2015 AP Physics 1 free response 1b

WEBVTT
Kind: captions
Language: en

00:00:00.098 --> 00:00:02.737
- Alright, let's tackle part b, now.

00:00:02.737 --> 00:00:06.916
Derive the magnitude of the
acceleration of block 2.

00:00:06.916 --> 00:00:11.916
Express your answer in
terms of m1, m2, and g.

00:00:12.176 --> 00:00:13.988
And like always, try to pause the video

00:00:13.988 --> 00:00:15.428
and see if you can work
through it yourself.

00:00:15.428 --> 00:00:18.740
We already worked through
part 1, or part a,

00:00:18.740 --> 00:00:21.480
I should say, based on this diagram above,

00:00:21.480 --> 00:00:22.326
and there's a previous video.

00:00:22.326 --> 00:00:24.857
So, now we're ready to do part b.

00:00:24.857 --> 00:00:27.959
And we've already drawn
the free-body diagrams,

00:00:27.959 --> 00:00:31.709
which will help us determine
the acceleration of block 2.

00:00:31.709 --> 00:00:34.170
Let's just think about what
the acceleration is, first.

00:00:34.170 --> 00:00:36.198
We know it's going to
accelerate downwards,

00:00:36.198 --> 00:00:38.706
because, there's a couple
ways you can think about it,

00:00:38.706 --> 00:00:42.854
the weight of block 2 is larger
than the weight of block 1,

00:00:42.854 --> 00:00:44.379
they're connected by the
string, so we know we're gonna

00:00:44.379 --> 00:00:46.577
accelerate downwards on
the right-hand side and

00:00:46.577 --> 00:00:48.655
upwards on the left-hand side.

00:00:48.655 --> 00:00:49.758
The other way to think about it, is

00:00:49.758 --> 00:00:52.358
the weight of block 2 is
larger than the upward force of

00:00:52.358 --> 00:00:57.358
tension. And the weight of
block 1 is less than the

00:00:57.583 --> 00:00:59.939
tension pulling upwards.

00:00:59.939 --> 00:01:01.094
So, you're gonna accelerate upwards on the

00:01:01.094 --> 00:01:03.976
left-hand side, accelerate
downwards on the right-hand side

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and a key realization is,

00:01:05.423 --> 00:01:08.653
the magnitude of the acceleration
is going to be the same

00:01:08.653 --> 00:01:11.667
because they're connected by that string.

00:01:11.667 --> 00:01:16.033
So, the acceleration, I'll
just draw it a little bit away

00:01:16.033 --> 00:01:20.128
from the actual dot, so
the acceleration, here,

00:01:20.128 --> 00:01:23.309
has a magnitude a, it's gonna
go in the downward direction

00:01:23.309 --> 00:01:26.403
the acceleration on the left-hand
side is gonna be the same

00:01:26.403 --> 00:01:30.199
magnitude, but it's gonna
go in the upwards direction.

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So that just gives us a sense of things.

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They say, derive the magnitude
of acceleration of block 2

00:01:36.471 --> 00:01:37.330
Alright, so this is,

00:01:37.330 --> 00:01:39.419
let me leave the labels up there,

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so this is block 2 up here.

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And we know, from Newton's 2nd Law,

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that if we pick a direction,
and the direction that matters

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here, is the vertical direction.

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All the forces are acting in

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either the upwards or downwards direction.

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So, the magnitude of our net forces,

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we care about the vertical dimension here,

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is going to be equal to the
mass times the acceleration,

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in that, in that dimension,
in that direction,

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I guess you could say.

00:02:06.101 --> 00:02:09.038
And so let's just think about block 2.

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Block, Block 2.

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And since the acceleration,
we know is downwards,

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and we wanna figure out what a is,

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let's just assume that positive,

00:02:21.284 --> 00:02:24.918
positive magnitude specifies downwards.

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So what are the net forces?

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Well, the net forces are going
to be the force of weight

00:02:29.990 --> 00:02:32.675
minus the tension, and
that's going to be positive.

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If we think about it in
the downward direction.

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The downward direction being positive.

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So we're gonna have m2g, the weight,

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minus the tension,

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tension is going against the weight,

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minus the tension is going
to be equal to the mass.

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Is going to be equal to m2
times, times our acceleration,

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and we need to figure out
what that acceleration

00:02:57.468 --> 00:03:00.123
is going to be.

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So, we do that same blue color.

00:03:02.401 --> 00:03:06.059
Times the acceleration.

00:03:06.059 --> 00:03:08.353
Now, we could divide both sides by m2,

00:03:08.353 --> 00:03:10.559
but that's not going to
help us too much, just yet.

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Because then, we would've
solved for acceleration in terms

00:03:12.719 --> 00:03:17.719
of m2g and T.

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We don't have any m1s here, so
we're not solving in terms of

00:03:21.149 --> 00:03:22.823
m1, m2, and g.

00:03:22.823 --> 00:03:26.411
We're solving in terms of m2, T, and g.

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So, somehow, we have to get rid of this T.

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And what we can do to get rid of the T,

00:03:31.089 --> 00:03:34.270
is set up a similar equation for block 1.

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Block 1, Block 1

00:03:39.703 --> 00:03:42.397
Here, since we're concerned
with magnitude and

00:03:42.397 --> 00:03:44.218
especially the magnitude
of acceleration, and

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here the acceleration is
going in the upward direction,

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we could say that the upward direction

00:03:47.656 --> 00:03:49.327
is the positive direction.

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And so, we could say that T

00:03:52.391 --> 00:03:53.854
minus, we know that the tension is

00:03:53.854 --> 00:03:55.152
larger than the weight,

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T minus m1g is going to be equal to

00:04:01.272 --> 00:04:04.411
is equal to m1,

00:04:04.411 --> 00:04:09.411
is going to be equal to
m1 times the magnitude of

00:04:11.071 --> 00:04:11.977
the acceleration.

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And to be clear, these
magnitudes are the same.

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And we already know that the
magnitudes of the tension

00:04:16.854 --> 00:04:18.014
are the same.

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And now we have two equations

00:04:19.938 --> 00:04:21.420
with two unknowns,

00:04:21.420 --> 00:04:23.440
and so, if we can eliminate the tension,

00:04:23.440 --> 00:04:25.714
we can solve for acceleration.

00:04:25.714 --> 00:04:27.596
And we can acutally do that by just

00:04:27.596 --> 00:04:29.361
adding the left-hand side
to the left-hand side,

00:04:29.361 --> 00:04:32.159
and the right-hand side
to the right-hand side.

00:04:32.159 --> 00:04:37.159
You learned this probably
first in algebra 1. If,

00:04:37.471 --> 00:04:40.306
if this is equal to that
and that is equal to that,

00:04:40.306 --> 00:04:42.315
if we add the left side to the left side

00:04:42.315 --> 00:04:43.438
and the right side to the right side,

00:04:43.438 --> 00:04:44.944
well, we're still gonna
get two things that are

00:04:44.944 --> 00:04:46.313
equal to each other.

00:04:46.313 --> 00:04:48.971
So when you add the left-hand sides,

00:04:48.971 --> 00:04:50.272
what are you going to get?

