05:49.940
and the triangular shape
really doesn't help you,

00:05:49.940 --> 00:05:52.600
and so they have a cousin
species that looks like this.

00:05:52.600 --> 00:05:54.300
There's no way of saying that this species

00:05:54.300 --> 00:05:56.360
is more advanced or
better than this species,

00:05:56.360 --> 00:05:59.960
but what we can say is, it is
more fit for its environment.

00:05:59.960 --> 00:06:02.800
And this species is more
fit in its environment.

00:06:02.800 --> 00:06:04.850
So I will leave you there,
and it's important to realize

00:06:04.850 --> 00:06:06.570
this isn't some magical process.

00:06:06.570 --> 00:06:08.950
It's all due to variation
caused by mutation

00:06:08.950 --> 00:06:11.710
and sexual reproduction,
selection pressure,

00:06:11.710 --> 00:06:13.790
and then that change happens over time.

00:06:13.790 --> 00:06:15.670
And this isn't just something that happens

00:06:15.670 --> 00:06:17.900
over millions or tens
of millions of years.

00:06:17.900 --> 00:06:20.630
It happens before our eyes every day.

00:06:20.630 --> 00:06:22.830
When we talk about the
different flu strain

00:06:22.830 --> 00:06:24.620
or a different coronavirus strain

00:06:24.620 --> 00:06:26.520
or drug-resistant bacteria,

00:06:26.520 --> 00:06:29.393
it's very relevant to
our day-to-day lives.


Genes, traits, and the environment

WEBVTT
Kind: captions
Language: en

00:00:00.480 --> 00:00:03.830
- [Instructor] This is a
prize-winning Himalayan rabbit,

00:00:03.830 --> 00:00:06.850
and it will help us see
that an organism's traits

00:00:06.850 --> 00:00:10.190
aren't only the results
of which genes they have,

00:00:10.190 --> 00:00:12.750
but also which environmental factors

00:00:12.750 --> 00:00:14.610
the organism is exposed to.

00:00:14.610 --> 00:00:16.580
So we're gonna look at a specific gene

00:00:16.580 --> 00:00:20.830
in the Himalayan rabbit
known as the C-gene,

00:00:20.830 --> 00:00:24.110
and to C-gene encodes a
protein which acts as an enzyme

00:00:24.110 --> 00:00:26.150
in the eventual production of pigment.

00:00:26.150 --> 00:00:29.550
And we can see where that
enzyme is more active,

00:00:29.550 --> 00:00:34.130
at the nose, on the feet,
on the ears right over here,

00:00:34.130 --> 00:00:37.180
and then you could also
see that it is inactive

00:00:37.180 --> 00:00:40.410
across the body and in
some parts of the head

00:00:40.410 --> 00:00:41.900
right over here.

00:00:41.900 --> 00:00:44.620
Now the question is
what's causing it to be

00:00:44.620 --> 00:00:46.890
inactive or active?

00:00:46.890 --> 00:00:50.510
Well, it turns out that the
enzyme that the C-gene codes for

00:00:50.510 --> 00:00:55.030
is optimally active at 15 degrees Celsius

00:00:55.030 --> 00:00:57.710
to 25 degrees Celsius,

00:00:57.710 --> 00:01:00.810
and this alone can actually explain

00:01:00.810 --> 00:01:02.700
the difference in pigmentation.

00:01:02.700 --> 00:01:04.120
How does that make sense?

00:01:04.120 --> 00:01:06.390
Well imagine that this rabbit over here

00:01:06.390 --> 00:01:10.350
was raised at 20 degrees Celsius.

00:01:10.350 --> 00:01:12.950
The body itself, it's a
mammal, it's warm blooded,

00:01:12.950 --> 00:01:15.120
it's going to be producing heat.

00:01:15.120 --> 00:01:20.120
So the body, this area right
over here, is going to be warm.

00:01:21.800 --> 00:01:25.080
And so, over here where we're
going to be greater than,

00:01:25.080 --> 00:01:27.800
let's say 35 degrees Celsius,

00:01:27.800 --> 00:01:30.870
where the enzyme that the C-gene
and codes for is inactive.

