Krebs / citric acid cycle

WEBVTT
Kind: captions
Language: en

00:00:00.710 --> 00:00:03.360
So we already know that if we
start off with a glucose

00:00:03.360 --> 00:00:12.240
molecule, which is a 6-carbon
molecule, that this

00:00:12.240 --> 00:00:15.880
essentially gets split in half
by glycolysis and we end up 2

00:00:15.880 --> 00:00:19.760
pyruvic acids or two
pyruvate molecules.

00:00:19.760 --> 00:00:23.230
So glycolysis literally
splits this in half.

00:00:23.230 --> 00:00:25.200
It lyses the glucose.

00:00:25.200 --> 00:00:29.770
We end up with two pyruvates
or pyruvic acids.

00:00:29.770 --> 00:00:35.350
ruby And these are 3-carbon
molecules.

00:00:35.350 --> 00:00:36.580
There's obviously a
lot of other stuff

00:00:36.580 --> 00:00:37.480
going on in the carbons.

00:00:37.480 --> 00:00:39.470
You saw it in the past. And
you could look up their

00:00:39.470 --> 00:00:42.210
chemical structures on the
internet or on Wikipedia and

00:00:42.210 --> 00:00:42.940
see them in detail.

00:00:42.940 --> 00:00:44.220
But this is kind of the
important thing.

00:00:44.220 --> 00:00:46.770
Is that it was lysed,
it was cut in half.

00:00:46.770 --> 00:00:48.020
And this is what happened
in glycolysis.

00:00:54.020 --> 00:00:56.650
And this happened in the
absence of oxygen.

00:00:56.650 --> 00:00:57.210
Or not necessarily.

00:00:57.210 --> 00:01:00.860
It can happen in the presence
or in the absence of oxygen.

00:01:00.860 --> 00:01:02.520
It doesn't need oxygen.

00:01:02.520 --> 00:01:04.420
And we got a net payoff
of two ATPs.

00:01:08.500 --> 00:01:11.270
And I always say the net there,
because remember, it

00:01:11.270 --> 00:01:14.980
used two ATPs in that investment
stage, and then it

00:01:14.980 --> 00:01:16.060
generated four.

00:01:16.060 --> 00:01:18.980
So on a net basis, it generated
four, used two, it

00:01:18.980 --> 00:01:20.790
gave us two ATPs.

00:01:20.790 --> 00:01:22.580
And it also produced
two NADHs.

00:01:28.160 --> 00:01:30.540
That's what we got out
of glycolysis.

00:01:30.540 --> 00:01:33.160
And just so you can visualize
this a little bit better, let

00:01:33.160 --> 00:01:35.610
me draw a cell right here.

00:01:35.610 --> 00:01:38.520
Maybe I'll draw it down here.

00:01:38.520 --> 00:01:41.340
Let's say I have a cell.

00:01:41.340 --> 00:01:44.010
That's its outer membrane.

00:01:44.010 --> 00:01:45.460
Maybe its nucleus, we're
dealing with

00:01:45.460 --> 00:01:47.000
a eukaryotic cell.

00:01:47.000 --> 00:01:48.400
That doesn't have
to be the case.

00:01:48.400 --> 00:01:50.780
It has its DNA and its chromatin
form all spread

00:01:50.780 --> 00:01:52.040
around like that.

00:01:52.040 --> 00:01:53.490
And then you have
mitochondria.

00:01:53.490 --> 00:01:56.000
And there's a reason why people
call it the power

00:01:56.000 --> 00:01:56.810
centers of the cell.

00:01:56.810 --> 00:01:58.610
We'll look at that
in a second.

00:01:58.610 --> 00:01:59.290
So there's a mitochondria.

00:01:59.290 --> 00:02:01.100
It has an outer membrane
and an inner

00:02:01.100 --> 00:02:03.370
membrane just like that.

00:02:03.370 --> 00:02:05.820
I'll do more detail on the
structure of a mitochondria,

00:02:05.820 --> 00:02:07.380
maybe later in this video
or maybe I'll do a

00:02:07.380 --> 00:02:08.800
whole video on them.

00:02:08.800 --> 00:02:12.870
That's another mitochondria
right there.

00:02:12.870 --> 00:02:15.120
And then all of this fluid,
this space out here that's

00:02:15.120 --> 00:02:17.890
between the organelles-- and
the organelles, you kind of

00:02:17.890 --> 00:02:22.710
view them as parts of the cell
that do specific things.

00:02:22.710 --> 00:02:24.700
Kind of like organs
do specific things

00:02:24.700 --> 00:02:27.220
within our own bodies.

00:02:27.220 --> 00:02:30.050
So this-- so between all of the
organelles you have this

00:02:30.050 --> 00:02:31.480
fluidic space.

00:02:31.480 --> 00:02:33.090
This is just fluid
of the cell.

00:02:33.090 --> 00:02:34.340
And that's called
the cytoplasm.

00:02:37.820 --> 00:02:41.560
And that's where glycolysis
occurs.

00:02:41.560 --> 00:02:43.440
So glycolysis occurs
in the cytoplasm.

00:02:47.360 --> 00:02:50.610
Now we all know-- in the
overview video-- we know what

00:02:50.610 --> 00:02:52.150
the next step is.

00:02:52.150 --> 00:02:54.990
The Krebs cycle, or the
citric acid cycle.

00:02:54.990 --> 00:02:58.761
And that actually takes place
in the inner membrane, or I

00:02:58.761 --> 00:03:03.340
should say the inner space
of these mitochondria.

00:03:03.340 --> 00:03:04.820
Let me draw it a little
bit bigger.

00:03:04.820 --> 00:03:06.890
Let me draw a mitochondria
here.

00:03:06.890 --> 00:03:08.590
So this is a mitochondria.

00:03:08.590 --> 00:03:10.340
It has an outer membrane.

00:03:10.340 --> 00:03:11.960
It has an inner membrane.

00:03:11.960 --> 00:03:14.950
If I have just one inner
membrane we call it a crista.

00:03:14.950 --> 00:03:17.430
If we have many, we
call them cristae.

00:03:17.430 --> 00:03:19.565
This little convoluted
inner membrane, let

00:03:19.565 --> 00:03:22.410
me give it a label.

00:03:22.410 --> 00:03:25.430
So they are cristae, plural.

00:03:25.430 --> 00:03:27.540
And then it has two
compartments.

00:03:27.540 --> 00:03:29.930
Because it's divided by
these two membranes.

00:03:29.930 --> 00:03:32.880
This compartment right here is
called the outer compartment.

00:03:32.880 --> 00:03:35.340
This whole thing right there,
that's the outer compartment.

00:03:35.340 --> 00:03:39.660
And then this inner compartment
in here, is called

00:03:39.660 --> 00:03:40.910
the matrix.

00:03:45.200 --> 00:03:49.270
Now you have these pyruvates,
they're not quite just ready

00:03:49.270 --> 00:03:53.220
for the Krebs cycle, but I
guess-- well that's a good

00:03:53.220 --> 00:03:55.920
intro into how do you
make them ready

00:03:55.920 --> 00:03:56.590
for the Krebs cycle?

00:03:56.590 --> 00:03:57.430
They actually get oxidized.

00:03:57.430 --> 00:04:00.900
And I'll just focus on one
of these pyruvates.

00:04:00.900 --> 00:04:03.740
We just have to remember that
the pyruvate, that this

00:04:03.740 --> 00:04:06.730
happens twice for every
molecule of glucose.

00:04:06.730 --> 00:04:09.660
So we have this kind
of preparation step

00:04:09.660 --> 00:04:10.870
for the Krebs Cycle.

00:04:10.870 --> 00:04:12.120
We call that pyruvate
oxidation.

00:04:17.000 --> 00:04:19.860
And essentially what it does
is it cleaves one of these

00:04:19.860 --> 00:04:22.320
carbons off of the pyruvate.

00:04:22.320 --> 00:04:25.650
And so you end up with
a 2-carbon compound.

00:04:25.650 --> 00:04:28.000
You don't have just two carbons,
but its backbone of

00:04:28.000 --> 00:04:29.740
carbons is just two carbons.

00:04:29.740 --> 00:04:30.990
Called acetyl-CoA.

00:04:35.040 --> 00:04:37.100
And if these names are
confusing, because what is

00:04:37.100 --> 00:04:38.590
acetyl coenzyme A?

00:04:38.590 --> 00:04:39.380
These are very bizarre.

00:04:39.380 --> 00:04:41.030
You could do a web search on
them But I'm just going to use

00:04:41.030 --> 00:04:43.360
the words right now, because it
will keep things simple and

00:04:43.360 --> 00:04:44.790
we'llget the big picture.

00:04:44.790 --> 00:04:46.240
So it generates acetyl-CoA,
which is

00:04:46.240 --> 00:04:47.500
this 2-carbon compound.

00:04:47.500 --> 00:04:56.500
And it also reduces some
NAD plus to NADH.

00:04:56.500 --> 00:05:00.010
And this process right here is
often given credit-- or the

00:05:00.010 --> 00:05:02.000
Krebs cycle or the citric
acid cycle gets

00:05:02.000 --> 00:05:03.070
credit for this step.

00:05:03.070 --> 00:05:06.470
But it's really a preparation
step for the Krebs cycle.

00:05:06.470 --> 00:05:11.870
Now once you have this 2-carbon
chain, acetyl-Co-A

00:05:11.870 --> 00:05:12.750
right here.

00:05:12.750 --> 00:05:16.200
you are ready to jump into
the Krebs cycle.

00:05:16.200 --> 00:05:18.080
This long talked-about
Krebs cycle.

00:05:18.080 --> 00:05:20.670
And you'll see in a second
why it's called a cycle.

00:05:20.670 --> 00:05:23.970
Acetyl-CoA, and all of this
is catalyzed by enzymes.

00:05:23.970 --> 00:05:26.900
And enzymes are just proteins
that bring together the

00:05:26.900 --> 00:05:29.540
constituent things that need to
react in the right way so

00:05:29.540 --> 00:05:30.970
that they do react.

00:05:30.970 --> 00:05:33.260
So catalyzed by enzymes.

00:05:33.260 --> 00:05:40.280
This acetyl-CoA merges with
some oxaloacetic acid.

00:05:40.280 --> 00:05:41.540
A very fancy word.

00:05:41.540 --> 00:05:43.880
But this is a 4-carbon
molecule.

00:05:48.090 --> 00:05:51.580
These two guys are kind of
reacted together, or merged

00:05:51.580 --> 00:05:53.570
together, depending on how
you want to view it.

00:05:53.570 --> 00:05:55.640
I'll draw it like that.

00:05:55.640 --> 00:05:57.100
It's all catalyzed by enzymes.

00:05:57.100 --> 00:05:58.000
And this is important.

00:05:58.000 --> 00:06:00.210
Some texts will say, is this an
enzyme catalyzed reaction?

00:06:00.210 --> 00:06:00.740
Yes.

00:06:00.740 --> 00:06:02.070
Everything in the Krebs
cycle is an

00:06:02.070 --> 00:06:03.720
enzyme catalyzed reaction.

00:06:03.720 --> 00:06:06.675
And they form citrate,
or citric acid.

00:06:09.630 --> 00:06:11.470
Which is the same stuff
in your lemonade

00:06:11.470 --> 00:06:12.810
or your orange juice.

00:06:12.810 --> 00:06:18.330
And this is a 6-carbon
molecule.

00:06:18.330 --> 00:06:18.990
Which makes sense.

00:06:18.990 --> 00:06:21.160
You have a 2-carbon
and a 4-carbon.

00:06:21.160 --> 00:06:23.520
You get a 6-carbon molecule.

00:06:23.520 --> 00:06:27.000
And then the citric acid
is then oxidized

00:06:27.000 --> 00:06:28.110
over a bunch of steps.

00:06:28.110 --> 00:06:30.450
And this is a huge
simplification here.

00:06:30.450 --> 00:06:33.540
But it's just oxidized over
a bunch of steps.

00:06:33.540 --> 00:06:35.910
Again, the carbons
are cleaved off.

00:06:35.910 --> 00:06:39.430
Both 2-carbons are cleaved
off of it to get back to

00:06:39.430 --> 00:06:41.410
oxaloacetic acid.

00:06:41.410 --> 00:06:43.630
And you might be saying, when
these carbons are cleaved off,

00:06:43.630 --> 00:06:45.620
like when this carbon
is cleaved off,

00:06:45.620 --> 00:06:48.560
what happens to it?

00:06:48.560 --> 00:06:50.000
It becomes CO2.

00:06:50.000 --> 00:06:52.890
It gets put onto some oxygen
and leaves the system.

00:06:52.890 --> 00:06:56.840
So this is where the oxygen or
the carbons, or the carbon

00:06:56.840 --> 00:06:58.260
dioxide actually gets formed.

00:06:58.260 --> 00:07:00.390
And similarly, when these
carbons get cleaved

00:07:00.390 --> 00:07:04.170
off, it forms CO2.

00:07:04.170 --> 00:07:06.720
And actually, for every molecule
of glucose you have

00:07:06.720 --> 00:07:07.980
six carbons.

00:07:07.980 --> 00:07:11.760
When you do this whole process
once, you are generating three

00:07:11.760 --> 00:07:13.505
molecules of carbon dioxide.

00:07:13.505 --> 00:07:14.630
But you're going
to do it twice.

00:07:14.630 --> 00:07:18.000
You're going to have six carbon
dioxides produced.

00:07:18.000 --> 00:07:20.970
Which accounts for all
of the carbons.

00:07:20.970 --> 00:07:24.090
You get rid of three carbons
for every turn of this.

00:07:24.090 --> 00:07:25.360
Well, two for every turn.

00:07:25.360 --> 00:07:28.400
But really, for the steps after
glycolysis you get rid

00:07:28.400 --> 00:07:29.395
of three carbons.

00:07:29.395 --> 00:07:31.490
But you're going to do it for
each of the pyruvates.