00:04:50.272 --> 00:04:55.224
So, you're gonna get m2g,

00:04:55.224 --> 00:05:00.034
m2g minus m1g,

00:05:00.034 --> 00:05:03.402
minus m1g,

00:05:03.402 --> 00:05:06.675
and then you're gonna get T minus T.

00:05:06.675 --> 00:05:08.100
These two are going to cancel out.

00:05:08.100 --> 00:05:09.548
So, let me just cross them out.

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So that was convenient.

00:05:11.093 --> 00:05:13.323
Is going to be equal to

00:05:13.323 --> 00:05:18.323
m2a, is going to be equal to m2a

00:05:18.468 --> 00:05:20.755
plus m1a,

00:05:20.755 --> 00:05:25.755
plus m1 times a.

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And now, we just need to solve for a.

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And how do we do that?

00:05:29.811 --> 00:05:32.228
Well, we can factor out an a
out of this right-hand side

00:05:32.228 --> 00:05:37.228
here, so this going to be m2g minus m1g

00:05:39.616 --> 00:05:41.090
is equal to

00:05:41.090 --> 00:05:42.681
let's factor out an a,

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a times, times m2 plus m1,

00:05:50.030 --> 00:05:50.870
and now to solve for a,

00:05:50.870 --> 00:05:54.225
we just divide both sides by m2 plus m1.

00:05:54.225 --> 00:05:56.303
m2 plus m1,

00:05:56.303 --> 00:06:01.179
m2 plus m1,

00:06:01.179 --> 00:06:02.498
and there you have it, we get a

00:06:02.498 --> 00:06:04.040
is equal to

00:06:04.040 --> 00:06:05.552
a is equal to this.

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And, notice, we have solved it,

00:06:06.413 --> 00:06:08.586
we have solved for a in terms of

00:06:08.586 --> 00:06:10.502
we have solved for a in terms of

00:06:10.502 --> 00:06:13.323
m1, m2, and g.

00:06:13.323 --> 00:06:15.889
And this is the magnitude of
the acceleration of either

00:06:15.889 --> 00:06:18.548
block 1 or block 2.

00:06:18.548 --> 00:06:19.592
Now, some of you might be thinking,

00:06:19.592 --> 00:06:21.670
wait, there might be an
easier way to think about this

00:06:21.670 --> 00:06:24.751
problem, and I went straight
from the free-body diagrams

00:06:24.751 --> 00:06:27.197
which is, ya know, it's
implied that this is

00:06:27.197 --> 00:06:29.960
the way to tackle it, using the tension.

00:06:29.960 --> 00:06:31.388
But, another way to tackle it,

00:06:31.388 --> 00:06:32.538
you could've said, well,

00:06:32.538 --> 00:06:34.256
this would be analogous, it's not the

00:06:34.256 --> 00:06:35.893
exact same thing, but
it would be analogous

00:06:35.893 --> 00:06:39.968
to imagine, two, these two
blocks floating in space.

00:06:39.968 --> 00:06:42.255
So, this is m2, here, and I'm not gonna

00:06:42.255 --> 00:06:44.914
use pulleys here, so that's m2.

00:06:44.914 --> 00:06:46.667
And it's connected by

00:06:46.667 --> 00:06:49.070
a massless string,

00:06:49.070 --> 00:06:54.070
to m1, which has a smaller mass, m1.

00:06:54.608 --> 00:06:58.788
And let's say that you
are pulling on, pulling

00:06:58.788 --> 00:07:00.378
in the rightward direction, now we're just

00:07:00.378 --> 00:07:02.861
drifting in space.

00:07:02.861 --> 00:07:06.983
With a force of m2g, we're not,

00:07:06.983 --> 00:07:09.839
we just care about the magnitude here, and

00:07:09.839 --> 00:07:11.429
I know you might be saying, wait, okay,

00:07:11.429 --> 00:07:14.332
is this is the gravitational
field or whatever else,

00:07:14.332 --> 00:07:15.655
but I'm saying, let's
just say you're pulling

00:07:15.655 --> 00:07:17.164
in this direction with a force

00:07:17.164 --> 00:07:20.949
that happens to be equal to,
that has a magnitude of m2g,

00:07:20.949 --> 00:07:24.762
and let's say you're
pulling in this direction,

00:07:24.762 --> 00:07:29.762
with a force that has
a magnitude of m1, m1g.

00:07:30.936 --> 00:07:33.916
Now, this isn't exactly the
same as our, as where we started

00:07:33.916 --> 00:07:37.144
where we started, we saw what
I have just kind of drawn,

00:07:37.144 --> 00:07:39.356
but I have it in the presence
of a gravitational field,

00:07:39.356 --> 00:07:41.028
and I have it wrapped
around those pulleys,

00:07:41.028 --> 00:07:44.093
and then the gravitational
field is providing these forces.

00:07:44.093 --> 00:07:46.205
But let's just assume,
just for simplicity that

00:07:46.205 --> 00:07:47.808
that you're drifting in space and you're

00:07:47.808 --> 00:07:50.014
pulling on m2 to the
right with a force that's

00:07:50.014 --> 00:07:52.951
equivalent to m2g, and you
are pulling to the left

00:07:52.951 --> 00:07:55.842
on m1, with a force of m1g.

00:07:55.842 --> 00:07:58.812
Well, you could just view this as one big,

00:07:58.812 --> 00:08:02.820
you could just view the m1,
the string, and m2 as just

00:08:02.820 --> 00:08:05.397
one combined mass.

00:08:05.397 --> 00:08:07.881
You could just view this
as one combined mass,

00:08:07.881 --> 00:08:12.346
of m1 plus m2, and you could say, alright,

00:08:12.346 --> 00:08:14.662
well from that one combined mass,

00:08:14.662 --> 00:08:15.940
I am,

00:08:15.940 --> 00:08:16.949
whoops,

00:08:16.949 --> 00:08:20.721
that one combined mass, I am

00:08:20.721 --> 00:08:24.537
I am pulling to the right
with a magnitude of m2g,

00:08:24.537 --> 00:08:27.350
and I am pulling to the left

00:08:27.350 --> 00:08:29.154
let me make that a
slightly different color

00:08:29.154 --> 00:08:30.562
so you can see it.

00:08:30.562 --> 00:08:35.562
And I am pulling to the
left with a magnitude of m1g

00:08:37.043 --> 00:08:39.482
and now, this becomes a
pretty straight-forward thing.

00:08:39.482 --> 00:08:40.880
What would be the acceleration here?

00:08:40.880 --> 00:08:42.842
Well, you could say the net,

00:08:42.842 --> 00:08:46.403
the net magnitude of the force,

00:08:46.403 --> 00:08:48.071
or the magnitude of the net force would be

00:08:48.071 --> 00:08:50.846
m2g, we'll take the rightward direction as

00:08:50.846 --> 00:08:55.846
the positive direction, m2g minus m1g

00:08:56.117 --> 00:09:00.064
minus m1g, and then, so
that's the net force,

00:09:00.064 --> 00:09:01.504
in the right direction,

00:09:01.504 --> 00:09:03.826
the magnitude of the net force
in the rightward direction

00:09:03.826 --> 00:09:05.081
and then you divide it by its mass,

00:09:05.081 --> 00:09:06.624
and you're gonna get acceleration.