00:01:30.870 --> 00:01:32.420
This is where it's optimally active,

00:01:32.420 --> 00:01:34.340
and above 35 degrees Celsius

00:01:34.340 --> 00:01:36.700
it's actually not active at all.

00:01:36.700 --> 00:01:39.830
And once again, why is
it so warm over here?

00:01:39.830 --> 00:01:41.440
It's not just the ambient temperature.

00:01:41.440 --> 00:01:43.370
It's the combination of
the ambient temperature

00:01:43.370 --> 00:01:46.010
plus the heat from the rabbit itself.

00:01:46.010 --> 00:01:48.930
Now, if you go at some
of the further off parts

00:01:48.930 --> 00:01:49.860
of the rabbit's body,

00:01:49.860 --> 00:01:51.690
and this is actually true
of our bodies as well,

00:01:51.690 --> 00:01:54.020
if you go to the ears, you go to the nose,

00:01:54.020 --> 00:01:58.040
you go to the feet, you
have less body warmth.

00:01:58.040 --> 00:02:03.040
And so, it is going to be cooler
in these parts of the body,

00:02:03.700 --> 00:02:04.710
and it could be cool enough

00:02:04.710 --> 00:02:06.810
so that the protein encoded by the C-gene

00:02:06.810 --> 00:02:08.260
is actually active.

00:02:08.260 --> 00:02:10.260
And so, you see something very simple

00:02:10.260 --> 00:02:12.030
can create this very neat

00:02:12.030 --> 00:02:15.860
and, I would have to say,
cute pattern as well.

00:02:15.860 --> 00:02:17.920
Now, some of you might be wondering, well,

00:02:17.920 --> 00:02:20.020
could I then based on temperature,

00:02:20.020 --> 00:02:23.070
raise a completely white Himalayan rabbit,

00:02:23.070 --> 00:02:24.710
and the answer is yes.

00:02:24.710 --> 00:02:26.470
If you had a twin of this rabbit

00:02:26.470 --> 00:02:28.210
and you raised it in an environment

00:02:28.210 --> 00:02:32.140
that was, say, hotter
than 30 degrees Celsius,

00:02:32.140 --> 00:02:35.330
well then all of its
body would probably be

00:02:35.330 --> 00:02:38.320
of a temperature where the
protein encoded by the C-gene is

00:02:38.320 --> 00:02:40.570
not too active or not active at all,

00:02:40.570 --> 00:02:42.150
and it would be a white rabbit.

00:02:42.150 --> 00:02:44.190
And people have performed this experiment

00:02:44.190 --> 00:02:47.940
over 100 years ago and
they saw that exact result.

00:02:47.940 --> 00:02:50.470
And temperature is just
one of many factors.

00:02:50.470 --> 00:02:52.250
So there's research where
they're able to make

00:02:52.250 --> 00:02:54.400
a Cyclops fish, a fish with one eye,

00:02:54.400 --> 00:02:57.550
based on chemicals and
where it was reared.

00:02:57.550 --> 00:03:00.410
There's experiments with
the light that depending on

00:03:00.410 --> 00:03:02.270
the light or the lack of light,

00:03:02.270 --> 00:03:03.410
at the caterpillar stage,

00:03:03.410 --> 00:03:05.750
it can affect what the
butterfly looks like

00:03:05.750 --> 00:03:07.630
when it develops wings.

00:03:07.630 --> 00:03:10.710
Food can activate or
inactivate certain genes,

00:03:10.710 --> 00:03:13.410
not just in other animals,
but even in our own bodies.

00:03:13.410 --> 00:03:16.550
There's research around fasting
and how that might activate

00:03:16.550 --> 00:03:18.880
or inactivate certain genes.

00:03:18.880 --> 00:03:20.400
Stress can affect genes.

00:03:20.400 --> 00:03:22.150
Hormones can affect genes.

00:03:22.150 --> 00:03:24.880
So the big takeaway here
is an organism's traits

00:03:24.880 --> 00:03:28.480
are not just due to which
genes the organism has,

00:03:28.480 --> 00:03:32.353
but are influenced by
environmental factors as well.