00:07:31.490 --> 00:07:34.350
You're going to get rid of all
six carbons, which will have

00:07:34.350 --> 00:07:35.800
to exhale eventually.

00:07:35.800 --> 00:07:37.930
But this cycle, it doesn't
just generate carbons.

00:07:37.930 --> 00:07:43.150
The whole idea is to generate
NADHs and FADH2s and ATPs.

00:07:43.150 --> 00:07:44.430
So we'll write that here.

00:07:44.430 --> 00:07:45.820
And this is a huge
simplification.

00:07:45.820 --> 00:07:47.930
I'll show you the detailed
picture in a second.

00:07:47.930 --> 00:07:51.730
We'll reduce some NAD
plus into NADH.

00:07:56.030 --> 00:07:57.130
We'll do it again.

00:07:57.130 --> 00:07:58.860
And of course, these are
in separate steps.

00:07:58.860 --> 00:08:00.240
There's intermediate
compounds.

00:08:00.240 --> 00:08:03.200
I'll show you those
in a second.

00:08:03.200 --> 00:08:08.130
Another NAD plus molecule
will be reduced to NADH.

00:08:08.130 --> 00:08:11.040
It will produce some ATP.

00:08:13.630 --> 00:08:15.170
Some ADP will turn into ATP.

00:08:18.920 --> 00:08:22.190
Maybe we have some-- and not
maybe, this is what happens--

00:08:22.190 --> 00:08:30.150
some FAD gets-- let me write
it this way-- some FAD gets

00:08:30.150 --> 00:08:32.100
oxidized into FADH2.

00:08:32.100 --> 00:08:34.950
And the whole reason why we even
pay attention to these,

00:08:34.950 --> 00:08:37.850
you might think, hey cellular
respiration is all about ATP.

00:08:37.850 --> 00:08:40.850
Why do we even pay attention
to these NADHs and these

00:08:40.850 --> 00:08:44.910
FADH2s that get produced
as part of the process?

00:08:44.910 --> 00:08:47.430
The reason why we care is that
these are the inputs into the

00:08:47.430 --> 00:08:48.870
electron transport chain.

00:08:48.870 --> 00:08:51.730
These get oxidized, or they lose
their hydrogens in the

00:08:51.730 --> 00:08:54.530
electron transport chain, and
that's where the bulk of the

00:08:54.530 --> 00:08:56.500
ATP is actually produced.

00:08:56.500 --> 00:08:59.910
And then maybe we'll have
another NAD get reduced, or

00:08:59.910 --> 00:09:01.890
gain in hydrogen.

00:09:01.890 --> 00:09:03.780
Reduction is gaining
an electron.

00:09:03.780 --> 00:09:06.760
Or gaining a hydrogen whose
electron you can hog.

00:09:06.760 --> 00:09:08.870
NADH.

00:09:08.870 --> 00:09:12.170
And then we end up back
at oxaloacetic acid.

00:09:12.170 --> 00:09:15.570
And we can perform the whole
citric acid cycle over again.

00:09:15.570 --> 00:09:17.460
So now that we've written it
all out, let's account for

00:09:17.460 --> 00:09:21.180
what we have. So depending on--
let me draw some dividing

00:09:21.180 --> 00:09:22.890
lines so we know what's what.

00:09:22.890 --> 00:09:26.880
So this right here, everything
to the left of that line right

00:09:26.880 --> 00:09:28.130
there is glycolysis.

00:09:30.450 --> 00:09:31.760
We learned that already.

00:09:31.760 --> 00:09:34.520
And then most-- especially
introductory-- textbooks will

00:09:34.520 --> 00:09:38.480
give the Krebs cycle credit for
this pyruvate oxidation,

00:09:38.480 --> 00:09:40.500
but that's really a
preparatory stage.

00:09:40.500 --> 00:09:43.090
The Krebs cycle is really
formally this part where you

00:09:43.090 --> 00:09:45.310
start with acetyl-CoA,
you merge it

00:09:45.310 --> 00:09:47.400
with oxaloacetic acid.

00:09:47.400 --> 00:09:51.190
And then you go and you form
citric acid, which essentially

00:09:51.190 --> 00:09:54.210
gets oxidized and produces all
of these things that will need

00:09:54.210 --> 00:09:57.750
to either directly produce ATP
or will do it indirectly in

00:09:57.750 --> 00:09:59.030
the electron transport chain.

00:09:59.030 --> 00:10:01.790
But let's account for everything
that we have. Let's

00:10:01.790 --> 00:10:03.630
account for everything
that we have so far.

00:10:03.630 --> 00:10:06.490
We already accounted for the
glycolysis right there.

00:10:06.490 --> 00:10:10.110
Two net ATPs, two NADHs.

00:10:10.110 --> 00:10:13.360
Now, in the citric acid cycle,
or in the Krebs cycle, well

00:10:13.360 --> 00:10:14.730
first we have our pyruvate
oxidation.

00:10:14.730 --> 00:10:16.680
That produced one NADH.

00:10:19.830 --> 00:10:22.040
But remember, if we want to say,
what are we producing for

00:10:22.040 --> 00:10:23.600
every glucose?

00:10:23.600 --> 00:10:26.430
This is what we produced for
each of the pyruvates.

00:10:26.430 --> 00:10:29.510
This NADH was from just
this pyruvate.

00:10:29.510 --> 00:10:33.630
But glycolysis produced
two pyruvates.

00:10:33.630 --> 00:10:38.130
So everything after this, we're
going to multiply by two

00:10:38.130 --> 00:10:40.570
for every molecule of glucose.

00:10:40.570 --> 00:10:43.680
So I'll say, for the pyruvate
oxidation times two means that

00:10:43.680 --> 00:10:45.080
we got two NADHs.

00:10:52.060 --> 00:10:55.900
And then when we look at this
side, the formal Krebs cycle,

00:10:55.900 --> 00:10:56.800
what do we get?

00:10:56.800 --> 00:10:58.150
We have, how many NADHs?

00:10:58.150 --> 00:11:02.110
One, two, three NADHs.

00:11:02.110 --> 00:11:07.730
So three NADHs times two,
because we're going to perform

00:11:07.730 --> 00:11:10.520
this cycle for each of the
pyruvates produced from

00:11:10.520 --> 00:11:11.960
glycolysis.

00:11:11.960 --> 00:11:16.170
So that gives us six NADHs.

00:11:16.170 --> 00:11:19.640
We have one ATP per
turn of the cycle.

00:11:19.640 --> 00:11:20.730
That's going to happen twice.

00:11:20.730 --> 00:11:22.410
Once for each pyruvic acid.

00:11:22.410 --> 00:11:24.980
So we get two ATPs.

00:11:24.980 --> 00:11:29.260
And then we have one FADH2.

00:11:29.260 --> 00:11:31.490
But it's good, we're going
to do this cycle twice.

00:11:31.490 --> 00:11:32.390
This is per cycle.

00:11:32.390 --> 00:11:34.020
So times two.

00:11:34.020 --> 00:11:37.430
We have two FADHs.

00:11:37.430 --> 00:11:42.030
Now, sometimes in a lot of books
these two NADHs, or per

00:11:42.030 --> 00:11:45.400
turn of the Krebs cycle, or per
pyruvate this one NADH,

00:11:45.400 --> 00:11:48.030
they'll give credit to the
Krebs cycle for that.

00:11:48.030 --> 00:11:50.170
So sometimes instead of having
this intermediate step,

00:11:50.170 --> 00:11:52.560
they'll just write four
NADHs right here.

00:11:52.560 --> 00:11:53.590
And you'll do it twice.

00:11:53.590 --> 00:11:55.020
Once for each puruvate.

00:11:55.020 --> 00:11:58.390
So they'll say eight NADHs get
produced from the Krebs cycle.

00:11:58.390 --> 00:12:01.120
But the reality is, six from the
Krebs cycle two from the

00:12:01.120 --> 00:12:02.940
preparatory stage.

00:12:02.940 --> 00:12:06.130
Now the interesting thing is we
can account whether we get

00:12:06.130 --> 00:12:10.360
to the 38 ATPs promised by
cellular respiration.

00:12:10.360 --> 00:12:13.170
We've directly already produced,
for every molecule

00:12:13.170 --> 00:12:17.200
of glucose, two ATPs and
then two more ATPs.

00:12:17.200 --> 00:12:19.990
So we have four ATPs.

00:12:19.990 --> 00:12:20.880
Four ATPs.

00:12:20.880 --> 00:12:21.820
How many NADHs do we have?

00:12:21.820 --> 00:12:25.360
2, 4, and then 4 plus 6 10.

00:12:25.360 --> 00:12:29.850
We have 10 NADHs.

00:12:29.850 --> 00:12:31.380
And then we have 2 FADH2s.

00:12:36.470 --> 00:12:37.710
I think in the first
video on cellular

00:12:37.710 --> 00:12:39.070
respiration I said FADH.

00:12:39.070 --> 00:12:42.860
It should be FADH2, just to be
particular about things.

00:12:42.860 --> 00:12:45.690
And these, so you might say,
hey, where are our 38 ATPs?

00:12:45.690 --> 00:12:48.720
We only have four
ATPs right now.

00:12:48.720 --> 00:12:51.600
But these are actually the
inputs in the electron

00:12:51.600 --> 00:12:52.350
transport chain.

00:12:52.350 --> 00:12:55.370
These molecules right here get
oxidized in the electron

00:12:55.370 --> 00:12:56.460
transport chain.

00:12:56.460 --> 00:12:59.460
Every NADH in the electron
transport chain

00:12:59.460 --> 00:13:01.900
produces three ATPs.

00:13:01.900 --> 00:13:08.120
So these 10 NADHs are going
to produce 30 ATPs in the

00:13:08.120 --> 00:13:10.530
electron transport chain.

00:13:10.530 --> 00:13:14.810
And each FADH2, when it gets
oxidized and gets turned back

00:13:14.810 --> 00:13:18.170
into FAD in the electron
transport chain,

00:13:18.170 --> 00:13:19.610
will produce two ATPs.

00:13:19.610 --> 00:13:25.050
So two of them are going to
produce four ATPs in the

00:13:25.050 --> 00:13:27.320
electron transport chain.

00:13:27.320 --> 00:13:29.140
So we now see, we get
four from just what

00:13:29.140 --> 00:13:29.960
we've done so far.

00:13:29.960 --> 00:13:33.200
Glycolysis, the preparatory
stage and the Krebs or citric

00:13:33.200 --> 00:13:34.220
acid cycle.

00:13:34.220 --> 00:13:37.330
And then eventually, these
outputs from glycolysis and

00:13:37.330 --> 00:13:39.930
the citric acid cycle, when
they get into the electron

00:13:39.930 --> 00:13:42.690
transport chain, are going
to produce another 34.

00:13:42.690 --> 00:13:48.380
So 34 plus 4, it does get us
to the promised 38 ATP that

00:13:48.380 --> 00:13:51.840
you would expect in a
super-efficient cell.

00:13:51.840 --> 00:13:53.630
This is kind of your theoretical
maximum.

00:13:53.630 --> 00:13:55.830
In most cells they really
don't get quite there.

00:13:55.830 --> 00:13:58.120
But this is a good number to
know if you're going to take

00:13:58.120 --> 00:14:01.680
the AP bio test or in most
introductory biology courses.

00:14:01.680 --> 00:14:03.570
There's one other point
I want to make here.

00:14:03.570 --> 00:14:06.790
Everything we've talked about
so far, this is carbohydrate

00:14:06.790 --> 00:14:07.370
metabolism.

00:14:07.370 --> 00:14:09.300
Or sugar catabolism,
we could call it.

00:14:09.300 --> 00:14:11.850
We're breaking down sugars
to produce ATP.

00:14:11.850 --> 00:14:13.780
Glucose was our starting
point.

00:14:13.780 --> 00:14:18.030
But animals, including us, we
can catabolize other things.

00:14:18.030 --> 00:14:20.870
We can catabolize proteins.

00:14:20.870 --> 00:14:26.230
We can catabolize fats.

00:14:26.230 --> 00:14:29.090
If you have any fat on your
body, you have energy.

00:14:29.090 --> 00:14:31.300
In theory, your body should be
able to take that fat and you

00:14:31.300 --> 00:14:32.730
should be able to do
things with that.

00:14:32.730 --> 00:14:34.750
You should be able
to generate ATP.

00:14:34.750 --> 00:14:37.250
And the interesting thing, the
reason why I bring it up here,

00:14:37.250 --> 00:14:39.880
is obviously glycolysis is of
no use to these things.

00:14:39.880 --> 00:14:44.200
Although fats can be turned
into glucose in the liver.

00:14:44.200 --> 00:14:47.210
But the interesting thing is
that the Krebs cycle is the

00:14:47.210 --> 00:14:51.000
entry point for these other
catabolic mechanisms. Proteins

00:14:51.000 --> 00:14:53.900
can be broken down into amino
acids, which can be broken

00:14:53.900 --> 00:14:55.430
down into acetyl-CoA.

00:14:55.430 --> 00:14:58.550
Fats can be turned into glucose,
which actually could

00:14:58.550 --> 00:15:01.070
then go the whole cellular
respiration.

00:15:01.070 --> 00:15:05.020
But the big picture here is
acetyl-CoA is the general

00:15:05.020 --> 00:15:09.300
catabolic intermediary that can
then enter the Krebs cycle

00:15:09.300 --> 00:15:12.200
and generate ATP regardless
of whether our fuel is

00:15:12.200 --> 00:15:16.890
carbohydrates, sugars,
proteins or fats.

00:15:16.890 --> 00:15:20.750
Now, we have a good sense of how
everything works out right

00:15:20.750 --> 00:15:22.210
now, I think.

00:15:22.210 --> 00:15:24.890
Now I'm going to show you a
diagram that you might see in

00:15:24.890 --> 00:15:26.700
your biology textbook.

00:15:26.700 --> 00:15:30.250
Or I'll actually show you the
actual diagram from Wikipedia.