00:09:06.624 --> 00:09:08.979
Force divided by mass
gives you acceleration.

00:09:08.979 --> 00:09:13.979
So, you divide that by our
mass, which is going to be

00:09:14.077 --> 00:09:18.083
which is going to be m1 plus m2,

00:09:18.083 --> 00:09:21.020
that's going to give
you your acceleration.

00:09:21.020 --> 00:09:22.928
So, you could view this as a simpler way

00:09:22.928 --> 00:09:24.279
of thinking about it. But they,

00:09:24.279 --> 00:09:28.179
notice, either of them give
you the exact same answer.

00:09:28.179 --> 00:09:30.630
That's one of the fun
things about science,

00:09:30.630 --> 00:09:32.509
as long as you do logical things,

00:09:32.509 --> 00:09:34.839
you get to the same point.


2015 AP Physics 1 free response 1a

WEBVTT
Kind: captions
Language: en

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- [Voiceover] Two blocks are connected by

00:00:01.920 --> 00:00:03.963
a string of negligible mass that passes

00:00:03.963 --> 00:00:06.472
over massless pulleys that turn with

00:00:06.472 --> 00:00:07.981
negligible friction, as shown in

00:00:07.981 --> 00:00:10.431
the figure above, we see that there.

00:00:10.431 --> 00:00:14.228
The mass m2 of block 2 is greater

00:00:14.228 --> 00:00:17.026
than the mass m1 of block 1.

00:00:17.026 --> 00:00:20.149
The blocks are released from rest.

00:00:20.149 --> 00:00:21.402
So let's just really quick think about

00:00:21.402 --> 00:00:23.642
what we think is going to happen here.

00:00:23.642 --> 00:00:26.090
Block 2 has a larger
mass, they're connected

00:00:26.090 --> 00:00:29.726
by this string and pulley system here.

00:00:29.726 --> 00:00:31.166
Well if it has a larger
mass, they're in the

00:00:31.166 --> 00:00:32.803
same gravitational
field, it's going to have

00:00:32.803 --> 00:00:35.090
a larger weight and so the weight

00:00:35.090 --> 00:00:36.669
pulling down on block 2 is going to be

00:00:36.669 --> 00:00:40.245
larger than the weight
pulling down on block 1

00:00:40.245 --> 00:00:41.742
and so you're going to have block 2

00:00:41.742 --> 00:00:43.983
accelerating downwards, you're going

00:00:43.983 --> 00:00:47.129
to have block 2 accelerating downwards

00:00:47.129 --> 00:00:49.150
and block 1 is going to accelerate upwards

00:00:49.150 --> 00:00:51.309
with the same magnitude.

00:00:51.309 --> 00:00:54.735
So block 1 is going to accelerate upwards

00:00:54.735 --> 00:00:56.371
and so with that just intuition

00:00:56.371 --> 00:00:58.008
of what we think is going to happen here

00:00:58.008 --> 00:01:00.968
let's try to tackle part A of this.

00:01:00.968 --> 00:01:03.849
So they tell us the
dots below, these dots,

00:01:03.849 --> 00:01:05.997
represent the two blocks, so this

00:01:05.997 --> 00:01:08.876
represents block 1,
this represents block 2.

00:01:08.876 --> 00:01:11.069
Draw free-body diagrams
showing and labeling

00:01:11.069 --> 00:01:14.494
the forces, not components,
exerted on each block.

00:01:14.494 --> 00:01:16.793
Draw the relative lengths of all vectors

00:01:16.793 --> 00:01:20.705
to reflect the relative
magnitudes of all forces.

00:01:20.705 --> 00:01:22.528
Alright, so let's think about what are

00:01:22.528 --> 00:01:26.185
all the forces acting
on each of these blocks.

00:01:26.185 --> 00:01:27.925
Well for each of these blocks you're going

00:01:27.925 --> 00:01:29.912
to have the force of gravity, you're going

00:01:29.912 --> 00:01:33.128
to have the weight of the
blocks acting on them,

00:01:33.128 --> 00:01:38.128
so for example this first block m1,

00:01:38.234 --> 00:01:40.800
m1, and I'll draw it here first,

00:01:40.800 --> 00:01:44.629
what is the force of gravity going to be?

00:01:44.629 --> 00:01:46.096
The force of gravity is going to be

00:01:46.096 --> 00:01:50.311
its mass times the gravitational field.

00:01:50.311 --> 00:01:54.607
Now what is going to be the
force of gravity on block 2?

00:01:54.607 --> 00:01:56.244
Well it's going to be larger than that

00:01:56.244 --> 00:01:58.995
so let me just draw it like this,

00:01:58.995 --> 00:02:01.317
so the force of gravity is going to be

00:02:01.317 --> 00:02:04.045
m2 times g, how did I know
it was going to be larger?

00:02:04.045 --> 00:02:06.699
Well m2 has a larger mass and we are

00:02:06.699 --> 00:02:09.119
in the same gravitational field.

00:02:09.119 --> 00:02:12.023
Now we're not done there, no not done yet

00:02:12.023 --> 00:02:15.088
because now we also have the upward

00:02:15.088 --> 00:02:18.918
pulling force of the tension in the string

00:02:18.918 --> 00:02:20.543
and we could think
about what the magnitude

00:02:20.543 --> 00:02:22.285
of that, we know that the, we know that

00:02:22.285 --> 00:02:24.282
the tension is going to be pulling upwards

00:02:24.282 --> 00:02:26.226
on both of the blocks
but let's think about

00:02:26.226 --> 00:02:28.067
what its magnitude is going to be.

00:02:28.067 --> 00:02:30.459
In order for block 1
to accelerate upwards,

00:02:30.459 --> 00:02:33.198
which is in our intuition
as to what would happen,

00:02:33.198 --> 00:02:35.625
the tension, the force of the tension

00:02:35.625 --> 00:02:38.299
has to be larger, the
magnitude of the tension

00:02:38.299 --> 00:02:41.708
has to be larger than the
magnitude of the weight.

00:02:41.708 --> 00:02:45.481
Now in order for block 2
to accelerate downwards

00:02:45.481 --> 00:02:48.024
the magnitude of the
tension has to be less than

00:02:48.024 --> 00:02:50.723
the downward force of gravity, the upward

00:02:50.723 --> 00:02:52.704
force of tension has to be less than

00:02:52.704 --> 00:02:54.502
the downward force of gravity.

00:02:54.502 --> 00:02:56.279
So the magnitude of the tension

00:02:56.279 --> 00:02:58.788
is going to be inbetween the magnitudes

00:02:58.788 --> 00:03:02.918
of these two weights, so let me draw that.