Gene expression and regulation

WEBVTT
Kind: captions
Language: en

00:00:00.950 --> 00:00:02.790
- [Instructor] By now
you're likely familiar

00:00:02.790 --> 00:00:07.240
with the idea that DNA,
deoxyribonucleic acid,

00:00:07.240 --> 00:00:10.340
is the molecular basis of inheritance.

00:00:10.340 --> 00:00:12.090
You might also have a sense

00:00:12.090 --> 00:00:15.190
that it is somehow
involved with chromosomes.

00:00:15.190 --> 00:00:18.120
And in this video, I wanna make
sure we can connect the dots

00:00:18.120 --> 00:00:19.940
with all of these concepts that we have

00:00:19.940 --> 00:00:21.440
when we come to genetics.

00:00:21.440 --> 00:00:22.670
What's a chromosome.

00:00:22.670 --> 00:00:24.750
How does it relate to DNA?

00:00:24.750 --> 00:00:27.050
How does that relate to genes?

00:00:27.050 --> 00:00:29.160
And then how do genes and DNA

00:00:29.160 --> 00:00:32.030
relate to proteins or other things?

00:00:32.030 --> 00:00:33.820
Well, as you can see in this diagram

00:00:33.820 --> 00:00:37.420
from the National Human
Genome Research Institute,

00:00:37.420 --> 00:00:39.210
they're showing us a blown up cell.

00:00:39.210 --> 00:00:41.280
So this is the outer membrane of the cell

00:00:41.280 --> 00:00:42.690
that you see right over here.

00:00:42.690 --> 00:00:47.660
And in here, they are showing
us the nucleus of the cell.

00:00:47.660 --> 00:00:52.660
And inside the nucleus of
eukaryotes, you have your DNA.

00:00:53.010 --> 00:00:54.480
Now, the way that they have shown it,

00:00:54.480 --> 00:00:58.040
the DNA all looks like
these Xes over here.

00:00:58.040 --> 00:00:59.150
Now, it's important to realize

00:00:59.150 --> 00:01:03.110
that DNA isn't always in this
condensed chromosome form.

00:01:03.110 --> 00:01:04.540
When DNA replicates,

00:01:04.540 --> 00:01:07.620
it is in it's loose or uncondensed form.

00:01:07.620 --> 00:01:11.640
When it condenses, maybe in
preparation for say mitosis,

00:01:11.640 --> 00:01:14.790
then it takes on an X shape.

00:01:14.790 --> 00:01:18.620
But this X actually has two
copies of the same chromosome.

00:01:18.620 --> 00:01:19.930
But while they are connected,

00:01:19.930 --> 00:01:22.050
consider that to be one chromosome.

00:01:22.050 --> 00:01:24.670
But then once they separate,
say during mitosis,

00:01:24.670 --> 00:01:27.530
then people would consider
it to be two chromosomes.

00:01:27.530 --> 00:01:29.910
Now, if we look at chromosomes
under a microscope,

00:01:29.910 --> 00:01:32.490
you might see something like this.

00:01:32.490 --> 00:01:34.640
As you notice, they come in pairs.

00:01:34.640 --> 00:01:36.170
And this is actually what chromosomes

00:01:36.170 --> 00:01:37.770
would look like for the human genome.

00:01:37.770 --> 00:01:39.420
You have 23 pairs.

00:01:39.420 --> 00:01:41.810
The way we know that
this is a biological male

00:01:41.810 --> 00:01:43.610
is by looking right over here.

00:01:43.610 --> 00:01:45.790
This short little
chromosome right over here,

00:01:45.790 --> 00:01:48.070
that is the Y chromosome.

00:01:48.070 --> 00:01:49.590
And you can see each of these pairs

00:01:49.590 --> 00:01:51.690
have what are called
homologous chromosomes,

00:01:51.690 --> 00:01:53.970
which we've talked about in other videos.

00:01:53.970 --> 00:01:57.000
But it's the view that
these two chromosomes

00:01:57.000 --> 00:01:59.390
code for the same genes,

00:01:59.390 --> 00:02:02.280
but they might have different
versions of the genes on them.