00:15:30.250 --> 00:15:31.650
I just want to show you,
this looks very

00:15:31.650 --> 00:15:32.940
daunting and very confusing.

00:15:32.940 --> 00:15:36.570
And I think that's why many of
us have trouble with cellular

00:15:36.570 --> 00:15:37.670
respiration initially.

00:15:37.670 --> 00:15:39.720
Because there's just so
much information.

00:15:39.720 --> 00:15:41.660
It's hard to process
what's important.

00:15:41.660 --> 00:15:43.640
But I want to just highlight
the important steps here.

00:15:43.640 --> 00:15:46.200
Just so you see it's the same
thing that we talked about.

00:15:46.200 --> 00:15:49.070
From glycolysis you produce
two pyruvates.

00:15:49.070 --> 00:15:50.300
That's the pyruvate
right there.

00:15:50.300 --> 00:15:52.040
They actually show its
molecular structure.

00:15:52.040 --> 00:15:54.880
This is the pyruvate oxidation
step that I talked about.

00:15:54.880 --> 00:15:56.570
The preparatory step.

00:15:56.570 --> 00:15:58.670
And you see we produce
a carbon dioxide.

00:15:58.670 --> 00:16:03.520
And we reduce NAD
plus into NADH.

00:16:03.520 --> 00:16:06.910
Then we're ready to enter
the Krebs cycle.

00:16:06.910 --> 00:16:11.230
The acetyl-CoA and the
oxaloacetate or oxaloacetic

00:16:11.230 --> 00:16:14.490
acid, they are reacted
together to

00:16:14.490 --> 00:16:15.860
create citric acid.

00:16:15.860 --> 00:16:18.180
They've actually drawn
the molecule there.

00:16:18.180 --> 00:16:21.110
And then the citric acid is
oxidized through the Krebs

00:16:21.110 --> 00:16:22.260
cycle right there.

00:16:22.260 --> 00:16:24.220
All of these steps, each
of these steps are

00:16:24.220 --> 00:16:25.590
facilitated by enzymes.

00:16:25.590 --> 00:16:27.100
And it gets oxidized.

00:16:27.100 --> 00:16:29.900
But I want to highlight
the interesting parts.

00:16:29.900 --> 00:16:33.960
Here we have an NAD get
reduced to NADH.

00:16:33.960 --> 00:16:36.950
We have another NAD get
reduced to NADH.

00:16:36.950 --> 00:16:39.960
And then over here, another
NAD gets reduced to NADH.

00:16:39.960 --> 00:16:43.750
So, so far, if you include the
preparatory step, we've had

00:16:43.750 --> 00:16:47.550
four NADHs formed, three
directly from the Krebs cycle.

00:16:47.550 --> 00:16:49.120
That's just what I told you.

00:16:49.120 --> 00:16:52.220
Now we have, in this diagram
they say GDP.

00:16:52.220 --> 00:16:55.310
GTP gets formed from GDP.

00:16:55.310 --> 00:16:57.760
The GTP is just guanosine
triphosphate.

00:16:57.760 --> 00:17:01.130
It's another purine that can
be a source of energy.

00:17:01.130 --> 00:17:03.570
But then that later can be
used to form an ATP.

00:17:03.570 --> 00:17:05.530
So this is just the way they
happen to draw it.

00:17:05.530 --> 00:17:07.680
But this is the actual ATP
that I drew in the

00:17:07.680 --> 00:17:09.069
diagram on the top.

00:17:09.069 --> 00:17:10.210
And then they have
this Q group.

00:17:10.210 --> 00:17:11.210
And I won't go into it.

00:17:11.210 --> 00:17:14.260
And then it gets reduced
over here.

00:17:14.260 --> 00:17:15.660
It gets those two hydrogens.

00:17:15.660 --> 00:17:19.400
But that essentially ends
up reducing the FADH2s.

00:17:19.400 --> 00:17:24.270
So this is where the FADH2
gets produced.

00:17:24.270 --> 00:17:28.119
So as promised, we produced,
for each pyruvate that

00:17:28.119 --> 00:17:30.280
inputted-- remember, so we're
going to do it twice-- for

00:17:30.280 --> 00:17:35.990
each pyruvate we produced one,
two, three, four NADHs.

00:17:35.990 --> 00:17:40.550
We produced one ATP
and one FADH2.

00:17:40.550 --> 00:17:45.050
That's exactly what
we saw up here.

00:17:45.050 --> 00:17:47.000
I'll see you in the
next video.


Overview of glycolysis

WEBVTT
Kind: captions
Language: en

00:00:00.490 --> 00:00:03.220
We've already learned that
cellular respiration can be

00:00:03.220 --> 00:00:05.820
broken down into roughly
three phases.

00:00:11.490 --> 00:00:16.760
The first is glycolysis, which
literally means the breaking

00:00:16.760 --> 00:00:18.010
down of glucose.

00:00:23.620 --> 00:00:27.540
And then this can occur with
or without oxygen.

00:00:27.540 --> 00:00:31.590
If we don't have oxygen, then
we go over to fermentation.

00:00:31.590 --> 00:00:34.800
We'll talk about that
in the future.

00:00:34.800 --> 00:00:37.320
Go over to fermentation
and in humans it

00:00:37.320 --> 00:00:38.750
produces lactic acid.

00:00:38.750 --> 00:00:41.150
In other types of organisms
it might

00:00:41.150 --> 00:00:43.200
produce alcohol or ethanol.

00:00:43.200 --> 00:00:45.675
But if we have oxygen-- and for
the most part we're going

00:00:45.675 --> 00:00:48.690
to assume that we can proceed
forward with oxygen-- if there

00:00:48.690 --> 00:00:50.610
is oxygen, then we could
proceed forward

00:00:50.610 --> 00:00:54.190
to the Krebs cycle.

00:00:54.190 --> 00:00:58.750
Sometimes called the citric acid
cycle because it deals

00:00:58.750 --> 00:01:00.390
with citric acid.

00:01:00.390 --> 00:01:03.390
The same thing that's in
orange juice or lemons.

00:01:03.390 --> 00:01:05.630
And then from there
we proceed to the

00:01:05.630 --> 00:01:07.310
electron transport chain.

00:01:10.090 --> 00:01:12.750
And we learned in the first
overview video of cellular

00:01:12.750 --> 00:01:15.610
respiration that this is where
the bulk of the ATP is

00:01:15.610 --> 00:01:16.500
actually produced.

00:01:16.500 --> 00:01:18.920
Although it uses raw materials
that came out of

00:01:18.920 --> 00:01:20.360
these phases up here.

00:01:20.360 --> 00:01:23.460
Now what I want to do in this
video is just focus on

00:01:23.460 --> 00:01:24.710
glycolysis.

00:01:27.500 --> 00:01:31.080
And this is kind of-- it's
sometimes a challenging task

00:01:31.080 --> 00:01:32.830
because you can really get
stuck in the weeds.

00:01:32.830 --> 00:01:34.550
And I'll show you the weeds
in a little bit,

00:01:34.550 --> 00:01:35.480
and the actual mechanism.

00:01:35.480 --> 00:01:36.750
And it can be very daunting.

00:01:36.750 --> 00:01:39.160
But what I want to do is
simplify it for you so you can

00:01:39.160 --> 00:01:40.420
have the big take-aways.

00:01:40.420 --> 00:01:42.550
And then we can appreciate, and
then maybe when we look at

00:01:42.550 --> 00:01:45.770
the weeds of glycolysis we
can make a little bit

00:01:45.770 --> 00:01:46.940
more sense of it.

00:01:46.940 --> 00:01:49.230
So glycolysis, or really
cellular respiration, it

00:01:49.230 --> 00:01:50.480
starts off with glucose.

00:01:53.230 --> 00:01:55.130
And glucose, we know
its formula.

00:01:55.130 --> 00:01:59.660
It's C6H12O6.

00:01:59.660 --> 00:02:01.850
And I could draw its whole
structure; it would take a

00:02:01.850 --> 00:02:02.300
little time.

00:02:02.300 --> 00:02:04.270
But I'm just going to focus
on the carbon backbone.

00:02:04.270 --> 00:02:07.010
So it is a ring, or
can be a ring.

00:02:07.010 --> 00:02:12.700
But I'm just going to draw it
as six carbons in a row.

00:02:12.700 --> 00:02:15.950
Now there's two kind of
important phases of glycolysis

00:02:15.950 --> 00:02:16.820
that are good to know.

00:02:16.820 --> 00:02:19.420
One, I call the investment
phase.

00:02:19.420 --> 00:02:23.000
And the investment phase
actually uses two ATPs.

00:02:29.910 --> 00:02:32.270
So you know, the whole purpose
of cellular respiration is to

00:02:32.270 --> 00:02:35.650
generate ATPs, but right from
the get-go I actually have to

00:02:35.650 --> 00:02:37.360
use two ATPs.

00:02:37.360 --> 00:02:40.980
But I use two ATPs and then I'm
essentially going to break

00:02:40.980 --> 00:02:50.710
up the glucose into two 3-carbon
compounds right here

00:02:50.710 --> 00:02:53.730
that actually also have a
phosphate group on them.

00:02:53.730 --> 00:02:56.690
The phosphate groups are
coming from those ATPs.

00:02:56.690 --> 00:02:58.910
They also have a phosphate
group on them and this is

00:02:58.910 --> 00:03:01.520
often called-- well, there's
a lot of names for it.

00:03:01.520 --> 00:03:02.910
Sometimes it's called PGAL.

00:03:02.910 --> 00:03:04.040
You really don't have
to know this.

00:03:04.040 --> 00:03:12.360
Or phosphoglyceraldehyde, really
challenging my spelling

00:03:12.360 --> 00:03:13.420
skills right here.

00:03:13.420 --> 00:03:14.420
That's not that important
to know.

00:03:14.420 --> 00:03:15.950
All you have to know
is in this first

00:03:15.950 --> 00:03:17.840
phase you use two ATPs.

00:03:17.840 --> 00:03:20.350
That's why I call it the
investment phase.

00:03:20.350 --> 00:03:29.020
If we use a business analogy,
investment phase.

00:03:29.020 --> 00:03:33.510
And then each of these two PGAL
molecules can then go

00:03:33.510 --> 00:03:35.350
into the payoff phase.

00:03:35.350 --> 00:03:39.480
So in the payoff phase,
each of these

00:03:39.480 --> 00:03:42.280
PGALs turn into pyruvate.

00:03:42.280 --> 00:03:45.310
Which is another 3-carbon,
but it's reconfigured.

00:03:45.310 --> 00:03:48.670
But the process of it going to
pyruvate-- and let me write

00:03:48.670 --> 00:03:53.130
pyruvate in blue, because this
is something that, at least

00:03:53.130 --> 00:03:54.620
it's good to know the word.

00:03:54.620 --> 00:03:56.290
And I'll show you the structure
in a second.

00:03:56.290 --> 00:03:57.100
Pyruvate.

00:03:57.100 --> 00:03:59.730
Sometimes it's called
pyruvic acid.

00:03:59.730 --> 00:04:02.560
Same thing.

00:04:02.560 --> 00:04:05.890
And that's essentially the end
product of glycolysis.

00:04:05.890 --> 00:04:08.200
So you start off with glucose
in the investment phase.

00:04:08.200 --> 00:04:10.480
You end up in this
phosphoglyceraldehyde, which

00:04:10.480 --> 00:04:12.540
essentially you broke up your
glucose and you put a

00:04:12.540 --> 00:04:14.070
phosphate on either end of it.

00:04:14.070 --> 00:04:17.310
And then those each
independently go through the

00:04:17.310 --> 00:04:18.490
payoff phase.

00:04:18.490 --> 00:04:22.029
So you end up with two molecules
of pyruvate for

00:04:22.029 --> 00:04:25.220
every molecule of glucose
you started off with.

00:04:25.220 --> 00:04:27.860
Now you're saying, hey, Sal,
there was a payoff phase, what

00:04:27.860 --> 00:04:30.310
was our payoff?

00:04:30.310 --> 00:04:35.710
Well our payoff, we got, for
each-- let me write this down

00:04:35.710 --> 00:04:37.280
as a payoff phase.

00:04:37.280 --> 00:04:38.530
This is our payoff phase.

00:04:41.460 --> 00:04:43.150
And I apologize for the
white background.

00:04:43.150 --> 00:04:45.300
I did it because, the mechanism
I'm showing you, I

00:04:45.300 --> 00:04:47.800
copy-and-pasted it from
Wikipedia, and they had a

00:04:47.800 --> 00:04:50.390
white background so I just ran
with the white background for

00:04:50.390 --> 00:04:50.950
this video.

00:04:50.950 --> 00:04:53.910
But I, personally at least, like
the black background a

00:04:53.910 --> 00:04:55.040
lot better.

00:04:55.040 --> 00:04:57.750
But this is the payoff
phase right here.

00:04:57.750 --> 00:05:00.990
And so when we go from the
phosphoglyceraldehyde to the

00:05:00.990 --> 00:05:05.080
pyruvate or the pyruvic acid,
we produce two things.

00:05:05.080 --> 00:05:07.420
Or I guess we could say we
produce three things.

00:05:07.420 --> 00:05:11.860
We produce, each of
these PGALs to

00:05:11.860 --> 00:05:13.450
pyruvates produce two ATPs.

00:05:16.120 --> 00:05:17.880
So I'm going to produce two
ATPs there, I'm going to

00:05:17.880 --> 00:05:20.490
produce two ATPs there.

00:05:20.490 --> 00:05:22.410
And then they each
produce an NADH.

00:05:27.540 --> 00:05:29.820
And I'll do it in
a darker color.

00:05:29.820 --> 00:05:31.070
NADH.

00:05:36.940 --> 00:05:39.910
And of course they're not
producing the whole molecule

00:05:39.910 --> 00:05:40.800
in a vacuum.