00:03:02.918 --> 00:03:05.126
So the magnitude of the
tension is going to be

00:03:05.126 --> 00:03:09.398
larger than m1g but smaller than m2g,

00:03:09.398 --> 00:03:13.078
so maybe like that, so
that is tension right there

00:03:13.078 --> 00:03:17.966
and, whoops, and you're going to have

00:03:17.966 --> 00:03:20.618
on this side you're going to have the same

00:03:20.618 --> 00:03:24.469
magnitude of your tension pulling upwards

00:03:24.469 --> 00:03:26.453
but it's now less than the weight,

00:03:26.453 --> 00:03:29.135
which means that the block is
going to accelerate downwards

00:03:29.135 --> 00:03:31.075
and we know that these two tensions,

00:03:31.075 --> 00:03:32.931
the magnitudes of these tension vectors

00:03:32.931 --> 00:03:34.592
are going to be the same because of

00:03:34.592 --> 00:03:36.368
the magnitude of the tension throughout

00:03:36.368 --> 00:03:39.166
this entire string is
going to be the same.

00:03:39.166 --> 00:03:41.686
When you think about
tension, this pulling force,

00:03:41.686 --> 00:03:43.272
you can think about what's happening at an

00:03:43.272 --> 00:03:46.905
atomic or a molecular level
is these are the, you know

00:03:46.905 --> 00:03:48.904
the covalent bonds pulling on each other

00:03:48.904 --> 00:03:51.945
at an atomic level
throughout the entire string

00:03:51.945 --> 00:03:54.186
and when we look at it on a macro level

00:03:54.186 --> 00:03:55.997
we view that as tension.

00:03:55.997 --> 00:03:57.681
So there you have it, I've drawn

00:03:57.681 --> 00:03:59.063
the forces on them but I haven't

00:03:59.063 --> 00:04:00.224
drawn them in the right place,

00:04:00.224 --> 00:04:01.698
I need to draw them on this,

00:04:01.698 --> 00:04:03.626
I need to draw them right over here.

00:04:03.626 --> 00:04:04.623
So let me draw that, I can actually

00:04:04.623 --> 00:04:06.202
draw a little bit more precisely

00:04:06.202 --> 00:04:09.465
because they gave us these lines.

00:04:09.465 --> 00:04:14.260
So on block 1 I have the weight

00:04:14.260 --> 00:04:18.758
so that is m1g,

00:04:18.758 --> 00:04:20.778
I also have the tension,

00:04:20.778 --> 00:04:23.536
I'll make that two of these lines tall,

00:04:23.536 --> 00:04:26.706
so I also have the tension.

00:04:26.706 --> 00:04:29.062
Now block 2 I have the same tension

00:04:29.062 --> 00:04:31.293
or same magnitude of tension I should say,

00:04:31.293 --> 00:04:35.982
now it's also pulling upwards, so tension,

00:04:35.982 --> 00:04:37.816
and I have its weight, which is going

00:04:37.816 --> 00:04:39.851
to be larger than the tension,

00:04:39.851 --> 00:04:44.422
so its weight, I'll make
it three of these lines.

00:04:44.422 --> 00:04:46.721
The way I've drawn it m2 would have

00:04:46.721 --> 00:04:49.043
to be three times, m2 would have to be

00:04:49.043 --> 00:04:51.386
three times larger than
m1 the way I've drawn it.

00:04:51.386 --> 00:04:53.881
They don't tell us that, they
tell us that m2 is larger

00:04:53.881 --> 00:04:55.966
so this seems to be right.

00:04:55.966 --> 00:04:58.018
And we just want to get our intuition here

00:04:58.018 --> 00:05:01.141
since our tension, our upward force

00:05:01.141 --> 00:05:02.279
is larger than our downward force

00:05:02.279 --> 00:05:04.043
you're going to have a net upward force,

00:05:04.043 --> 00:05:06.435
which is going to accelerate block 1 up

00:05:06.435 --> 00:05:07.956
and here you're going to
have a net downward force,

00:05:07.956 --> 00:05:10.557
which is going to accelerate block 2 down,

00:05:10.557 --> 00:05:12.925
which is in line with our intuition

00:05:12.925 --> 00:05:17.088
because block 2 weighs more than block 1.


The discovery of the double helix structure of DNA

WEBVTT
Kind: captions
Language: en

00:00:00.120 --> 00:00:02.849
- [Voiceover] In 1865,
Mendel, often considered

00:00:02.849 --> 00:00:05.228
the father of modern genetics, comes up

00:00:05.228 --> 00:00:06.866
with a structured way of thinking about

00:00:06.866 --> 00:00:10.139
these inheritable factors,
which we now call "genes."

00:00:10.139 --> 00:00:12.310
And then as we go into the early 1900's,

00:00:12.310 --> 00:00:14.040
his work was rediscovered, and people

00:00:14.040 --> 00:00:16.745
started to say, "Okay, we see how some

00:00:16.745 --> 00:00:18.707
"of these traits get passed on in these

00:00:18.707 --> 00:00:20.386
"somewhat predictable ways, we can put

00:00:20.386 --> 00:00:22.058
"some structure around it, but what is

00:00:22.058 --> 00:00:25.318
"the actual biological mechanism for that?

00:00:25.318 --> 00:00:28.468
"How are these traits
encoded at a cellular,

00:00:28.468 --> 00:00:30.268
"or at a molecular level?"

00:00:30.268 --> 00:00:32.996
And so, in 1902, and we talked about this

00:00:32.996 --> 00:00:35.713
in a previous video,
Boveri and Sutton come up

00:00:35.713 --> 00:00:37.537
with the Chromosome Theory, based on

00:00:37.537 --> 00:00:40.334
seeing how chromosomes separate and pair

00:00:40.334 --> 00:00:42.245
during cell division, and saying,

00:00:42.245 --> 00:00:44.881
"Hey, those seem to map up quite well

00:00:44.881 --> 00:00:48.445
"to what Mendel described
by these heritable factors."

00:00:48.445 --> 00:00:50.744
Then we start having a lot
more evidence for this.

00:00:50.744 --> 00:00:54.924
Morgan is able to show that a mutant

00:00:54.924 --> 00:00:58.965
eye color trait seems to be passed on

00:00:58.965 --> 00:01:01.473
in a way that shows that it is on

00:01:01.473 --> 00:01:05.105
the X sex chromosome, and he and his team

00:01:05.105 --> 00:01:07.311
start doing a lot more work,
especially with fruit flies,

00:01:07.311 --> 00:01:10.575
to show that, "Hey,
chromosomes are the basis

00:01:10.575 --> 00:01:12.926
"for where these heritable factors are."

00:01:12.926 --> 00:01:14.331
But then even within the chromosomes,

00:01:14.331 --> 00:01:15.684
people weren't sure, chromosomes were made

00:01:15.684 --> 00:01:17.949
up of protein, made up of DNA, what was

00:01:17.949 --> 00:01:20.004
the molecule or the set
of molecules that actually

00:01:20.004 --> 00:01:24.148
encoded for these heritable traits?

00:01:24.148 --> 00:01:26.679
And at first, most of the weight was on

00:01:27.599 --> 00:01:30.879
the protein side, because
proteins were these

00:01:30.879 --> 00:01:34.582
complex molecules that
had all of this variety

00:01:34.582 --> 00:01:37.346
that seemed that it could code

00:01:37.346 --> 00:01:41.246
for these heritable traits, while DNA,

00:01:41.246 --> 00:01:43.465
at least early on, seemed like a kind of

00:01:43.465 --> 00:01:47.414
boring molecule, people assumed

00:01:47.414 --> 00:01:50.184
that there wasn't a lot
of diversity in DNA.