00:02:02.280 --> 00:02:06.370
You get one of the homologous
pair from your female parent,

00:02:06.370 --> 00:02:09.790
and one of the homologous
pair from your male parent.

00:02:09.790 --> 00:02:12.550
And we've gone into some
depth into other videos.

00:02:12.550 --> 00:02:14.380
Now, it's hard to see
it at this resolution,

00:02:14.380 --> 00:02:15.213
but in this image,

00:02:15.213 --> 00:02:17.290
each chromosome has been replicated

00:02:17.290 --> 00:02:20.510
and is actually two copies
connected at the centromere.

00:02:20.510 --> 00:02:21.850
If we were to spread it out,

00:02:21.850 --> 00:02:25.300
it would have that X
shape right over there.

00:02:25.300 --> 00:02:29.080
Now, the question is how does
a chromosome relate to DNA?

00:02:29.080 --> 00:02:32.280
And you can see it in this
broader diagram right over here.

00:02:32.280 --> 00:02:33.990
A chromosome is actually just a very,

00:02:33.990 --> 00:02:37.240
very long strand of DNA
that's all wrapped up.

00:02:37.240 --> 00:02:38.690
And there some other molecules

00:02:38.690 --> 00:02:39.930
and proteins that are involved,

00:02:39.930 --> 00:02:42.010
like histones like you
see right over here.

00:02:42.010 --> 00:02:43.800
that help package the DNA,

00:02:43.800 --> 00:02:46.910
but that's all a chromosome really is.

00:02:46.910 --> 00:02:48.780
In the entire human genome,

00:02:48.780 --> 00:02:53.780
we have 3.2 billion base pairs in our DNA.

00:02:54.720 --> 00:02:56.980
And just as a reminder,
a base pair you can view

00:02:56.980 --> 00:02:59.550
as each of the rungs of this ladder.

00:02:59.550 --> 00:03:03.210
Now, those 3.2 billion base pairs,

00:03:03.210 --> 00:03:07.360
they are divided into these 46 chromosomes

00:03:07.360 --> 00:03:09.520
in a complete human genome.

00:03:09.520 --> 00:03:10.520
So you're looking at the order

00:03:10.520 --> 00:03:12.610
of tens to hundreds of millions

00:03:12.610 --> 00:03:15.140
of base pairs per chromosome.

00:03:15.140 --> 00:03:16.720
Now you're probably
familiar with this idea

00:03:16.720 --> 00:03:18.090
that the genes on the DNA

00:03:18.090 --> 00:03:20.060
are actually what code for protein.

00:03:20.060 --> 00:03:21.720
And that is indeed the case.

00:03:21.720 --> 00:03:25.250
If you have a long strand
of DNA right over here,

00:03:25.250 --> 00:03:27.410
not all of it is protein coding,

00:03:27.410 --> 00:03:30.000
but you have protein coding genes on it.

00:03:30.000 --> 00:03:32.330
And if you look at the
entire human genome,

00:03:32.330 --> 00:03:37.330
you're looking at about 20,000
plus protein coding genes,

00:03:38.300 --> 00:03:39.310
each of which is made up

00:03:39.310 --> 00:03:41.710
an average of about 3000 base pairs,

00:03:41.710 --> 00:03:42.810
but it can vary a lot

00:03:42.810 --> 00:03:44.440
depending on the gene you're looking at.

00:03:44.440 --> 00:03:47.710
And the way that we go from
these protein coding genes,

00:03:47.710 --> 00:03:50.140
which are really just sections of the DNA

00:03:50.140 --> 00:03:52.600
on these chromosomes, to proteins,

00:03:52.600 --> 00:03:56.830
this idea is known as the
central dogma of biology

00:03:56.830 --> 00:04:00.000
or oftentimes the central
dogma of molecular biology.

00:04:00.000 --> 00:04:04.120
So this is a chain of DNA
in a protein coding gene.

00:04:04.120 --> 00:04:07.250
The process of transcription
is what takes us

00:04:07.250 --> 00:04:10.780
from one half of this to an mRNA strand,

00:04:10.780 --> 00:04:13.840
which you can view as a
cousin molecule of DNA.