00:05:40.800 --> 00:05:43.450
Essentially what they're doing
is they're starting with the

00:05:43.450 --> 00:05:47.640
raw material of an NAD plus-- so
they start off with an NAD

00:05:47.640 --> 00:05:51.260
plus-- and they essentially
reduce

00:05:51.260 --> 00:05:53.150
it by adding a hydrogen.

00:05:53.150 --> 00:05:55.170
Remember, we learned a couple
of videos ago that you could

00:05:55.170 --> 00:05:57.830
view reduction as a
gain in hydrogen.

00:05:57.830 --> 00:06:01.110
So the NAD gets reduced
to NADH.

00:06:01.110 --> 00:06:05.110
And then later on, these NADHs
are used in electron transport

00:06:05.110 --> 00:06:08.470
chain to actually
produce ATPs.

00:06:08.470 --> 00:06:13.090
So the big take-away here, if
I were to write the reaction

00:06:13.090 --> 00:06:16.390
that we get for glycolysis,
is that you

00:06:16.390 --> 00:06:17.640
start off with a glucose.

00:06:21.480 --> 00:06:24.520
And you need some NAD plus.

00:06:27.840 --> 00:06:29.870
And actually, for every mole
of glucose, you're going to

00:06:29.870 --> 00:06:33.540
need two NAD plusses.

00:06:33.540 --> 00:06:34.990
You're going to need two ATPs.

00:06:38.420 --> 00:06:40.860
So I'm just writing all the
ingredients that we need to

00:06:40.860 --> 00:06:42.350
start off with.

00:06:42.350 --> 00:06:44.750
And then you're going to need--
well, let me say, these

00:06:44.750 --> 00:06:47.290
guys are going to be ADPs before
we turn them to ATPs.

00:06:47.290 --> 00:06:51.550
So I'll write plus four ADPs.

00:06:51.550 --> 00:06:57.150
And then, after performing
glycolysis-- and

00:06:57.150 --> 00:06:57.840
let me write it here.

00:06:57.840 --> 00:07:01.055
Let me write also-- sorry
that was ADPs.

00:07:04.950 --> 00:07:08.970
Let me just rewrite that
part right there.

00:07:08.970 --> 00:07:10.540
Four ADPs.

00:07:10.540 --> 00:07:12.390
And then you maybe need
two phosphate groups.

00:07:12.390 --> 00:07:15.820
Because we're going to need
four phosphate groups.

00:07:15.820 --> 00:07:18.540
Plus four-- I'll just call
them, sometimes they're

00:07:18.540 --> 00:07:19.310
written like that.

00:07:19.310 --> 00:07:20.440
But maybe I'll write
it like this.

00:07:20.440 --> 00:07:21.740
Four phosphate groups.

00:07:25.670 --> 00:07:30.790
And then once you perform
glycolysis, you have two

00:07:30.790 --> 00:07:37.680
pyruvates, you have two NADHs.

00:07:40.660 --> 00:07:43.190
The NAD has been reduced.

00:07:43.190 --> 00:07:45.010
It gained a hydrogen.

00:07:45.010 --> 00:07:45.850
RIG.

00:07:45.850 --> 00:07:46.590
OIL RIG.

00:07:46.590 --> 00:07:48.850
Reduction is gain an electron.

00:07:48.850 --> 00:07:50.200
But in the biological
sense, we think of

00:07:50.200 --> 00:07:51.110
it gaining the hydrogen.

00:07:51.110 --> 00:07:53.320
Because hydrogen is very
non-electronegative, so you're

00:07:53.320 --> 00:07:54.260
hogging its electrons.

00:07:54.260 --> 00:07:56.020
You've gained its electrons.

00:07:56.020 --> 00:08:01.810
So two NADHs and then plus these
two ATPs get used in the

00:08:01.810 --> 00:08:02.720
investment phase.

00:08:02.720 --> 00:08:04.390
That's why I kind of wrote
them a little separately.

00:08:04.390 --> 00:08:05.860
So these two get used.

00:08:05.860 --> 00:08:07.865
So then you're left
with two ADPs.

00:08:10.860 --> 00:08:13.630
And then these guys,
essentially,

00:08:13.630 --> 00:08:14.750
get turned into ATPs.

00:08:14.750 --> 00:08:19.090
So plus four ATPs.

00:08:19.090 --> 00:08:20.570
I guess we didn't need four.

00:08:20.570 --> 00:08:22.890
We only needed a net of
two phosphate groups.

00:08:22.890 --> 00:08:24.570
Because two jump off of here.

00:08:24.570 --> 00:08:26.710
And then we need a total
of two more to get

00:08:26.710 --> 00:08:28.560
four jumping on there.

00:08:28.560 --> 00:08:31.270
But the big picture is, you
start with a glucose, you end

00:08:31.270 --> 00:08:33.020
up with two pyruvates.

00:08:33.020 --> 00:08:35.090
You use up two ATPs.

00:08:35.090 --> 00:08:36.909
You get four ATPs.

00:08:36.909 --> 00:08:39.559
So you have a net of
two ATPs formed.

00:08:39.559 --> 00:08:41.490
Let me write that very big.

00:08:41.490 --> 00:08:45.840
Net, what you get out of
glycolysis, is two ATPs.

00:08:45.840 --> 00:08:51.290
You get two NADHs that can
each later be used in the

00:08:51.290 --> 00:08:54.600
electron transport chain
to produce three ATPs.

00:08:54.600 --> 00:08:59.150
You get two NADHs and you get
two pyruvates, which are going

00:08:59.150 --> 00:09:02.930
to be re-engineered into
acetyl-CoAs that are going to

00:09:02.930 --> 00:09:04.950
be the raw materials for
the Krebs cycle.

00:09:04.950 --> 00:09:10.690
But these are the outputs
of glycolysis.

00:09:10.690 --> 00:09:13.070
So now that we have that big
picture, let's actually look

00:09:13.070 --> 00:09:13.800
at the mechanism.

00:09:13.800 --> 00:09:15.730
Because this is a little
bit more daunting

00:09:15.730 --> 00:09:16.440
when you see it here.

00:09:16.440 --> 00:09:18.970
But we'll see the same themes
that I just talked about.

00:09:18.970 --> 00:09:22.000
We're starting with a
glucose right there.

00:09:22.000 --> 00:09:24.270
It is a six chain.

00:09:24.270 --> 00:09:26.060
It's in a circle, in a ring.

00:09:26.060 --> 00:09:30.280
One, two, three, four,
five, six carbons.

00:09:30.280 --> 00:09:33.110
I could write it like that,
just to make a huge

00:09:33.110 --> 00:09:34.226
oversimplification.

00:09:34.226 --> 00:09:36.020
It goes through a few steps.

00:09:36.020 --> 00:09:37.460
I use an ATP here.

00:09:37.460 --> 00:09:39.430
So let me do that in a color.

00:09:39.430 --> 00:09:42.310
Let me do it in orange whenever
I use an ATP.

00:09:42.310 --> 00:09:43.870
I use one ATP there.

00:09:43.870 --> 00:09:46.050
I use one ATP there.

00:09:46.050 --> 00:09:48.500
And just like I told you,
they have a slightly

00:09:48.500 --> 00:09:49.370
different name for it.

00:09:49.370 --> 00:09:49.880
But this is the

00:09:49.880 --> 00:09:52.040
phosphoglyceraldehyde right here.

00:09:52.040 --> 00:09:54.480
They call it glyceraldehyde
3-phosphate.

00:09:54.480 --> 00:09:56.850
It's the exact same molecule.

00:09:56.850 --> 00:10:00.130
But as you can see, just when I
drew it very roughly before,

00:10:00.130 --> 00:10:03.020
you've got one, two three
carbons there.

00:10:05.670 --> 00:10:07.630
And it also has a phosphate
group on it.

00:10:07.630 --> 00:10:09.600
The phosphate group's actually
attached to the oxygen.

00:10:09.600 --> 00:10:12.160
But for just for simplification
I draw the

00:10:12.160 --> 00:10:13.560
phosphate group just
like that.

00:10:13.560 --> 00:10:15.750
And I showed that right here.

00:10:15.750 --> 00:10:16.440
This was the

00:10:16.440 --> 00:10:18.535
phosphoglyceraldehyde right here.

00:10:18.535 --> 00:10:20.700
This is the actual structure
up here.

00:10:20.700 --> 00:10:23.630
But I think sometimes when you
look at the structure it's

00:10:23.630 --> 00:10:24.680
easy to miss the big picture.

00:10:24.680 --> 00:10:25.480
And there are two of these.

00:10:25.480 --> 00:10:28.600
They kind of say that you can
go back and forth with this,

00:10:28.600 --> 00:10:31.190
with this other kind
of isomer of this.

00:10:31.190 --> 00:10:32.740
But the important thing is that
you have two of these

00:10:32.740 --> 00:10:34.950
compounds that are now
3-carbon compounds.

00:10:34.950 --> 00:10:36.520
Glucose has been split.

00:10:36.520 --> 00:10:39.650
And now we're ready to enter
the payoff phase.

00:10:39.650 --> 00:10:43.050
Remember you have two of these
compounds right here.

00:10:43.050 --> 00:10:44.610
That's why, when they drew this
mechanism, they wrote

00:10:44.610 --> 00:10:46.310
times two right there.

00:10:46.310 --> 00:10:47.650
Because the glucose has
been split into

00:10:47.650 --> 00:10:49.090
two of these molecules.

00:10:49.090 --> 00:10:50.810
So each of the molecules
are now going to

00:10:50.810 --> 00:10:52.000
do this right here.

00:10:52.000 --> 00:10:55.430
And for each of the
glyceraldehyde 3-phosphates,

00:10:55.430 --> 00:10:58.600
or PGALs, or
phosphoglyceraldehyde, we can

00:10:58.600 --> 00:11:02.920
look at the mechanism and say,
OK look here, there's going to

00:11:02.920 --> 00:11:06.270
be an ADP turning into
an ATP there.

00:11:06.270 --> 00:11:09.090
So this is plus one ATP.

00:11:09.090 --> 00:11:12.410
And then we see it again
happening here

00:11:12.410 --> 00:11:14.710
on our way to pyruvate.

00:11:14.710 --> 00:11:17.100
On our way to pyruvate right,
there then we have another

00:11:17.100 --> 00:11:20.330
plus one ATP.

00:11:20.330 --> 00:11:23.640
So for each of the PGALs, or
the phosphoglyceraldehydes

00:11:23.640 --> 00:11:29.290
that were produced, we're
producing two ATPs in the

00:11:29.290 --> 00:11:30.200
payoff phase.

00:11:30.200 --> 00:11:31.410
Now there were two of these.

00:11:31.410 --> 00:11:35.040
So total for one glucose, we're
going to produce four

00:11:35.040 --> 00:11:37.340
ATPs in the payoff phase.

00:11:37.340 --> 00:11:39.420
So in the payoff phase,
four ATPs.

00:11:39.420 --> 00:11:43.230
In the investment phase
we used one, two ATPs.

00:11:43.230 --> 00:11:46.080
So total net ATPs directly
generated from

00:11:46.080 --> 00:11:49.070
glycolysis is two ATPs.

00:11:49.070 --> 00:11:51.440
Four, gross produced.

00:11:51.440 --> 00:11:54.100
But we had to invest two in
the investment phase.

00:11:54.100 --> 00:11:58.090
And then the NADs and the NADHs,
we see right here.

00:11:58.090 --> 00:12:00.760
For each phosphoglyceraldehyde,
or

00:12:00.760 --> 00:12:03.700
glyceraldehyde 3-phosphates or
PGALs or whatever you want to

00:12:03.700 --> 00:12:07.540
call them, at this stage right
here you see that we are

00:12:07.540 --> 00:12:11.800
reducing NAD plus to NADH.

00:12:11.800 --> 00:12:14.935
So this happens once for each
of these compounds.

00:12:14.935 --> 00:12:16.500
And obviously there
are two of these.

00:12:16.500 --> 00:12:18.330
Glucose got split into
two of these guys.

00:12:18.330 --> 00:12:22.900
So two NADHs are going
to be produced.

00:12:22.900 --> 00:12:25.080
And later these are going to
be used in the electron

00:12:25.080 --> 00:12:30.900
transport chain to actually
each produce three ATPs.

00:12:30.900 --> 00:12:32.870
And then finally, when
everything is said and done,

00:12:32.870 --> 00:12:34.250
we're left with the pyruvates.

00:12:34.250 --> 00:12:36.715
And it's nice, at least that
they made it nice and big.

00:12:36.715 --> 00:12:39.550
We can take a look at what
a pyruvate looks like.

00:12:39.550 --> 00:12:42.600
And just as promised, we can
look at all the oxygen bonds

00:12:42.600 --> 00:12:43.140
and all that.

00:12:43.140 --> 00:12:45.635
But it's a 3-carbon structure.

00:12:45.635 --> 00:12:47.780
It has a 3-carbon backbone.

00:12:47.780 --> 00:12:51.340
So the end result is that the
carbon, that the glucose got

00:12:51.340 --> 00:12:52.280
split in half.

00:12:52.280 --> 00:12:53.220
It got oxidized.

00:12:53.220 --> 00:12:54.960
Some of the hydrogens got
stripped off of it.

00:12:54.960 --> 00:12:57.190
As you can see there's only
three hydrogens here.

00:12:57.190 --> 00:12:59.810
We started off with 12
hydrogens in glucose.

00:12:59.810 --> 00:13:03.750
And now it has its carbons
bonding more

00:13:03.750 --> 00:13:04.830
strongly with oxygen.

00:13:04.830 --> 00:13:07.110
So it's essentially having its
electrons stolen by the

00:13:07.110 --> 00:13:09.160
oxygens, or hogged
by the oxygens.

00:13:09.160 --> 00:13:11.430
So carbon has gotten oxidized
in this process.

00:13:11.430 --> 00:13:14.130
There's going to be more
oxidation left to do.

00:13:14.130 --> 00:13:20.470
And in the process we were able
to generate two net ATPs

00:13:20.470 --> 00:13:26.930
and two NADHs that can later
be used to produce ATPs.