00:01:50.184 --> 00:01:51.612
They assumed that even if you go from

00:01:51.612 --> 00:01:54.272
one species to another
that the DNA molecule

00:01:54.272 --> 00:01:56.105
was fundamentally the same.

00:01:56.105 --> 00:01:58.671
So early on, people
actually were on the side

00:01:58.671 --> 00:02:00.448
more of the proteins.

00:02:00.448 --> 00:02:03.827
But then more and more evidence came

00:02:03.827 --> 00:02:06.744
on DNA's side, you had
Griffith's experiment,

00:02:06.744 --> 00:02:08.301
where he was able to
show, "Hey, I could take

00:02:08.301 --> 00:02:11.284
"this heat-killed
bacteria, but if I mix it

00:02:11.284 --> 00:02:13.304
"with some other living
bacteria that somehow

00:02:13.304 --> 00:02:15.162
"there's some transformation principle

00:02:15.162 --> 00:02:18.729
"that transforms the
living bacteria into the

00:02:18.729 --> 00:02:21.114
"type of species that I had heat-killed."

00:02:21.114 --> 00:02:23.795
And you go to 1944 and Avery, McCarty,

00:02:23.795 --> 00:02:25.896
and MacLeod are able to
show some pretty good

00:02:25.896 --> 00:02:28.191
evidence that the actual principle,

00:02:28.191 --> 00:02:32.127
the thing that was left in
that heat-killed bacteria,

00:02:32.127 --> 00:02:34.735
was probably DNA.

00:02:36.685 --> 00:02:38.463
And then we get even
more conclusive evidence

00:02:38.463 --> 00:02:40.041
with the experiments of Hershey and Chase

00:02:40.041 --> 00:02:41.504
and we have a whole video on this.

00:02:41.504 --> 00:02:43.304
Where they say, "Hey what is it that

00:02:43.304 --> 00:02:46.288
"viruses inject into bacteria to hijack

00:02:46.288 --> 00:02:49.481
"their genetic system?"

00:02:49.481 --> 00:02:51.117
And they say, "Hey, it's not proteins!

00:02:51.117 --> 00:02:52.626
"It is DNA that does this."

00:02:52.626 --> 00:02:55.007
So they provide much more conclusive

00:02:55.007 --> 00:02:57.120
evidence on the side of DNA.

00:02:57.120 --> 00:02:59.779
But even at that point, we as a community,

00:02:59.779 --> 00:03:01.207
as a civilization, still didn't know what

00:03:01.207 --> 00:03:03.661
the actual structure of DNA was.

00:03:03.661 --> 00:03:06.136
We also did not know,
how did that structure

00:03:06.136 --> 00:03:09.026
actually code for all of
these heritable factors?

00:03:09.026 --> 00:03:11.987
And the work culminates
with Watson and Crick,

00:03:11.987 --> 00:03:13.565
but it was dependent on all of the people

00:03:13.565 --> 00:03:15.192
I mentioned, and more.

00:03:15.192 --> 00:03:17.164
And one person who
should get special credit

00:03:17.164 --> 00:03:19.126
for, one, getting a
little bit more evidence

00:03:19.126 --> 00:03:21.413
on the side of DNA and helping Watson

00:03:21.413 --> 00:03:23.307
and Crick, actually
there's several people.

00:03:23.307 --> 00:03:25.268
But, in particular, Chargaff,

00:03:25.268 --> 00:03:28.809
and Rosalind Franklin,
and Rosalind Franklin

00:03:28.809 --> 00:03:29.993
in particular probably does not get

00:03:29.993 --> 00:03:31.684
as much credit as she deserves.

00:03:31.684 --> 00:03:33.204
Chargaff's the one that showed,

00:03:33.204 --> 00:03:35.050
DNA actually is more interesting than

00:03:35.050 --> 00:03:36.664
people appreciated.

00:03:36.664 --> 00:03:41.448
He noticed that the frequencies

00:03:41.448 --> 00:03:44.632
of the nitrogenous bases of adenine,

00:03:44.632 --> 00:03:47.743
guanine, cytosine, and thymine

00:03:47.743 --> 00:03:51.639
in DNA varies across species.

00:03:56.763 --> 00:03:58.247
And, something that's somehow coding

00:03:58.247 --> 00:04:00.173
for what makes a species a species,

00:04:00.173 --> 00:04:01.926
well, it would have to vary across species

00:04:01.926 --> 00:04:03.656
so that makes DNA interesting.

00:04:03.656 --> 00:04:04.818
And then the other thing that he noticed,

00:04:04.818 --> 00:04:07.569
and this was key for
Watson and Crick's work,

00:04:07.569 --> 00:04:11.098
is that the frequency of guanine is equal

00:04:11.098 --> 00:04:13.432
to the frequency of cytosine in DNA,

00:04:13.432 --> 00:04:15.673
and the frequency of adenine is equal

00:04:15.673 --> 00:04:18.274
to the frequency of thymine in DNA.

00:04:18.274 --> 00:04:20.374
And so it's a clue that these somehow

00:04:20.374 --> 00:04:22.801
are associated with
each other, they somehow

00:04:22.801 --> 00:04:24.740
pair with each other.

00:04:24.740 --> 00:04:27.120
And so we get to the early '50's.

00:04:27.120 --> 00:04:28.583
We had all of this evidence that DNA

00:04:28.583 --> 00:04:30.638
is the molecular basis, you have Chargaff

00:04:30.638 --> 00:04:33.586
with his rules called Chargaff's Rules,

00:04:33.586 --> 00:04:35.978
and then you have Rosalind Franklin,

00:04:40.218 --> 00:04:42.553
and she's imaging diffraction patterns

00:04:42.553 --> 00:04:45.876
from X-rays beamed into crystals of DNA.

00:04:45.876 --> 00:04:47.988
So what I mean by crystal of DNA,

00:04:47.988 --> 00:04:50.450
a crystal is taking a bunch of molecules

00:04:50.450 --> 00:04:53.515
and arranging them in a regular pattern.

00:04:53.515 --> 00:04:56.812
So a crystal of DNA,
that's one DNA molecule,

00:04:56.812 --> 00:04:58.972
then you have another
DNA molecule, and then

00:04:58.972 --> 00:05:01.375
you have another DNA molecule,

00:05:01.375 --> 00:05:02.954
and then you beam X-rays at them,

00:05:02.954 --> 00:05:06.078
and X-rays are key because the wavelength

00:05:06.078 --> 00:05:08.835
of an X-ray is small enough to capture

00:05:08.835 --> 00:05:11.354
the features at an atomic level.

00:05:11.354 --> 00:05:14.223
So you beam X-rays and
then the X-rays diffract.

00:05:14.223 --> 00:05:18.647
And then you capture the
pattern of that diffraction.

00:05:18.647 --> 00:05:20.380
And then depending on the structures

00:05:20.380 --> 00:05:21.681
in the actual molecules you'll have

00:05:21.681 --> 00:05:23.620
different diffraction patterns.

00:05:23.620 --> 00:05:26.220
And Franklin's famous diffraction pattern

00:05:26.220 --> 00:05:27.847
is shown right over here, and when she

00:05:27.847 --> 00:05:29.680
immediately saw this, it had some

00:05:29.680 --> 00:05:34.022
of the telltale cues
for a helical structure.