00:04:13.840 --> 00:04:16.340
Now, messenger RNA in particular,

00:04:16.340 --> 00:04:18.670
that then goes to the ribosomes.

00:04:18.670 --> 00:04:20.590
It goes outside of the
nucleus of the cell,

00:04:20.590 --> 00:04:21.690
goes to the ribosomes.

00:04:21.690 --> 00:04:24.110
We talk about this in some
depth in other videos.

00:04:24.110 --> 00:04:25.840
And then at the ribosomes,

00:04:25.840 --> 00:04:29.360
that information is used to
actually construct proteins

00:04:29.360 --> 00:04:30.540
out of amino acids.

00:04:30.540 --> 00:04:32.470
And then those proteins,
those amino acids,

00:04:32.470 --> 00:04:33.450
will interact with each other

00:04:33.450 --> 00:04:35.750
and they'll form a shape of some protein

00:04:35.750 --> 00:04:38.770
that is valuable in the human body.

00:04:38.770 --> 00:04:40.220
Now, what's interesting

00:04:40.220 --> 00:04:44.380
is that even though we most
associate DNA with genes

00:04:44.380 --> 00:04:46.730
that code for proteins in this way,

00:04:46.730 --> 00:04:51.730
the reality is that only 1-2%
of DNA codes for proteins.

00:04:53.230 --> 00:04:54.610
So a natural question would be,

00:04:54.610 --> 00:04:58.710
what is the other 98-99% of DNA doing?

00:04:58.710 --> 00:05:01.310
And that's actually an
active area of research,

00:05:01.310 --> 00:05:03.110
but we have some good ideas.

00:05:03.110 --> 00:05:05.230
We know that some of that DNA

00:05:05.230 --> 00:05:08.910
helps regulate the coding of other DNA.

00:05:08.910 --> 00:05:10.920
What's interesting about the human genome,

00:05:10.920 --> 00:05:12.820
or actually the genome of any organism,

00:05:12.820 --> 00:05:15.970
is that nearly every
cell in the human body

00:05:15.970 --> 00:05:18.660
has this same set of chromosomes,

00:05:18.660 --> 00:05:21.340
has all of the information necessary

00:05:21.340 --> 00:05:24.480
to code for all of the proteins
that any cell might need.

00:05:24.480 --> 00:05:26.100
Exceptions are red blood cells,

00:05:26.100 --> 00:05:27.950
which lose their genetic material,

00:05:27.950 --> 00:05:30.040
and gametes, sperm, or egg cells,

00:05:30.040 --> 00:05:31.810
which have half of the genetic material,

00:05:31.810 --> 00:05:34.410
but almost every other cell
has all the genetic material.

00:05:34.410 --> 00:05:36.080
But obviously cells are different.

00:05:36.080 --> 00:05:38.070
Heart cells are different than neurons,

00:05:38.070 --> 00:05:39.860
which are different than skin cells.

00:05:39.860 --> 00:05:41.100
So a lot of the other DNA

00:05:41.100 --> 00:05:43.520
is part of the regulatory mechanism

00:05:43.520 --> 00:05:45.660
of which genes to express,

00:05:45.660 --> 00:05:48.550
which genes should be coded into proteins

00:05:48.550 --> 00:05:50.050
and which ones should not,

00:05:50.050 --> 00:05:53.060
as we have different types of
cells doing different things.

00:05:53.060 --> 00:05:56.730
And so this is known as
differential gene expression.

00:05:56.730 --> 00:05:58.620
And those parts of the DNA

00:05:58.620 --> 00:06:01.490
that aren't coding directly for proteins,

00:06:01.490 --> 00:06:04.470
we would call those
regulatory sections of DNA.

00:06:04.470 --> 00:06:06.920
Now, there's other stretches of DNA

00:06:06.920 --> 00:06:08.950
that instead of producing mRNA,

00:06:08.950 --> 00:06:12.210
which then gets translated
into polypeptides,

00:06:12.210 --> 00:06:14.360
it could code for other types of RNA,

00:06:14.360 --> 00:06:16.280
which we would call functional RNA

00:06:16.280 --> 00:06:18.810
because that type of
RNA is directly useful.