00:13:26.930 --> 00:13:29.570
Anyway, hopefully you
found that helpful.


Oxidation and reduction in cellular respiration

WEBVTT
Kind: captions
Language: en

00:00:00.590 --> 00:00:03.390
Now that we have a little bit
of a review of oxidation and

00:00:03.390 --> 00:00:05.840
reduction under our belts, let's
see if we can apply what

00:00:05.840 --> 00:00:10.330
we now, maybe, re-understand
to cellular respiration.

00:00:10.330 --> 00:00:14.650
So cellular respiration, for
every mole of a glucose,

00:00:14.650 --> 00:00:19.960
C6H12O6, we combine that--
and maybe that's

00:00:19.960 --> 00:00:21.040
in an aqueous state.

00:00:21.040 --> 00:00:22.560
It's dissolved in water.

00:00:22.560 --> 00:00:28.110
We combine that with six moles
of molecular oxygen.

00:00:28.110 --> 00:00:31.990
And then our cells perform
cellular respiration in a

00:00:31.990 --> 00:00:33.150
whole series of steps.

00:00:33.150 --> 00:00:34.550
And I'll do more
videos on that.

00:00:39.470 --> 00:00:40.780
I'll just abbreviate it.

00:00:40.780 --> 00:00:47.520
And then we end up with six
moles of carbon dioxide.

00:00:47.520 --> 00:00:50.720
We have to breathe this oxygen
in order to perform cellular

00:00:50.720 --> 00:00:53.650
respiration and we have to
breathe this carbon dioxide

00:00:53.650 --> 00:00:55.710
out because it's just a
byproduct of cellular

00:00:55.710 --> 00:00:56.630
respiration.

00:00:56.630 --> 00:01:00.900
Six moles of carbon dioxide,
six moles of water.

00:01:00.900 --> 00:01:05.450
And the whole point of cellular
respiration is, plus

00:01:05.450 --> 00:01:09.400
some energy is generated
by this reaction.

00:01:09.400 --> 00:01:11.630
And our bodies store
this energy.

00:01:11.630 --> 00:01:13.890
Well, some of it is just
turned into heat.

00:01:13.890 --> 00:01:16.150
But the whole point of cellular
respiration is to

00:01:16.150 --> 00:01:20.650
store it as 38 ATPs, which we've
learned already is the

00:01:20.650 --> 00:01:23.160
energy currency of biological
systems.

00:01:23.160 --> 00:01:26.080
And then our bodies, or
biological systems in general,

00:01:26.080 --> 00:01:30.350
can use these ATPs to contract
muscles or generate nerve

00:01:30.350 --> 00:01:33.500
impulses or grow cells or divide
cells or whatever else

00:01:33.500 --> 00:01:36.300
that a biological system
has to do.

00:01:36.300 --> 00:01:38.790
In the last video we learned a
little bit about oxidation and

00:01:38.790 --> 00:01:42.060
reduction, so let's apply
those ideas here.

00:01:42.060 --> 00:01:47.510
Now we saw in the last video
that a chemist would say-- let

00:01:47.510 --> 00:01:49.810
me write it this way-- a
chemist would say that

00:01:49.810 --> 00:01:55.510
oxidation means losing
electrons, or not being able

00:01:55.510 --> 00:01:56.760
to hog them.

00:01:59.150 --> 00:02:01.160
While a chemist will
tell you that

00:02:01.160 --> 00:02:06.310
reduction is gaining electrons.

00:02:12.020 --> 00:02:15.460
And if you have trouble
remembering, oxidation is

00:02:15.460 --> 00:02:19.680
losing, that's kind of OIL,
that's the mnemonic.

00:02:19.680 --> 00:02:21.240
Oxygen is losing electrons.

00:02:21.240 --> 00:02:22.490
Reduction is gaining.

00:02:22.490 --> 00:02:24.060
Or, RIG.

00:02:24.060 --> 00:02:25.060
So OIL RIG.

00:02:25.060 --> 00:02:26.760
This is what you learned
in chemistry class.

00:02:26.760 --> 00:02:30.900
Now biologists or biochemists
will say, oh, well, you know I

00:02:30.900 --> 00:02:33.220
like to define it a little
bit differently.

00:02:33.220 --> 00:02:40.540
A biologist will say that
oxidation is losing hydrogen

00:02:40.540 --> 00:02:52.660
atoms. And they'll say reduction
is gaining hydrogen

00:02:52.660 --> 00:02:55.730
atoms. And we saw in the last
video that this definition is

00:02:55.730 --> 00:02:57.940
actually hard when you're
applying it to hydrogen

00:02:57.940 --> 00:03:00.150
because it's not like a hydrogen
atom can lose itself

00:03:00.150 --> 00:03:01.670
or gain itself.

00:03:01.670 --> 00:03:03.870
And the reason why we said
that these two ideas are

00:03:03.870 --> 00:03:07.200
consistent is because if I'm
talking about a carbon and a

00:03:07.200 --> 00:03:09.530
carbon is losing a hydrogen.

00:03:09.530 --> 00:03:12.900
So let's say I have some
compound that looks like this.

00:03:12.900 --> 00:03:14.540
Maybe it's connected to a
bunch of other things

00:03:14.540 --> 00:03:15.530
someplace else.

00:03:15.530 --> 00:03:19.800
And then later on the carbon--
let's say I have a carbon that

00:03:19.800 --> 00:03:22.910
looks like that and I have an
oxygen that's maybe bound to

00:03:22.910 --> 00:03:23.710
another oxygen.

00:03:23.710 --> 00:03:27.020
I'm doing a very kind of
hand-wavy explanation here.

00:03:27.020 --> 00:03:30.180
And maybe that oxygen is bonded
to something else.

00:03:30.180 --> 00:03:31.730
This is what I start off with.

00:03:31.730 --> 00:03:34.130
And on the other side of this
equation I end up with

00:03:34.130 --> 00:03:35.910
something that looks
like this.

00:03:35.910 --> 00:03:38.760
Where a carbon is bonded
to an oxygen.

00:03:38.760 --> 00:03:42.600
And maybe that other oxygen is
bonded to this hydrogen.

00:03:42.600 --> 00:03:47.890
The biologist will say, oh, this
carbon has been oxidized

00:03:47.890 --> 00:03:50.590
because it lost its hydrogen.

00:03:50.590 --> 00:03:52.590
The hydrogen went from here--
I'll do it in a different

00:03:52.590 --> 00:03:56.120
color-- went from this carbon
to this oxygen.

00:03:56.120 --> 00:03:57.870
And the biologist would
also say that this

00:03:57.870 --> 00:04:00.540
oxygen has been reduced.

00:04:00.540 --> 00:04:03.510
It's been reduced because
it gained hydrogens.

00:04:03.510 --> 00:04:06.650
But the reality, or maybe the
chemists' definition, which I

00:04:06.650 --> 00:04:10.820
like a little bit more is, over
here because carbon is

00:04:10.820 --> 00:04:14.360
more electronegative, we
see carbon is much more

00:04:14.360 --> 00:04:15.440
electronegative than hydrogen.

00:04:15.440 --> 00:04:18.829
And oxygen is even more
electronegative than carbon.

00:04:18.829 --> 00:04:21.070
When any of these guys bond with
hydrogen they're going to

00:04:21.070 --> 00:04:22.860
hog the electron.

00:04:22.860 --> 00:04:25.170
So here, carbon got to
hog the electron.

00:04:25.170 --> 00:04:31.740
So here, carbon hogs
electrons.

00:04:31.740 --> 00:04:36.200
While here, carbon gets its
electrons hogged by oxygen.

00:04:36.200 --> 00:04:37.610
So here, oxygen hogs.

00:04:40.840 --> 00:04:43.850
So by losing the hydrogen, the
carbon actually lost its

00:04:43.850 --> 00:04:45.570
opportunity to hog electrons.

00:04:45.570 --> 00:04:47.930
And since it ended up bonding
with an oxygen, it not only

00:04:47.930 --> 00:04:50.610
can't hog hydrogen's electrons
but then it gets its electrons

00:04:50.610 --> 00:04:53.860
hogged by an even more
electronegative atom.

00:04:53.860 --> 00:04:55.920
So that's why these two
definitions are consistent.

00:04:55.920 --> 00:04:57.150
Same thing with the oxygen.

00:04:57.150 --> 00:04:59.695
Here it's bonding with another
oxygen, not hogging anything.

00:04:59.695 --> 00:05:04.130
But when it gains the hydrogen
it's able to

00:05:04.130 --> 00:05:06.020
hog hydrogen's electrons.

00:05:06.020 --> 00:05:08.290
Because it's so much more
electronegative.

00:05:08.290 --> 00:05:10.840
Or you could say that it's
gaining electrons.

00:05:10.840 --> 00:05:13.860
So that's why these two
definitions are somewhat

00:05:13.860 --> 00:05:14.370
consistent.

00:05:14.370 --> 00:05:16.270
Although sometimes they fall
apart if we're not dealing

00:05:16.270 --> 00:05:16.910
with hydrogen.

00:05:16.910 --> 00:05:21.080
The chemistry definition applies
more consistently to

00:05:21.080 --> 00:05:21.660
everything.

00:05:21.660 --> 00:05:24.190
But sometimes the biologists'
definition is easier to kind

00:05:24.190 --> 00:05:24.850
of glance at.

00:05:24.850 --> 00:05:27.210
Or you'll actually see it
written in textbooks.

00:05:27.210 --> 00:05:29.650
So let's go back to cellular
respiration and try to figure

00:05:29.650 --> 00:05:32.890
out what's being oxidized
and reduced.

00:05:32.890 --> 00:05:35.000
So if we look over here.

00:05:35.000 --> 00:05:37.160
Over here we have our glucose.

00:05:37.160 --> 00:05:40.610
And actually I copied and
pasted from Wikipedia a

00:05:40.610 --> 00:05:41.305
glucose molecule.

00:05:41.305 --> 00:05:42.405
And actually there's
one error here.

00:05:42.405 --> 00:05:44.060
And maybe I should edit
it on Wikipedia.

00:05:44.060 --> 00:05:47.830
There should be another hydrogen
bonded to that carbon

00:05:47.830 --> 00:05:48.720
right there.

00:05:48.720 --> 00:05:51.120
But as you see, all of the
hydrogens, they're either

00:05:51.120 --> 00:05:56.870
bonded to an oxygen or
a carbon over here.

00:05:56.870 --> 00:05:58.430
On the left-hand side, they're
either bonded to

00:05:58.430 --> 00:06:00.030
an oxygen or a carbon.

00:06:00.030 --> 00:06:02.760
If we were to write its
oxidation state, in every case

00:06:02.760 --> 00:06:04.580
it's bonded to something that's
more electronegative.

00:06:04.580 --> 00:06:07.060
So it's going to be giving
up its electrons.

00:06:07.060 --> 00:06:10.710
So it will have a plus
one oxidation state.

00:06:10.710 --> 00:06:12.880
And oxygen, in every case,
is either bonded to

00:06:12.880 --> 00:06:14.800
a carbon or a hydrogen.

00:06:14.800 --> 00:06:17.870
And so, oxygen, if it's bonded
to a carbon or a hydrogen, is

00:06:17.870 --> 00:06:20.520
going to hog an electron from
either one of those guys.

00:06:20.520 --> 00:06:25.010
So in every situation in
glucose, oxygen has a two

00:06:25.010 --> 00:06:27.940
minus or a minus two
oxidation state.

00:06:27.940 --> 00:06:31.090
And carbon, since this whole
thing is neutral, one would

00:06:31.090 --> 00:06:34.080
think that carbon would have
a neutral oxidation state.

00:06:34.080 --> 00:06:37.030
And if you go through this, you
actually find that most of

00:06:37.030 --> 00:06:39.140
these carbons do have neutral
oxidation states.

00:06:39.140 --> 00:06:41.080
Let me circle a few.

00:06:41.080 --> 00:06:44.710
So for example, this carbon
right here, it's hogging an

00:06:44.710 --> 00:06:46.500
electron from this hydrogen.

00:06:46.500 --> 00:06:49.210
But then it gets an electron
hogged by this oxygen.

00:06:49.210 --> 00:06:50.760
And then of course it does
nothing with the carbon.

00:06:50.760 --> 00:06:51.850
So that's neutral.

00:06:51.850 --> 00:06:53.710
This is neutral for
the same reason.

00:06:53.710 --> 00:06:56.810
This is neutral for
the same reason.

00:06:56.810 --> 00:06:59.330
This one is also neutral
for the same reason.

00:06:59.330 --> 00:07:01.130
It's bonded with two carbons.

00:07:01.130 --> 00:07:02.930
It has an electron
hogged by oxygen.

00:07:02.930 --> 00:07:05.360
But then it hogs an electron
from hydrogen.

00:07:05.360 --> 00:07:06.420
So it's neutral.

00:07:06.420 --> 00:07:08.370
So four of these carbons
are neutral.

00:07:08.370 --> 00:07:14.100
This carbon right here has two
electrons hogged by oxygens.

00:07:14.100 --> 00:07:17.910
And then it gets to take one
back from the hydrogen.

00:07:17.910 --> 00:07:19.760
So it has a plus one
oxidation state.

00:07:19.760 --> 00:07:20.410
This one is the opposite.

00:07:20.410 --> 00:07:22.520
It has two hydrogens
that it hogs from.

00:07:22.520 --> 00:07:24.940
Then it has to give one
away to the oxygen.

00:07:24.940 --> 00:07:26.340
So this has a minus one.

00:07:26.340 --> 00:07:27.870
So these two cancel out.

00:07:27.870 --> 00:07:31.120
On average, you can say that the
carbons in glucose have a

00:07:31.120 --> 00:07:32.910
neutral oxidation state.

00:07:32.910 --> 00:07:34.580
And I'm dealing with the
chemist definition.

00:07:34.580 --> 00:07:35.750
And I'm going to show you
that they're essentially

00:07:35.750 --> 00:07:36.920
equivalent.