00:05:34.022 --> 00:05:36.054
Now, I wouldn't read too much into this

00:05:36.054 --> 00:05:39.339
if you're not an expert reader of X-ray

00:05:39.339 --> 00:05:43.799
diffraction patterns,
this isn't a direct image

00:05:43.799 --> 00:05:47.040
of a DNA molecule, but they knew,

00:05:47.040 --> 00:05:48.538
she already knew and in fact people

00:05:48.538 --> 00:05:50.198
in this community already knew that

00:05:50.198 --> 00:05:54.506
this X pattern was a telltale sign

00:05:56.009 --> 00:06:00.317
for a helical structure of some kind,

00:06:00.317 --> 00:06:01.432
and then they were also able to look

00:06:01.432 --> 00:06:04.090
at the other clues here to think about,

00:06:04.090 --> 00:06:06.801
"What's the spacing between
different molecules?"

00:06:06.801 --> 00:06:08.403
And even the spacing between the different

00:06:08.403 --> 00:06:11.015
turns of the helix structure.

00:06:11.015 --> 00:06:13.650
Now once again, this diffraction pattern

00:06:13.650 --> 00:06:15.136
is not a direct image.

00:06:18.636 --> 00:06:20.223
It's a very well-develped expertise

00:06:20.223 --> 00:06:23.125
to backwards map how things will diffract

00:06:23.125 --> 00:06:25.563
into the thing that actually
caused the diffraction.

00:06:25.563 --> 00:06:27.781
And they would take it from multiple

00:06:27.781 --> 00:06:29.278
different angles to get
a better understanding

00:06:29.278 --> 00:06:31.027
of it and actually
today, you have computers

00:06:31.027 --> 00:06:33.058
doing this that could
take a diffraction pattern

00:06:33.058 --> 00:06:36.425
and start to construct what the electron

00:06:36.425 --> 00:06:38.921
clouds of what the actual
molecule looks like.

00:06:38.921 --> 00:06:40.918
So Franklin, this was painstaking work,

00:06:40.918 --> 00:06:43.600
and she already had a sense,

00:06:43.600 --> 00:06:45.097
she knew it was a helical structure but

00:06:45.097 --> 00:06:47.280
she was waiting to get a little bit more

00:06:47.280 --> 00:06:49.300
evidence before she published her work.

00:06:49.300 --> 00:06:51.425
Now at the same time, you have Watson

00:06:51.425 --> 00:06:54.885
and Crick here, who were
trying to solve the structure.

00:06:54.885 --> 00:06:57.439
And they got a hold of Franklin's work

00:06:57.439 --> 00:06:59.656
with the help of Maurice Wilkins here,

00:06:59.656 --> 00:07:01.782
who Franklin worked with.

00:07:01.782 --> 00:07:04.202
And they were able to establish

00:07:04.202 --> 00:07:07.193
that it wasn't a single helix,
but it was a double helix.

00:07:07.193 --> 00:07:09.202
And you actually had these base pairs

00:07:09.202 --> 00:07:11.175
forming the rungs of the double helix,

00:07:11.175 --> 00:07:12.696
and that was really interesting because

00:07:12.696 --> 00:07:15.622
that showed how DNA
could replicate itself,

00:07:15.622 --> 00:07:18.257
how it could contain actual information.

00:07:18.257 --> 00:07:19.964
And we go into much much more depth

00:07:19.964 --> 00:07:21.694
in two future videos.

00:07:21.694 --> 00:07:23.795
Now the sad part about this story is,

00:07:23.795 --> 00:07:27.255
Wilkins, Watson, and Crick went on to win

00:07:27.255 --> 00:07:30.634
a Nobel prize, Franklin unfortunately died

00:07:30.634 --> 00:07:32.793
very young and you're
not allowed to receive

00:07:32.793 --> 00:07:35.498
a Nobel prize if you've passed away.

00:07:35.498 --> 00:07:37.578
So she's very deserving of it.

00:07:37.578 --> 00:07:39.673
This work, which a lot of people consider

00:07:39.673 --> 00:07:41.461
to be one of the biggest discoveries

00:07:41.461 --> 00:07:44.932
in science, was based on what she did.

00:07:44.932 --> 00:07:47.591
Arguably, had Watson and Crick not had

00:07:47.591 --> 00:07:49.100
access to her work, they would not have

00:07:49.100 --> 00:07:51.701
been able to figure it
out, and if she'd just

00:07:51.701 --> 00:07:52.757
stuck to what she was doing without

00:07:52.757 --> 00:07:54.116
other people having accessed her work,

00:07:54.116 --> 00:07:56.119
she might have been
able to get to that same

00:07:56.119 --> 00:07:58.011
conclusion, so she is
one of the people who,

00:07:58.011 --> 00:08:00.693
sometimes, the history
of science overlooks.

00:08:00.693 --> 00:08:02.992
But this isn't to not give credit to

00:08:02.992 --> 00:08:04.675
Watson and Crick either, there were still

00:08:04.675 --> 00:08:06.916
a lot of very powerful intuitive leaps

00:08:06.916 --> 00:08:09.192
that they had to make to come up with this

00:08:09.192 --> 00:08:11.850
double helix structure, this anti-parallel

00:08:11.850 --> 00:08:13.000
double helix structure where they go

00:08:13.000 --> 00:08:15.856
in opposite directions, but they bridge

00:08:15.856 --> 00:08:19.211
with these nitrogenous bases
pairing with each other.

00:08:19.211 --> 00:08:22.311
And this is a big, big, big, big deal.

00:08:22.311 --> 00:08:25.016
Throughout most of human history, we knew

00:08:25.016 --> 00:08:26.734
that traits were passed on but traits

00:08:26.734 --> 00:08:28.673
seemed like this magical mystical thing.

00:08:30.113 --> 00:08:31.902
"I know my laugh is like my dad's,

00:08:31.902 --> 00:08:35.640
"but how is that actually
encoded in my DNA?"

00:08:35.640 --> 00:08:37.823
And now, we're able to see that a lot

00:08:37.823 --> 00:08:41.051
of what we consider
about ourselves to be us,

00:08:41.051 --> 00:08:43.407
is encoded in these molecules and encoded

00:08:43.407 --> 00:08:46.008
in these base pairs, so it's beautiful,

00:08:46.008 --> 00:08:49.387
it's incredible, it's
shedding light on one

00:08:49.387 --> 00:08:52.127
of the biggest mysteries
of what makes humans,

00:08:52.127 --> 00:08:55.151
actually all life, life.


Hershey and Chase conclusively show DNA genetic material

WEBVTT
Kind: captions
Language: en

00:00:00.199 --> 00:00:01.347
- [Voiceover] In the last video we began

00:00:01.347 --> 00:00:02.478
to see some pretty good evidence

00:00:02.478 --> 00:00:06.757
that DNA was the molecular
basis for inheritance

00:00:06.757 --> 00:00:09.039
and we saw that from the work of Avery,

00:00:09.039 --> 00:00:12.302
McCarthy and McLead where
they tried to identify

00:00:12.302 --> 00:00:15.731
whether it was DNA or proteins that acted

00:00:15.731 --> 00:00:17.985
as a transformation principle
in Griffith's experiments

00:00:17.985 --> 00:00:20.568
and I encourage you to watch that video

00:00:20.568 --> 00:00:22.981
if all of this sounds unfamiliar.