00:06:18.810 --> 00:06:21.780
It has a function. It's not
just transmitting information.

00:06:21.780 --> 00:06:24.020
For example, you have ribosomal RNA,

00:06:24.020 --> 00:06:26.690
which can be directly
transcribed from DNA,

00:06:26.690 --> 00:06:29.070
and it's used to make up
parts of the ribosome.

00:06:29.070 --> 00:06:30.820
You might've seen transfer RNA

00:06:30.820 --> 00:06:32.620
when we learned about translation.

00:06:32.620 --> 00:06:35.810
They're also involved in the
construction of proteins.

00:06:35.810 --> 00:06:37.000
So I will leave you there.

00:06:37.000 --> 00:06:38.500
Hopefully this connects the dots

00:06:38.500 --> 00:06:41.910
between the idea that most of
your cells in the human body,

00:06:41.910 --> 00:06:44.400
and we're talking about
tens of trillions of cells,

00:06:44.400 --> 00:06:49.320
have the entire complement
of 3.2 billion base pairs

00:06:49.320 --> 00:06:51.920
that are in these 46 chromosomes

00:06:51.920 --> 00:06:54.870
that are organized in 23 pairs

00:06:54.870 --> 00:06:57.730
that contain these 20,000+ genes,

00:06:57.730 --> 00:07:01.040
which only make up 1-2% of the base pairs.

00:07:01.040 --> 00:07:03.120
The rest we're still exploring,

00:07:03.120 --> 00:07:06.210
but it can be involved in
functional RNA and regulation,

00:07:06.210 --> 00:07:07.750
which helps different cells

00:07:07.750 --> 00:07:10.493
do different things at different times.


Stratospheric Ozone Depletion

WEBVTT
Kind: captions
Language: en

00:00:00.490 --> 00:00:01.710
- In this video we're gonna talk about

00:00:01.710 --> 00:00:04.450
a molecule known as Ozone.

00:00:04.450 --> 00:00:07.930
And Ozone you can also view as O3,

00:00:07.930 --> 00:00:10.230
or three oxygens bonded this way,

00:00:10.230 --> 00:00:12.260
these dash lines show that sometimes

00:00:12.260 --> 00:00:13.600
the double bond is on this side,

00:00:13.600 --> 00:00:14.940
sometimes it's on that side.

00:00:14.940 --> 00:00:17.290
You might recognize that as resonance

00:00:17.290 --> 00:00:18.530
in molecular structures,

00:00:18.530 --> 00:00:20.530
or resonance in bonds.

00:00:20.530 --> 00:00:23.630
But it plays some very interesting roles.

00:00:23.630 --> 00:00:27.260
It can both protect
us, and it can hurt us.

00:00:27.260 --> 00:00:30.636
And to understand this,
let's look at this diagram

00:00:30.636 --> 00:00:32.880
of the atmosphere.

00:00:32.880 --> 00:00:34.900
So there's a lot of really interesting

00:00:34.900 --> 00:00:36.470
information in this diagram.

00:00:36.470 --> 00:00:38.360
Some of it relevant to
this video, some of it not,

00:00:38.360 --> 00:00:39.550
but I encourage you to look at it.

00:00:39.550 --> 00:00:41.460
There's all sorts of cool things,

00:00:41.460 --> 00:00:44.500
how temperature changes as
we increase in altitude.

00:00:44.500 --> 00:00:48.030
We see the labels of the major
layers of the atmosphere,

00:00:48.030 --> 00:00:51.040
we can compare it to Mount
Everest and where clouds are.

00:00:51.040 --> 00:00:54.170
But we see a few things,
we have a troposphere,

00:00:54.170 --> 00:00:57.210
and then above that we
have a stratosphere.

00:00:57.210 --> 00:00:59.910
Now in the stratosphere we see this thing

00:00:59.910 --> 00:01:02.990
known as an Ozone layer,

00:01:02.990 --> 00:01:07.990
which is 10 to 20 miles above
the surface of the earth.