00:07:36.920 --> 00:07:40.210
Here all of the oxygens have
no oxidation state.

00:07:40.210 --> 00:07:41.940
Because they're just bonded.

00:07:41.940 --> 00:07:44.420
Let me do it in a
better color.

00:07:44.420 --> 00:07:47.500
No oxidation state or neutral
oxidation state because

00:07:47.500 --> 00:07:48.690
they're double bonded
with oxygen.

00:07:48.690 --> 00:07:49.850
No one's hogging from anyone.

00:07:49.850 --> 00:07:52.800
They're obviously equally
electronegative.

00:07:52.800 --> 00:07:55.020
If we look at the
products, carbon

00:07:55.020 --> 00:07:56.340
dioxide looks like this.

00:07:56.340 --> 00:08:02.050
So, in either of these cases,
oxygen is hogging two

00:08:02.050 --> 00:08:03.810
electrons from this carbon.

00:08:03.810 --> 00:08:05.990
So it has a minus two
oxygen state.

00:08:05.990 --> 00:08:08.445
This oxygen is hogging two
electrons from carbon.

00:08:08.445 --> 00:08:10.600
So it has a minus two
oxidation state.

00:08:10.600 --> 00:08:13.480
And this carbon is getting all
of its valence electrons, all

00:08:13.480 --> 00:08:14.960
four, hogged by the oxygen.

00:08:14.960 --> 00:08:18.060
So it has a plus four
oxidation state.

00:08:18.060 --> 00:08:20.380
It's lost four electrons,
you can imagine.

00:08:20.380 --> 00:08:21.580
Because it's getting hogged.

00:08:21.580 --> 00:08:22.300
So that's carbon.

00:08:22.300 --> 00:08:24.950
So we could write this as four
plus for the carbon.

00:08:24.950 --> 00:08:27.160
And then each oxygen
has a two minus.

00:08:27.160 --> 00:08:29.190
And we can do the math later
on to figure out

00:08:29.190 --> 00:08:30.360
what the total is.

00:08:30.360 --> 00:08:32.669
And then, if we look at the
water-- we've looked at this

00:08:32.669 --> 00:08:36.239
before-- the oxygen is hogging
two electrons,

00:08:36.239 --> 00:08:39.020
one from each hydrogen.

00:08:39.020 --> 00:08:39.789
So two minus.

00:08:39.789 --> 00:08:41.990
And then each of the hydrogens
have a plus

00:08:41.990 --> 00:08:44.010
one oxidation state.

00:08:44.010 --> 00:08:47.800
So if you want to do a half
reaction for cellular

00:08:47.800 --> 00:08:50.710
respiration, and in the
chemists' sense of things,

00:08:50.710 --> 00:08:54.140
just dealing with electrons,
you can immediately say, I

00:08:54.140 --> 00:08:58.190
start with 12 hydrogens
on this side.

00:08:58.190 --> 00:08:59.760
Let me just write it this way.

00:08:59.760 --> 00:09:02.030
So H12 on this side.

00:09:02.030 --> 00:09:05.090
They all have a plus one
oxidation state.

00:09:05.090 --> 00:09:07.360
And then cellular respiration
occurs.

00:09:07.360 --> 00:09:08.890
And now I have 12 hydrogens.

00:09:08.890 --> 00:09:11.440
I could write the 12 a little
bit differently here.

00:09:11.440 --> 00:09:13.100
But they still have
a plus one.

00:09:13.100 --> 00:09:15.770
Each of them still has a plus
one oxidation state.

00:09:15.770 --> 00:09:18.870
So nothing from an oxidation
reduction point of view

00:09:18.870 --> 00:09:20.680
happens to the hydrogen.

00:09:20.680 --> 00:09:22.150
Now if we do the carbon.

00:09:25.060 --> 00:09:27.650
On the left-hand side of the
equation, we have six carbons.

00:09:27.650 --> 00:09:29.810
They have a neutral
oxidation state.

00:09:29.810 --> 00:09:31.220
But then on the right-hand
side of the

00:09:31.220 --> 00:09:32.900
equation, what happens?

00:09:32.900 --> 00:09:34.300
I now have six carbons.

00:09:34.300 --> 00:09:35.660
Written a little bit
differently.

00:09:35.660 --> 00:09:37.165
But I have six carbons.

00:09:37.165 --> 00:09:41.210
And they each have a plus
four oxidation state.

00:09:41.210 --> 00:09:44.350
Which means that they have
lost four electrons.

00:09:44.350 --> 00:09:46.880
Or their hypothetical charge,
by losing those four

00:09:46.880 --> 00:09:48.740
electrons, has gone
up by four.

00:09:48.740 --> 00:09:53.320
Because they're losing
negatively charged electrons.

00:09:53.320 --> 00:09:57.800
So the six carbons, after
cellular respiration, end up

00:09:57.800 --> 00:10:00.630
with six oxidized carbons,
with plus

00:10:00.630 --> 00:10:02.360
four oxidation states.

00:10:02.360 --> 00:10:05.390
Plus-- so each of these
lost four electrons.

00:10:05.390 --> 00:10:06.600
We have six of them.

00:10:06.600 --> 00:10:10.500
4 times 6 is 24 electrons.

00:10:10.500 --> 00:10:15.190
These are the electrons that the
carbon lost. So we see in

00:10:15.190 --> 00:10:17.730
cellular respiration that
the carbon is oxidized.

00:10:22.340 --> 00:10:24.490
Oxidation is losing electrons.

00:10:24.490 --> 00:10:26.620
We see in cellular respiration,
we draw the half

00:10:26.620 --> 00:10:30.490
reaction, carbon is losing, the
six carbons are losing a

00:10:30.490 --> 00:10:32.640
collective 24 electrons.

00:10:32.640 --> 00:10:37.320
And then finally, if I were to
do the oxygen on this side.

00:10:37.320 --> 00:10:39.890
I've lost my equation up here.

00:10:39.890 --> 00:10:41.670
So over here I have
two oxygens.

00:10:41.670 --> 00:10:43.300
And I'm going to draw them
a little bit separate.

00:10:43.300 --> 00:10:48.540
So I have these six oxygens
here that have a minus two

00:10:48.540 --> 00:10:50.290
oxidation state.

00:10:50.290 --> 00:10:52.050
On the left-hand side.

00:10:52.050 --> 00:10:53.040
So I'll draw it like this.

00:10:53.040 --> 00:10:55.580
They have a minus two
oxidation state.

00:10:55.580 --> 00:10:59.200
And then I have these
12 oxygens that

00:10:59.200 --> 00:11:00.450
are completely neutral.

00:11:06.630 --> 00:11:09.410
So I won't even write an
oxidation state or oxidation

00:11:09.410 --> 00:11:10.430
number there.

00:11:10.430 --> 00:11:12.930
And then after we
perform cellular

00:11:12.930 --> 00:11:15.540
respiration, what happens?

00:11:15.540 --> 00:11:21.400
Well now I have, in the carbon
dioxide, I have 12 carbons

00:11:21.400 --> 00:11:24.280
that have a minus two
oxidation state.

00:11:24.280 --> 00:11:25.030
Six times O2.

00:11:25.030 --> 00:11:29.350
So let me write that down
from the carbon dioxide.

00:11:29.350 --> 00:11:31.940
So I have six O2s that
all have a to

00:11:31.940 --> 00:11:34.210
minus oxidation state.

00:11:34.210 --> 00:11:37.990
And then I have another six
oxygens that have a minus two

00:11:37.990 --> 00:11:39.900
oxidation state.

00:11:39.900 --> 00:11:45.980
So plus six oxygens that have
a minus two oxidation state.

00:11:45.980 --> 00:11:48.820
So if you think about it, over
here I had a collective

00:11:48.820 --> 00:11:50.770
oxidation state on all
of the oxygens.

00:11:50.770 --> 00:11:51.380
These were neutral.

00:11:51.380 --> 00:11:54.730
I have 6 times minus 2,
that's a minus 12.

00:11:54.730 --> 00:11:56.870
You can kind of view it
as collective charge

00:11:56.870 --> 00:11:57.680
of all six of them.

00:11:57.680 --> 00:11:58.840
6 times minus 2.

00:11:58.840 --> 00:12:02.490
Here I have 6 times minus
2, which is minus 12.

00:12:02.490 --> 00:12:06.270
And then I have 6 times 2
oxygens per molecule.

00:12:06.270 --> 00:12:08.500
So that's 12 times minus 2.

00:12:08.500 --> 00:12:10.280
That's minus 24.

00:12:10.280 --> 00:12:14.060
So to go from a minus 12 to a
total oxidation or kind of

00:12:14.060 --> 00:12:16.850
hypothetical charge of
minus 36, I must

00:12:16.850 --> 00:12:20.790
have gained 24 electrons.

00:12:20.790 --> 00:12:24.690
And those 24 electrons that
I gained, that the oxygens

00:12:24.690 --> 00:12:28.070
gained, are the same 24
electrons that the carbons

00:12:28.070 --> 00:12:30.600
lost. So from the chemistry
point of

00:12:30.600 --> 00:12:32.210
view, it's very clear.

00:12:32.210 --> 00:12:33.750
Carbon was oxidized.

00:12:33.750 --> 00:12:41.120
And oxygen, which gained
electrons-- RIG.

00:12:41.120 --> 00:12:42.760
Reduction is gaining.

00:12:42.760 --> 00:12:45.160
Oxygen is reduced.

00:12:45.160 --> 00:12:46.240
And this is all a
bit of review.

00:12:46.240 --> 00:12:48.740
But it's nice to see it in
the context of cellular

00:12:48.740 --> 00:12:49.580
respiration.

00:12:49.580 --> 00:12:52.120
And this actually kind of
answers one of the questions

00:12:52.120 --> 00:12:56.060
of where does this
energy come from?

00:12:56.060 --> 00:12:58.860
In any of these chemical
reactions, when you see energy

00:12:58.860 --> 00:13:01.340
being produced, it's because
electrons are going from a

00:13:01.340 --> 00:13:04.120
higher energy state to
a lower energy state.

00:13:04.120 --> 00:13:08.620
If I have an electron that's up
here in a high energy state

00:13:08.620 --> 00:13:11.710
and it is able to go to a more
comfortable state, lower

00:13:11.710 --> 00:13:13.850
orbital or lower
energy orbital.

00:13:13.850 --> 00:13:16.840
So low energy or more
stable energy state.

00:13:16.840 --> 00:13:20.250
It'll generate energy in the
form of heat, or maybe this

00:13:20.250 --> 00:13:23.770
can do some work in some way,
help make ATP molecules.

00:13:23.770 --> 00:13:26.200
And so when you see these half
reactions, you see these 24

00:13:26.200 --> 00:13:29.550
electrons, that are being
lost by carbon,

00:13:29.550 --> 00:13:30.540
carbon is being oxidized.

00:13:30.540 --> 00:13:32.690
And they're going to oxygen.

00:13:32.690 --> 00:13:34.590
They're going in a whole
series of steps.

00:13:34.590 --> 00:13:36.880
It's not just happening
in one huge explosion.

00:13:36.880 --> 00:13:40.070
It's happening over a huge
series of steps.

00:13:40.070 --> 00:13:42.550
And as it does that, it's
entering lower and lower

00:13:42.550 --> 00:13:43.620
energy states.

00:13:43.620 --> 00:13:47.000
And as these electrons enter
the lower energy states,

00:13:47.000 --> 00:13:49.700
essentially by going from the
carbons and being pushed to

00:13:49.700 --> 00:13:52.730
the oxygens, that's where the
energy is coming from.

00:13:52.730 --> 00:13:56.060
That's where the energy
to make the 38

00:13:56.060 --> 00:13:57.590
ATPs is coming from.

00:13:57.590 --> 00:14:00.550
So, so far we talked a little
bit about how a

00:14:00.550 --> 00:14:01.890
chemist views oxidation.

00:14:01.890 --> 00:14:04.620
I touched at the beginning of
the video of how a biologist

00:14:04.620 --> 00:14:05.610
views oxidation.

00:14:05.610 --> 00:14:07.990
And then we saw that cellular
respiration from a chemist's

00:14:07.990 --> 00:14:10.810
point of view is clearly showing
that the carbon is

00:14:10.810 --> 00:14:13.240
being oxidized.

00:14:13.240 --> 00:14:15.730
It's losing electrons.

00:14:15.730 --> 00:14:17.610
And that the oxygen
is being reduced.

00:14:17.610 --> 00:14:19.190
It's gaining electrons.

00:14:19.190 --> 00:14:21.530
It's being reduced.

00:14:21.530 --> 00:14:24.760
That electrons are going from
this carbon and they're going,

00:14:24.760 --> 00:14:28.100
essentially, to these
oxygens right here.

00:14:28.100 --> 00:14:30.020
Now how does the biology
definition of our

00:14:30.020 --> 00:14:30.770
position hold up?

00:14:30.770 --> 00:14:32.580
Well here it holds
up pretty well.

00:14:32.580 --> 00:14:35.920
Because you can imagine, over
here, all of the hydrogens in

00:14:35.920 --> 00:14:39.490
the equation are associated
with glucose.

00:14:39.490 --> 00:14:43.300
And so they're either bonded,
if you look at the structure

00:14:43.300 --> 00:14:43.810
of glucose.

00:14:43.810 --> 00:14:47.650
The hydrogens are either bonded
to carbons or oxygens.

00:14:47.650 --> 00:14:50.350
So these are bonded to
carbons and oxygens.

00:14:50.350 --> 00:14:51.620
And when you go on the
right-hand side of the

00:14:51.620 --> 00:14:57.650
equation, all of the hydrogens
are only bonding with oxygen.

00:14:57.650 --> 00:15:01.570
So net-net, carbon definitely
lost hydrogens.

00:15:01.570 --> 00:15:05.130
And hydrogens and oxygen
definitely gained hydrogens.

00:15:05.130 --> 00:15:06.560
Let me write that down.