00:00:22.981 --> 00:00:25.622
But even their work in 1944

00:00:25.622 --> 00:00:28.384
was not viewed as conclusive evidence.

00:00:28.384 --> 00:00:29.984
It was viewed as strong evidence,

00:00:29.984 --> 00:00:32.086
but not conclusive evidence because,

00:00:32.086 --> 00:00:33.044
remember how they did it,

00:00:33.044 --> 00:00:35.723
they took the heat killed smooth strain,

00:00:35.723 --> 00:00:36.767
the smooth strain you might remember

00:00:36.767 --> 00:00:39.173
from Griffith's experiment
was the virulent one.

00:00:39.173 --> 00:00:40.205
The heat killed it.

00:00:40.205 --> 00:00:41.865
When you heat kill it in injected amounts,

00:00:41.865 --> 00:00:43.182
it didn't do anything to the mouse,

00:00:43.182 --> 00:00:47.328
but if you took the heat
killed smooth strain

00:00:47.328 --> 00:00:50.208
and put it with the rough strain,

00:00:50.208 --> 00:00:53.091
it somehow transformed the rough strain

00:00:53.091 --> 00:00:55.002
in to the smooth strain,

00:00:55.002 --> 00:00:56.519
in to the virulent strain and so

00:00:56.519 --> 00:00:58.208
they took the heat killed smooth strain

00:00:58.208 --> 00:01:00.451
and they took out its different components

00:01:00.451 --> 00:01:01.752
and they eventually were able to isolate

00:01:01.752 --> 00:01:05.961
one that was able to
transform the rough strain

00:01:05.961 --> 00:01:08.393
in to the smooth strain by itself

00:01:08.393 --> 00:01:10.512
and then they applied all
sorts of chemical tests to it

00:01:10.512 --> 00:01:11.960
and said, "Hey, there's
pretty good evidence

00:01:11.960 --> 00:01:14.158
"that this is DNA,"

00:01:14.158 --> 00:01:15.931
but it wasn't conclusive because, well,

00:01:15.931 --> 00:01:17.118
maybe they didn't purify it properly

00:01:17.118 --> 00:01:18.929
or maybe there was still
a little bit of protein.

00:01:18.929 --> 00:01:19.962
Maybe it was mostly DNA, but maybe it was

00:01:19.962 --> 00:01:22.374
a little bit of protein
that was still left there

00:01:22.374 --> 00:01:24.911
that actually did the transformation.

00:01:24.911 --> 00:01:27.064
So the scientific community,

00:01:27.064 --> 00:01:28.359
they weren't just saying,
"Hey, that looks pretty good,

00:01:28.359 --> 00:01:29.373
"Let's move on, let's just assume."

00:01:29.373 --> 00:01:30.339
They wanted to continue to test it

00:01:30.339 --> 00:01:33.178
and especially test it in different ways.

00:01:33.178 --> 00:01:35.609
And, the conclusive evidence didn't come

00:01:35.609 --> 00:01:39.106
until a few years later, until 1952

00:01:39.106 --> 00:01:42.610
when Alfred Hershey and Martha Chase

00:01:42.610 --> 00:01:45.921
decided to study T2 bacterio phage.

00:01:45.921 --> 00:01:48.944
Let me write this down.

00:01:48.944 --> 00:01:51.493
T2 bacterio phage,

00:01:51.493 --> 00:01:53.382
this is phage that infects bacteria.

00:01:53.382 --> 00:01:55.824
Bacterio

00:01:55.824 --> 00:01:58.417
phage.

00:01:58.417 --> 00:01:59.885
When you hear the word phage,

00:01:59.885 --> 00:02:01.855
we're referring to viruses.

00:02:01.855 --> 00:02:04.370
Now they knew that T2 bacterio phage

00:02:04.370 --> 00:02:09.370
was composed of proteins and DNA

00:02:10.612 --> 00:02:12.736
and they didn't, well, we now know,

00:02:12.736 --> 00:02:17.736
that it's a protein shell
and there's DNA inside,

00:02:19.126 --> 00:02:20.676
but they, from their
point of view, they said,

00:02:20.676 --> 00:02:23.520
"Okay, it's made up and if we try to

00:02:23.520 --> 00:02:26.096
"look at the stuff that
this virus is made of,

00:02:26.096 --> 00:02:28.335
"it's protein and DNA."

00:02:28.335 --> 00:02:32.741
So protein plus DNA,

00:02:32.741 --> 00:02:36.226
and they knew that this virus,

00:02:36.226 --> 00:02:37.535
when it infects bacteria,

00:02:37.535 --> 00:02:40.198
it injects something into that bacteria.

00:02:40.198 --> 00:02:42.814
So it injects something

00:02:45.224 --> 00:02:48.499
and that something is what

00:02:48.499 --> 00:02:53.040
hijacks that bacteria's
genetic information

00:02:53.040 --> 00:02:57.040
to start producing more
of the T2 bacterio phage.

00:02:57.040 --> 00:03:00.720
So they could identify the
something that gets injected.

00:03:00.720 --> 00:03:03.958
If they could figure out
if that something was

00:03:03.958 --> 00:03:06.779
either a protein or a virus,

00:03:06.779 --> 00:03:08.997
then they would have conclusively proven

00:03:08.997 --> 00:03:11.339
so sorry,

00:03:11.339 --> 00:03:14.037
if they could show that something
was not protein or virus,

00:03:14.037 --> 00:03:15.936
if it was protein or DNA,

00:03:15.936 --> 00:03:18.203
if they could show that it
was either protein or DNA,

00:03:18.203 --> 00:03:20.361
then they could show conclusively

00:03:20.361 --> 00:03:21.570
that it's either the protein or the DNA

00:03:21.570 --> 00:03:23.193
that forms the molecular basis

00:03:23.193 --> 00:03:25.155
and so they're actually quite sceptical

00:03:25.155 --> 00:03:27.651
of Avery, McCarthy and
MacLead's experiments.

00:03:27.651 --> 00:03:29.364
They actually, Hershey and Chase,

00:03:29.364 --> 00:03:32.371
actually thought that they were gonna show

00:03:32.371 --> 00:03:33.449
that it was the protein,

00:03:33.449 --> 00:03:34.536
and remember, this whole
time people were like,

00:03:34.536 --> 00:03:36.676
"Protein, we know it's
these complex molecules

00:03:36.676 --> 00:03:39.372
"that have these different shapes

00:03:39.372 --> 00:03:40.663
"and all these different amino acids.

00:03:40.663 --> 00:03:42.195
"It seems like that's
much more likely to encode

00:03:42.195 --> 00:03:45.255
"the complexity of genetic
information than DNA."

00:03:45.255 --> 00:03:47.438
They didn't have an
appreciation for the structure

00:03:47.438 --> 00:03:50.130
of DNA at this time.