00:01:08.120 --> 00:01:12.870
And Ozone in this part of
the atmosphere protects us.

00:01:12.870 --> 00:01:14.610
How does it protect us?

00:01:14.610 --> 00:01:18.210
Well the sun, which most
of us consider our friend,

00:01:18.210 --> 00:01:21.530
that lives 93 million miles away,

00:01:21.530 --> 00:01:24.420
we know that life wouldn't
exist without the sun.

00:01:24.420 --> 00:01:26.540
Most of the energy we have on this planet

00:01:26.540 --> 00:01:28.260
is because of the sun.

00:01:28.260 --> 00:01:32.070
But UV frequencies from the sun,

00:01:32.070 --> 00:01:33.150
if they aren't blocked,

00:01:33.150 --> 00:01:35.030
or if they aren't mitigated a little bit,

00:01:35.030 --> 00:01:36.800
they can cause a lot of damage.

00:01:36.800 --> 00:01:39.980
They have a lot of energy,
they can affect molecules,

00:01:39.980 --> 00:01:43.920
and in particular, they
can affect our DNA.

00:01:43.920 --> 00:01:46.050
And if you start messing with DNA,

00:01:46.050 --> 00:01:50.800
start mutating DNA, that can
lead to things like cancer.

00:01:50.800 --> 00:01:53.350
And so you can imagine, we human beings,

00:01:53.350 --> 00:01:55.020
and actually most organisms

00:01:55.020 --> 00:01:58.640
can only deal with a
certain amount of UV light.

00:01:58.640 --> 00:02:01.240
Now if we had no Ozone layer,

00:02:01.240 --> 00:02:04.260
a lot of that UV light
would come in unchecked.

00:02:04.260 --> 00:02:05.630
It's going to get absorbed a little bit

00:02:05.630 --> 00:02:07.610
by the various layers of the atmosphere,

00:02:07.610 --> 00:02:10.330
but it turns out that Ozone in particular

00:02:10.330 --> 00:02:13.730
is good at protecting us from UV light.

00:02:13.730 --> 00:02:16.420
So if we didn't have this
Ozone layer above us,

00:02:16.420 --> 00:02:18.020
you would see cancer rates go up.

00:02:18.020 --> 00:02:21.323
We would just get a lot more UV energy.

00:02:22.400 --> 00:02:23.640
Now an interesting question is,

00:02:23.640 --> 00:02:26.090
how does this Ozone layer form?

00:02:26.090 --> 00:02:28.570
We're not used to seeing
oxygen in this form.

00:02:28.570 --> 00:02:31.010
Most of the oxygen that
we see in our atmosphere

00:02:31.010 --> 00:02:35.236
is molecular oxygen in
the form of two oxygens

00:02:35.236 --> 00:02:37.500
which looks like that.

00:02:37.500 --> 00:02:39.770
Well is turns out that UV light

00:02:39.770 --> 00:02:41.840
actually helps create the thing

00:02:41.840 --> 00:02:43.910
that protects us from UV light.

00:02:43.910 --> 00:02:46.590
Because O2 in the presence of UV

00:02:46.590 --> 00:02:50.630
can be broken up and
then reformed as Ozone.

00:02:50.630 --> 00:02:51.500
So it's actually the fact

00:02:51.500 --> 00:02:54.050
that you have so much UV light up here,

00:02:54.050 --> 00:02:56.350
that it reacts with oxygen that has raised

00:02:56.350 --> 00:02:57.370
to the stratosphere,

00:02:57.370 --> 00:03:00.940
and some of that gets formed into Ozone.

00:03:00.940 --> 00:03:03.250
Now Ozone is very reactive,

00:03:03.250 --> 00:03:04.530
and it can be a little bit delicate,

00:03:04.530 --> 00:03:06.360
it has a very short half life.

00:03:06.360 --> 00:03:08.413
It is way less stable than O2.

00:03:09.710 --> 00:03:13.030
And so it has to keep getting
replenished in the atmosphere.