00:15:06.560 --> 00:15:08.740
We see in respiration, carbon
lost hydrogens.

00:15:14.760 --> 00:15:16.463
And oxygen gained hydrogens.

00:15:21.660 --> 00:15:23.020
And that's consistent.

00:15:23.020 --> 00:15:26.030
Because we see that by losing
hydrogens we are being

00:15:26.030 --> 00:15:27.970
oxidized from a biologist
point of view.

00:15:27.970 --> 00:15:31.800
And by gaining hydrogens,
oxygen is being reduced.

00:15:31.800 --> 00:15:34.120
And just so you can kind of
makes sense of this when you

00:15:34.120 --> 00:15:37.280
see this-- and when I start
drawing out the mechanisms,

00:15:37.280 --> 00:15:39.980
which I will hopefully not make
too hairy-- this process

00:15:39.980 --> 00:15:42.790
of transferring these hydrogens
is facilitated by

00:15:42.790 --> 00:15:46.480
molecules like NAD
plus and FAD.

00:15:46.480 --> 00:15:47.180
And we'll see that.

00:15:47.180 --> 00:15:50.600
But really, if we just want to
reconcile the two notions, as

00:15:50.600 --> 00:15:53.520
the hydrogens are being
transferred from one

00:15:53.520 --> 00:15:56.490
electronegative atom to another
electronegative atom,

00:15:56.490 --> 00:15:58.480
what's really being transferred
is the opportunity

00:15:58.480 --> 00:15:59.270
to hog electrons.

00:15:59.270 --> 00:16:02.320
If carbon has the hydrogen, it
gets to hog the electrons.

00:16:02.320 --> 00:16:04.670
But if that hydrogen goes from
the carbon-- and the whole

00:16:04.670 --> 00:16:07.070
atom; not just the nucleus, but
the whole atom goes to the

00:16:07.070 --> 00:16:10.110
oxygen-- now the oxygen
has gained that

00:16:10.110 --> 00:16:11.530
electron that it can hog.

00:16:11.530 --> 00:16:13.400
And carbon has lost
the electron.

00:16:13.400 --> 00:16:17.220
So carbon has oxidized and
oxygen has been reduced.

00:16:17.220 --> 00:16:18.760
And I mentioned this
in previous videos.

00:16:18.760 --> 00:16:20.380
But probably the most confusing
thing about

00:16:20.380 --> 00:16:23.840
oxidation is that you always
want to say, all right, that

00:16:23.840 --> 00:16:25.200
must have something
to do with oxygen.

00:16:25.200 --> 00:16:26.680
And it does.

00:16:26.680 --> 00:16:28.120
The word really comes
from, what would

00:16:28.120 --> 00:16:30.040
oxygen do to something?

00:16:30.040 --> 00:16:33.680
So oxygen, when it bonds with
things, it loses, it takes

00:16:33.680 --> 00:16:35.080
away their electrons.

00:16:35.080 --> 00:16:38.520
Or, in a reaction, it'll often
take away the hydrogens.

00:16:38.520 --> 00:16:39.920
It took away the hydrogens
from the

00:16:39.920 --> 00:16:41.780
carbon in this situation.

00:16:41.780 --> 00:16:43.510
So that's where the term
oxidation comes from.

00:16:43.510 --> 00:16:46.130
But you don't have to have
oxygen anywhere in your

00:16:46.130 --> 00:16:49.420
reaction for oxidation or
reduction to occur.

00:16:49.420 --> 00:16:51.580
Anyway, hopefully you found
that reasonably useful.

00:16:51.580 --> 00:16:54.960
This was actually a huge pain
point for me when I learned, I

00:16:54.960 --> 00:16:56.970
got comfortable with the
chemistry definition of

00:16:56.970 --> 00:16:58.230
oxidation reduction.

00:16:58.230 --> 00:16:59.970
And then all of a sudden you
open up your biology book and

00:16:59.970 --> 00:17:01.970
they start talking about losing
and gaining hydrogens,

00:17:01.970 --> 00:17:04.750
as opposed to electrons, and it
took me a while to really

00:17:04.750 --> 00:17:07.470
reconcile these two notions.


Oxidation and reduction review from biological point-of-view

WEBVTT
Kind: captions
Language: en

00:00:00.510 --> 00:00:02.900
What I want to do in this
video is review what we

00:00:02.900 --> 00:00:07.540
learned from our chemistry
classes about oxidation and

00:00:07.540 --> 00:00:10.450
the opposite of oxidation,
reduction.

00:00:10.450 --> 00:00:13.510
And then see how what we learned
in our chemistry class

00:00:13.510 --> 00:00:17.100
relates to the way that a
biologist or biochemist might

00:00:17.100 --> 00:00:17.960
use these words.

00:00:17.960 --> 00:00:20.270
And hopefully we'll see that
they're the same thing.

00:00:20.270 --> 00:00:22.450
So just as a bit of review, if
you watched the chemistry

00:00:22.450 --> 00:00:25.490
playlist. Oxidation, you can
view it-- and actually there's

00:00:25.490 --> 00:00:26.955
a famous mnemonic for it.

00:00:26.955 --> 00:00:35.980
It's: OIL RIG Where the oil
tells us that oxidation is

00:00:35.980 --> 00:00:38.940
losing-- I put it in quotes
because you're not necessarily

00:00:38.940 --> 00:00:41.430
losing the electrons; I'll
show you what I mean-- is

00:00:41.430 --> 00:00:43.380
losing electrons.

00:00:43.380 --> 00:00:44.630
This is what you should
have learned in

00:00:44.630 --> 00:00:46.650
your chemistry class.

00:00:46.650 --> 00:00:54.020
And then you also learned that
reduction is gaining.

00:00:54.020 --> 00:00:55.920
And I'll put that in
quotes as well.

00:00:55.920 --> 00:00:59.870
Is gaining electrons.

00:00:59.870 --> 00:01:02.180
And I put that in quotes because
you're not necessarily

00:01:02.180 --> 00:01:03.400
gaining electrons.

00:01:03.400 --> 00:01:04.860
You're more hogging it.

00:01:04.860 --> 00:01:07.180
And the reason why it's called
reduction, is because if you

00:01:07.180 --> 00:01:11.400
are gaining electrons your
notional charge, if you really

00:01:11.400 --> 00:01:13.940
were gaining them,
is being reduced.

00:01:13.940 --> 00:01:16.390
And the reason why this is
called oxidizing is because

00:01:16.390 --> 00:01:19.000
you tend to lose electrons
to oxygen.

00:01:19.000 --> 00:01:20.920
Although it doesn't
have to be oxygen.

00:01:20.920 --> 00:01:22.820
It could be any molecule
that will hog

00:01:22.820 --> 00:01:23.840
electrons away from you.

00:01:23.840 --> 00:01:28.150
And I think a nice example would
be fair to kind of make

00:01:28.150 --> 00:01:29.760
this a little bit
more concrete.

00:01:29.760 --> 00:01:33.770
Let's say I took some molecular
hydrogen, it's in a

00:01:33.770 --> 00:01:37.180
gaseous state, and I were to
combust that with some

00:01:37.180 --> 00:01:39.030
molecular oxygen.

00:01:39.030 --> 00:01:40.950
This is what happened
on the Hindenburg.

00:01:40.950 --> 00:01:43.470
They filled a balloon full of
hydrogen and you get a little

00:01:43.470 --> 00:01:45.630
bit of spark, expose it to
oxygen, and you're going to

00:01:45.630 --> 00:01:47.050
have a big explosion.

00:01:47.050 --> 00:01:50.040
But in the process, for every
mole of molecular oxygen, if

00:01:50.040 --> 00:01:53.060
you have two moles of molecular
hydrogen-- I'm just

00:01:53.060 --> 00:01:55.070
making sure the equation is
balanced-- you're going to

00:01:55.070 --> 00:02:01.070
produce two moles of H2O
plus a ton of heat.

00:02:01.070 --> 00:02:02.440
This thing is really
going to blow.

00:02:06.800 --> 00:02:08.229
What I want to do, I mean
we could talk about the

00:02:08.229 --> 00:02:10.190
Hindenburg but really, the whole
reason why I even wrote

00:02:10.190 --> 00:02:13.530
this is, I want to show you what
is getting oxidized and

00:02:13.530 --> 00:02:15.600
what is getting reduced.

00:02:15.600 --> 00:02:18.760
So in this situation right
here on the hydrogen, the

00:02:18.760 --> 00:02:20.630
molecular hydrogen just
looks like this.

00:02:20.630 --> 00:02:23.660
You have a hydrogen-hydrogen
bond.

00:02:23.660 --> 00:02:25.540
They're each sharing an electron
with the other one so

00:02:25.540 --> 00:02:27.840
that they both can pretend
their 1s orbital

00:02:27.840 --> 00:02:29.260
is completely filled.

00:02:29.260 --> 00:02:31.180
So they're not losing electrons
to each other.

00:02:31.180 --> 00:02:33.490
They're not hogging electrons
one from the other.

00:02:33.490 --> 00:02:35.500
So we say that they have a
neutral oxidative state.

00:02:35.500 --> 00:02:37.410
They haven't gained
or lost electrons.

00:02:37.410 --> 00:02:38.530
They're just sharing them.

00:02:38.530 --> 00:02:40.690
And the same thing is true
for the molecular oxygen.

00:02:40.690 --> 00:02:42.920
And here you actually
have a double bond

00:02:42.920 --> 00:02:43.890
with the two oxygens.

00:02:43.890 --> 00:02:46.310
But they're both oxygens, so
there's no reason why one

00:02:46.310 --> 00:02:49.240
would gain or lose electrons
from the other.

00:02:49.240 --> 00:02:53.590
But when you go on this side
of the equation, something

00:02:53.590 --> 00:02:54.440
interesting happens.

00:02:54.440 --> 00:02:58.080
You have, for every oxygen is
connected to two hydrogens.

00:03:02.060 --> 00:03:05.780
And the way to think about is
that oxygen is hogging each of

00:03:05.780 --> 00:03:07.640
these hydrogen's electrons.

00:03:07.640 --> 00:03:10.280
So hydrogen has this one
electron on its valence shell.

00:03:10.280 --> 00:03:12.910
The deal with most covalent
bonding is, hey, I give you an

00:03:12.910 --> 00:03:14.910
electron, you give me an
electron and we both have a

00:03:14.910 --> 00:03:15.930
complete pair.

00:03:15.930 --> 00:03:20.160
But we know, or hopefully we
can review, that oxygen is

00:03:20.160 --> 00:03:23.510
much more electronegative
than hydrogen.

00:03:23.510 --> 00:03:26.190
This is a little bit of glucose
that's left over from

00:03:26.190 --> 00:03:29.150
our cellular restoration
video.

00:03:29.150 --> 00:03:32.060
You can ignore it for now but
I'm going to connect all this

00:03:32.060 --> 00:03:32.870
in a future video.

00:03:32.870 --> 00:03:35.990
But if we look at our periodic
table, if you remember from

00:03:35.990 --> 00:03:39.510
the chemistry playlist,
electronegativity increases as

00:03:39.510 --> 00:03:42.470
we go to the top right of
the periodic table.

00:03:42.470 --> 00:03:46.210
These are the most
electronegative elements over

00:03:46.210 --> 00:03:48.680
here, these are the least
electronegative.

00:03:48.680 --> 00:03:51.240
And all electronegative means
is, likes to hog electrons.

00:04:03.730 --> 00:04:07.190
So even though oxygen and
hydrogen are in a covalent

00:04:07.190 --> 00:04:10.950
bond in water-- they're sharing
electrons-- oxygen is

00:04:10.950 --> 00:04:13.580
more electronegative, much
more electronegative than

00:04:13.580 --> 00:04:15.740
hydrogen, so it's going
to hog the electrons.

00:04:15.740 --> 00:04:18.019
And actually if you take some
elements on this side and you

00:04:18.019 --> 00:04:21.890
bond them with some guys over
here, these guys are so much

00:04:21.890 --> 00:04:24.080
more electronegative than these
left-hand elements that

00:04:24.080 --> 00:04:27.100
they'll actually completely
steal the electron, not just

00:04:27.100 --> 00:04:29.130
hog it for most of the time.

00:04:29.130 --> 00:04:30.990
But when you talk
electronegativity, it just

00:04:30.990 --> 00:04:33.410
means, likes the electrons.

00:04:33.410 --> 00:04:36.800
So when you look at this bond
between hydrogen and oxygen,

00:04:36.800 --> 00:04:39.300
we saw from the periodic table,
oxygen is a lot more

00:04:39.300 --> 00:04:42.280
electronegative, so the
electrons spend a lot more

00:04:42.280 --> 00:04:43.880
time on oxygen.

00:04:43.880 --> 00:04:46.190
We learned about hydrogen
bonding.

00:04:46.190 --> 00:04:49.780
We learned that it creates a
partial negative charge on

00:04:49.780 --> 00:04:52.630
that side of the water molecule
and creates partial

00:04:52.630 --> 00:04:54.810
positive charges on this side.

00:04:54.810 --> 00:04:56.760
And electrons still show
up around the hydrogens

00:04:56.760 --> 00:04:57.930
every now and then.

00:04:57.930 --> 00:05:01.460
When you talk about oxidation
and reduction you say, look

00:05:01.460 --> 00:05:03.130
there's no partial charge.

00:05:03.130 --> 00:05:07.110
If one guy is kind of hogging
the electron more, for the

00:05:07.110 --> 00:05:10.890
sake of oxidation states, we're
going to assume that he

00:05:10.890 --> 00:05:12.470
took the electron.

00:05:12.470 --> 00:05:16.580
So for an oxidation state, we'll
assume that the oxygen

00:05:16.580 --> 00:05:19.220
in water takes the electron
and we'll give him an

00:05:19.220 --> 00:05:22.740
oxidation state of one minus.

00:05:22.740 --> 00:05:25.600
Or the convention is, you write
the charge after the

00:05:25.600 --> 00:05:26.960
number for oxidation states.