00:03:13.030 --> 00:03:15.380
And we also know that certain chemicals

00:03:15.380 --> 00:03:16.910
that we human beings have produced,

00:03:16.910 --> 00:03:18.640
in particular what's often known

00:03:18.640 --> 00:03:20.520
as chlorofloro carbons,

00:03:20.520 --> 00:03:22.910
that's just a fancy
way of saying molecules

00:03:22.910 --> 00:03:24.080
that are hydrocarbons,

00:03:24.080 --> 00:03:25.790
so a bunch of carbons and hydrogens,

00:03:25.790 --> 00:03:28.620
that also involve chlorine and fluorine.

00:03:28.620 --> 00:03:30.690
And these molecules were generated

00:03:30.690 --> 00:03:32.240
in industrial applications,

00:03:32.240 --> 00:03:35.520
things like aerosol
sprays used to have CFCs,

00:03:35.520 --> 00:03:38.900
but it turns out that CFCs
will deplete the ozone layer.

00:03:38.900 --> 00:03:41.670
They'll come up from our
little spray paint cans

00:03:41.670 --> 00:03:44.470
and they'll interact with the
Ozone, and they'll deplete it

00:03:44.470 --> 00:03:45.740
which is not a good thing.

00:03:45.740 --> 00:03:48.330
Once again it will make
us all more susceptible

00:03:48.330 --> 00:03:50.600
to things like cancer.

00:03:50.600 --> 00:03:52.290
Now everything we've talked about so far

00:03:52.290 --> 00:03:55.000
is Ozone in the stratosphere,

00:03:55.000 --> 00:03:56.330
but it turns out that Ozone

00:03:56.330 --> 00:03:59.300
can actually also form
lower in the atmosphere,

00:03:59.300 --> 00:04:01.920
in the place where we
tend to spend our lives,

00:04:01.920 --> 00:04:03.600
in the troposphere.

00:04:03.600 --> 00:04:07.380
And when Ozone is down there,
it's actually a bad thing.

00:04:07.380 --> 00:04:10.400
And to understand why it
might form down there,

00:04:10.400 --> 00:04:11.830
we need to understand the role

00:04:11.830 --> 00:04:13.850
once again that we're playing.

00:04:13.850 --> 00:04:16.920
Nitrous oxides are formed
from automobile exhaust,

00:04:16.920 --> 00:04:18.570
and coal-fired power plants,

00:04:18.570 --> 00:04:21.210
and when those in the
presence of UV light,

00:04:21.210 --> 00:04:24.320
and what's known as
volatile organic compounds,

00:04:24.320 --> 00:04:26.810
which is just a fancy way
of saying organic compounds

00:04:26.810 --> 00:04:28.000
that evaporate very easily,

00:04:28.000 --> 00:04:31.120
and most of these are
naturally produced, the VOCs,

00:04:31.120 --> 00:04:33.500
but when you have the
UV light in conjunction

00:04:33.500 --> 00:04:35.010
with the exhaust from automobiles

00:04:35.010 --> 00:04:37.650
and nitrous oxides from
coal-fired power plants,

00:04:37.650 --> 00:04:40.880
it can produce Ozone in
the lower atmosphere.

00:04:40.880 --> 00:04:43.890
And Ozone as I mentioned
is highly reactive,

00:04:43.890 --> 00:04:45.370
it can damage living tissue,

00:04:45.370 --> 00:04:47.690
it can damage our respiratory systems,

00:04:47.690 --> 00:04:49.730
so you don't want Ozone around.

00:04:49.730 --> 00:04:51.820
So it's good in the upper atmosphere,

00:04:51.820 --> 00:04:54.960
and it is bad in the lower atmosphere.

00:04:54.960 --> 00:04:56.390
So I will leave you there,

00:04:56.390 --> 00:04:58.430
you got your primer on Ozone,

00:04:58.430 --> 00:05:00.220
and just recognize the same thing

00:05:00.220 --> 00:05:01.670
that can help us in one place,

00:05:01.670 --> 00:05:03.530
can hurt us in another place.

00:05:03.530 --> 00:05:05.800
And the same thing that
it's protecting us from

00:05:05.800 --> 00:05:08.753
can actually help create
it, that UV light.