00:05:26.960 --> 00:05:29.680
So you don't confuse it
with actual charges.

00:05:29.680 --> 00:05:32.210
So this has a one minus because,
from an oxidation

00:05:32.210 --> 00:05:34.110
state point of view, it's
taking the electron.

00:05:34.110 --> 00:05:35.620
It's gaining the elctron.

00:05:35.620 --> 00:05:36.950
That's why I put it in quotes.

00:05:36.950 --> 00:05:38.360
Because you're not really
gaining it.

00:05:38.360 --> 00:05:40.160
You're just gaining it
most of the time.

00:05:40.160 --> 00:05:42.190
You're hogging electrons.

00:05:42.190 --> 00:05:45.370
And likewise, this hydrogen--
let me be careful, this

00:05:45.370 --> 00:05:48.440
isn't-- he got one electron from
this hydrogen and you got

00:05:48.440 --> 00:05:49.950
another electron from
this hydrogen.

00:05:49.950 --> 00:05:52.890
So instead of saying one minus,
it should be two minus.

00:05:52.890 --> 00:05:55.590
It should be two minus, because
he's hogging one

00:05:55.590 --> 00:05:58.140
electron from here and one
electron from there.

00:05:58.140 --> 00:06:02.570
And in general, when oxygen is
bonding with other non-oxygen

00:06:02.570 --> 00:06:06.980
atoms or non-oxygen elements,
it tends to have a two minus

00:06:06.980 --> 00:06:10.050
or a negative two
oxidation state.

00:06:10.050 --> 00:06:11.850
So if this guy's two
minus, because

00:06:11.850 --> 00:06:14.250
he's gained two electrons.

00:06:14.250 --> 00:06:15.870
Let me write that in quotes.

00:06:15.870 --> 00:06:18.710
Gained two electrons.

00:06:18.710 --> 00:06:20.920
We know that he really didn't
gain them, that he's just

00:06:20.920 --> 00:06:21.840
hogging them.

00:06:21.840 --> 00:06:24.790
These guys lost an
electron each.

00:06:24.790 --> 00:06:28.240
So this guy's oxidation state
is going to be one plus.

00:06:28.240 --> 00:06:32.840
And this guy's oxidation state
is going to be one plus.

00:06:32.840 --> 00:06:35.930
So you could say, by combusting
the hydrogen with

00:06:35.930 --> 00:06:39.060
the oxygen, that the hydrogens--
before they had a

00:06:39.060 --> 00:06:42.120
zero oxygen state, each of these
hydrogens had a zero

00:06:42.120 --> 00:06:45.410
oxygen state-- now they have
a one plus oxidation state

00:06:45.410 --> 00:06:47.660
because they lost their
electrons when they bonded

00:06:47.660 --> 00:06:48.660
with the oxygen.

00:06:48.660 --> 00:06:51.540
So we say that these hydrogens
have been oxidized.

00:06:56.790 --> 00:07:05.270
So, due to this reaction,
hydrogen has been oxidized.

00:07:05.270 --> 00:07:06.880
Why has it been oxidized?

00:07:06.880 --> 00:07:08.720
Because before, it was
able to share its

00:07:08.720 --> 00:07:10.240
electrons very nicely.

00:07:10.240 --> 00:07:13.210
But then it bonds with oxygen,
which will hog its electrons.

00:07:13.210 --> 00:07:16.780
So the hydrogen is losing its
electrons to the oxygen, so

00:07:16.780 --> 00:07:18.320
it's been oxidized.

00:07:18.320 --> 00:07:25.270
Similarly, the oxygen, due to
this combustion reaction, has

00:07:25.270 --> 00:07:31.070
been reduced.

00:07:31.070 --> 00:07:32.130
Why has it been reduced?

00:07:32.130 --> 00:07:33.850
Here it was just sharing
electrons.

00:07:33.850 --> 00:07:35.330
It wasn't losing
or gaining it.

00:07:35.330 --> 00:07:39.590
But here when it's bonded with
an element with much lower

00:07:39.590 --> 00:07:42.460
electronegativity, all of a
sudden it can start hogging

00:07:42.460 --> 00:07:44.450
the electrons, it
gains electrons.

00:07:44.450 --> 00:07:47.785
So this hypothetical charge
is reduced by two.

00:07:50.410 --> 00:07:53.050
And if I wanted to actually
account for all of the

00:07:53.050 --> 00:07:55.170
electrons, because we're talking
about losing electrons

00:07:55.170 --> 00:07:58.710
and gaining electrons, we can
write two half reactions.

00:07:58.710 --> 00:08:00.280
This should all be a little
bit of review from your

00:08:00.280 --> 00:08:01.030
chemistry class.

00:08:01.030 --> 00:08:02.780
But it never hurts to
see this again.

00:08:02.780 --> 00:08:05.000
I'm going to throw this in the
biology playlist so that you

00:08:05.000 --> 00:08:08.270
biology people can hopefully
refresh your

00:08:08.270 --> 00:08:10.010
memory with this stuff.

00:08:10.010 --> 00:08:11.440
We can write two
half reactions.

00:08:11.440 --> 00:08:15.840
We could say that we started
off with two moles of

00:08:15.840 --> 00:08:17.150
molecular hydrogen.

00:08:17.150 --> 00:08:21.150
And they have no oxidation
states, or they're neutral.

00:08:21.150 --> 00:08:23.010
So I could write a zero
there if I want.

00:08:23.010 --> 00:08:26.020
And then I end up with-- on the
other side-- I end up with

00:08:26.020 --> 00:08:29.340
two moles of H2.

00:08:29.340 --> 00:08:33.760
But each of the hydrogens
now, have a plus

00:08:33.760 --> 00:08:35.010
one oxidation state.

00:08:39.179 --> 00:08:41.580
Or another way to think about it
is, each of these-- there's

00:08:41.580 --> 00:08:42.940
four hydrogens here.

00:08:42.940 --> 00:08:45.380
This is molecular hydrogen has
two hydrogens and we have two

00:08:45.380 --> 00:08:46.050
moles of this.

00:08:46.050 --> 00:08:47.650
So there are four
hydrogens here.

00:08:47.650 --> 00:08:50.480
Each of the four hydrogens
lost an electron.

00:08:50.480 --> 00:08:51.160
So I can write this.

00:08:51.160 --> 00:08:54.530
So, plus four electrons.

00:08:54.530 --> 00:08:56.460
That's the half reaction
for hydrogen.

00:08:56.460 --> 00:08:58.640
It lost four electrons.

00:08:58.640 --> 00:09:05.300
So this is another way of
saying that hydrogen is

00:09:05.300 --> 00:09:09.000
oxidized because it
lost electrons.

00:09:09.000 --> 00:09:11.200
OIL: oxidation is losing.

00:09:11.200 --> 00:09:15.470
And then the other half
reaction, if I were to write

00:09:15.470 --> 00:09:16.750
the oxygen.

00:09:16.750 --> 00:09:21.640
So I'm starting with a mole of
molecular oxygen and I'm

00:09:21.640 --> 00:09:24.570
adding to that four electrons.

00:09:24.570 --> 00:09:25.970
I can't make electrons
out of nowhere.

00:09:25.970 --> 00:09:28.040
I'm getting the electrons from
the hydrogen, I'm adding to

00:09:28.040 --> 00:09:29.240
the oxygen.

00:09:29.240 --> 00:09:35.560
And so the half reaction on this
side, I end up with two

00:09:35.560 --> 00:09:38.650
moles-- I could write it like
this-- two moles of oxygen.

00:09:38.650 --> 00:09:43.840
And each of them have an
oxidation state of two minus.

00:09:43.840 --> 00:09:45.080
So these are the
half reactions.

00:09:45.080 --> 00:09:47.630
And all this is showing is that
the hydrogen, over the

00:09:47.630 --> 00:09:50.310
course of this combustion
reaction, lost electrons.

00:09:50.310 --> 00:09:53.830
And that the oxygen gained the
electrons that the hydrogen

00:09:53.830 --> 00:10:02.370
lost. So this tells us that
oxygen is reduced.

00:10:02.370 --> 00:10:05.120
Now this is all fair and good
and this is all a bit of

00:10:05.120 --> 00:10:07.410
review of what you learned
in chemistry class.

00:10:07.410 --> 00:10:09.520
But now I'm going to make things
even more confusing.

00:10:09.520 --> 00:10:11.770
Because I'm going to introduce
you to how a biologist

00:10:11.770 --> 00:10:12.730
thinks about it.

00:10:12.730 --> 00:10:14.350
So-- and it's not
always the case.

00:10:14.350 --> 00:10:16.440
Sometimes the biologist will use
the definition you learned

00:10:16.440 --> 00:10:17.720
in your chemistry class.

00:10:17.720 --> 00:10:20.710
But a biologist-- or many
times in many biology

00:10:20.710 --> 00:10:23.915
textbooks-- they'll say-- and
this used to confuse me to no

00:10:23.915 --> 00:10:39.220
end, really-- that oxidation is
losing hydrogen atoms. And

00:10:39.220 --> 00:10:52.210
reduction is gaining
hydrogen atoms.

00:10:52.210 --> 00:10:54.570
And at first when I got exposed
to this, I was like, I

00:10:54.570 --> 00:10:57.190
learned it in chemistry class
and they talk about electrons.

00:10:57.190 --> 00:11:00.280
Hydrogen atoms, you know it's a
proton and an electron, how

00:11:00.280 --> 00:11:01.130
does it relate?

00:11:01.130 --> 00:11:03.550
And the reason why these two
definitions-- this is really

00:11:03.550 --> 00:11:05.460
the whole point of this video--
the reason why this

00:11:05.460 --> 00:11:09.580
definition is consistent with
this one is because in the

00:11:09.580 --> 00:11:21.190
biological world hydrogen
is what tends

00:11:21.190 --> 00:11:22.230
to get swapped around.

00:11:22.230 --> 00:11:27.970
And it tends to bond with
carbon, oxygen,

00:11:27.970 --> 00:11:30.500
phosphorous, nitrogen.

00:11:30.500 --> 00:11:35.570
And if we look at the periodic
table, and we see where

00:11:35.570 --> 00:11:40.840
hydrogen is, and we see where
carbon, nitrogen, oxygen and

00:11:40.840 --> 00:11:43.700
phosphorous and really all this
other stuff is, you see

00:11:43.700 --> 00:11:46.840
that all of the stuff that in
biological systems, hydrogen

00:11:46.840 --> 00:11:50.570
tends to bond with, the things
it tends to bond with are

00:11:50.570 --> 00:11:52.920
much, much more electronegative.

00:11:52.920 --> 00:11:56.270
So if a carbon is bonding with
a hydrogen, the carbon is

00:11:56.270 --> 00:11:57.740
hogging that electron.

00:11:57.740 --> 00:12:00.610
And then if that hydrogen gets
transferred to an oxygen,

00:12:00.610 --> 00:12:04.260
along with the electron, the
carbon will lose the hydrogen

00:12:04.260 --> 00:12:06.220
atom, but it really lost
the electron that

00:12:06.220 --> 00:12:07.450
it was hogging before.

00:12:07.450 --> 00:12:09.940
And now the oxygen can
hog that electron.

00:12:09.940 --> 00:12:11.990
So these are really consistent
definitions.

00:12:11.990 --> 00:12:13.690
And the whole reason why I
showed you this example is

00:12:13.690 --> 00:12:17.760
because the biological
definition doesn't apply here.

00:12:17.760 --> 00:12:21.900
I mean, you could say, well,
oxygen is definitely gaining

00:12:21.900 --> 00:12:23.650
hydrogens in this reaction.

00:12:23.650 --> 00:12:27.000
So we can definitely say that
oxygen is being reduced still,

00:12:27.000 --> 00:12:30.110
according to the biological
definition.

00:12:30.110 --> 00:12:32.780
But you can't really say
that hydrogen is

00:12:32.780 --> 00:12:34.740
losing hydrogens here.

00:12:34.740 --> 00:12:37.840
In this situation, hydrogen
is just losing electrons.

00:12:37.840 --> 00:12:39.290
It's not losing itself.

00:12:39.290 --> 00:12:41.120
I guess you could say it's
losing itself because it's

00:12:41.120 --> 00:12:42.090
being taken over.

00:12:42.090 --> 00:12:43.920
But the biological definition
just comes

00:12:43.920 --> 00:12:44.830
from the same notion.

00:12:44.830 --> 00:12:48.450
That when hydrogen bonds with
most things in biological

00:12:48.450 --> 00:12:51.520
compounds, it tends to
give the electrons.

00:12:51.520 --> 00:12:53.740
So if a carbon loses a hydrogen
and gives it to an

00:12:53.740 --> 00:12:56.940
oxygen, the carbon will lose
that hydrogen's electron that

00:12:56.940 --> 00:12:58.170
it was able to hog.

00:12:58.170 --> 00:12:59.850
And now the oxygen
is hogging it.

00:12:59.850 --> 00:13:03.500
So the carbon would be oxidized
and the oxygen would

00:13:03.500 --> 00:13:04.370
be reduced.

00:13:04.370 --> 00:13:05.310
Hope that doesn't confuse you.

00:13:05.310 --> 00:13:07.820
In the next video I'll show you
a couple more examples.

00:13:07.820 --> 00:13:10.630
And the whole reason why I'm
doing this is to apply this to

00:13:10.630 --> 00:13:12.090
cellular respiration.

00:13:12.090 --> 00:13:14.350
So that you don't get confused
when people talk and say that,

00:13:14.350 --> 00:13:20.710
oh the NAD is being reduced when
it picks up the hydrogen.

00:13:20.710 --> 00:13:23.310
Or it's being oxidized when it
loses the hydrogen, and so

00:13:23.310 --> 00:13:23.980
forth and so on.

00:13:23.980 --> 00:13:26.030
I wanted you to see that these
are the same definitions that

00:13:26.030 --> 00:13:28.540
you learned in your
chemistry class.