00:03:50.130 --> 00:03:52.516
So they devised an
experiment to figure out

00:03:52.516 --> 00:03:55.644
what is that something

00:03:55.644 --> 00:03:56.994
that the T2 bacterio phage is infecting.

00:03:56.994 --> 00:03:59.983
Is that something protein?

00:03:59.983 --> 00:04:02.368
Is it protein

00:04:02.368 --> 00:04:04.835
or

00:04:04.835 --> 00:04:06.659
DNA?

00:04:06.659 --> 00:04:07.898
So this is the question.

00:04:07.898 --> 00:04:09.054
So what they do is

00:04:09.054 --> 00:04:11.984
they take two batches or
they developed two batches

00:04:11.984 --> 00:04:14.149
of T2 bacterio phage.

00:04:14.149 --> 00:04:16.956
One batch of the T2 bacterio phage

00:04:16.956 --> 00:04:21.948
they do it in the presence
of radioactive phosphorus,

00:04:21.948 --> 00:04:24.778
phosphorus 32.

00:04:24.778 --> 00:04:27.875
In the other batch, I should say

00:04:27.875 --> 00:04:29.754
they grow that T2 bacterio phage

00:04:29.754 --> 00:04:32.536
in the process of another
radioactive isotope,

00:04:32.536 --> 00:04:34.560
but this time it is of sulfur.

00:04:34.560 --> 00:04:37.908
This is sulfur 35.

00:04:37.908 --> 00:04:39.754
So why are they doing that?

00:04:39.754 --> 00:04:42.759
Well phosphorus is found in DNA.

00:04:42.759 --> 00:04:45.130
So in this first batch,

00:04:45.130 --> 00:04:47.227
the radioactive marker, you could say,

00:04:47.227 --> 00:04:49.862
is going to incorporate
itself into the DNA.

00:04:49.862 --> 00:04:52.024
In the second batch, sulfur is found

00:04:52.024 --> 00:04:54.523
in the protein and not in the DNA

00:04:54.523 --> 00:04:58.026
and so this would actually
tag the protein parts.

00:04:58.026 --> 00:05:01.163
And if you're wondering, well,

00:05:01.163 --> 00:05:04.220
how do you develop these
radioactive batches,

00:05:04.220 --> 00:05:05.391
well, you let the viruses hijack cells

00:05:05.391 --> 00:05:06.659
in a medium that has either
the radioactive sulfur

00:05:06.659 --> 00:05:10.271
or the radioactive phosphorus
and as they reproduce,

00:05:10.271 --> 00:05:13.060
they are going to incorporate
that radioactive material

00:05:13.060 --> 00:05:17.910
into either the protein or
the DNA of the new viruses

00:05:17.910 --> 00:05:19.210
that get produced.

00:05:19.210 --> 00:05:22.882
So anyway, they were able to produce some

00:05:22.882 --> 00:05:24.361
of the T2 bacterio phage in the presence

00:05:24.361 --> 00:05:26.103
of the radioactive phosphorus

00:05:26.103 --> 00:05:28.550
and they knew that way that the DNA

00:05:28.550 --> 00:05:30.872
would get that radioactive material in it

00:05:30.872 --> 00:05:32.576
and then with the radioactive sulfur

00:05:32.576 --> 00:05:34.258
they said the protein would
have that radioactive sulfur.

00:05:34.258 --> 00:05:35.905
And then for each of those batches,

00:05:35.905 --> 00:05:40.032
they then infected
bacterio phage with them

00:05:40.032 --> 00:05:43.337
and they said, okay, they're
going to inject something

00:05:43.337 --> 00:05:44.445
in to the bacterio phage,
and to figure out what

00:05:44.445 --> 00:05:46.911
that something is that was
injected in to the bacterio phage

00:05:46.911 --> 00:05:50.285
they take the products in
either of the two scenarios,

00:05:50.285 --> 00:05:52.941
they first blend 'em up so that all

00:05:52.941 --> 00:05:55.862
of the stuff that's left outside

00:05:55.862 --> 00:06:00.441
gets taken off of the
surface of the bacteria cells

00:06:00.441 --> 00:06:02.828
and then they stick it in to a centrifuge

00:06:02.828 --> 00:06:04.153
and the centrifuge is, you can imagine,

00:06:04.153 --> 00:06:05.743
it's kind of just a big spinning machine.

00:06:05.743 --> 00:06:08.228
If you were to take a test
tube and take it sideways,

00:06:08.228 --> 00:06:10.518
one way to think about it,
put it sideways like this.

00:06:10.518 --> 00:06:13.056
Put maybe a stopper in it so nothing leaks

00:06:13.056 --> 00:06:15.828
and then you spin it
around really, really,

00:06:15.828 --> 00:06:17.131
really, really fast,

00:06:17.131 --> 00:06:18.600
what you're going to find,

00:06:18.600 --> 00:06:20.342
you can actually generate
significant g forces

00:06:20.342 --> 00:06:22.881
and so the heavier stuff
is going to gravitate

00:06:22.881 --> 00:06:24.724
to the bottom of the
test tube or to the right

00:06:24.724 --> 00:06:26.342
when it is on its side,

00:06:26.342 --> 00:06:27.942
and the lighter stuff
is going to gravitate

00:06:27.942 --> 00:06:30.455
to the left.

00:06:30.455 --> 00:06:33.264
And, it turns out that the bacteria,

00:06:33.264 --> 00:06:34.531
the actual bacterial cells,

00:06:34.531 --> 00:06:36.324
those are heavier so the bacterial cells

00:06:36.324 --> 00:06:39.180
are going to go towards
the bottom of the test tube

00:06:39.180 --> 00:06:40.546
and they're gonna form a material

00:06:40.546 --> 00:06:43.502
that we call the pellet

00:06:43.502 --> 00:06:45.533
and then all of the other stuff,

00:06:45.533 --> 00:06:49.369
all of the fluid and
the leftover phage parts

00:06:49.369 --> 00:06:52.275
those are going to go up to the top

00:06:52.275 --> 00:06:54.412
of the test tube and we
call that the supernatent.

00:06:54.412 --> 00:06:57.405
I always have trouble pronouncing that.

00:06:57.405 --> 00:06:58.304
Supernatent.

00:06:58.304 --> 00:07:00.565
And so they said, "Look,
if we look at the pellet,"

00:07:00.565 --> 00:07:04.070
which they knew had the
bacterial cells int here

00:07:04.070 --> 00:07:06.630
or you could even say the
remnants of the bacterial cells,

00:07:06.630 --> 00:07:08.665
"if the pellet here

00:07:08.665 --> 00:07:13.327
"contains phosphorus,
that means that the DNA,

00:07:13.327 --> 00:07:15.678
"our radioactive DNA or our tagged DNA

00:07:15.678 --> 00:07:17.946
"made it in to the bacteria,

00:07:17.946 --> 00:07:20.722
"but if it contains sulfur,
that means that the protein

00:07:20.722 --> 00:07:23.066
"made it in to the bacteria."

00:07:23.066 --> 00:07:25.912
And, what they found is

00:07:25.912 --> 00:07:28.987
they found that the radioactive

00:07:28.987 --> 00:07:33.056
phosphorus

00:07:33.056 --> 00:07:37.405
was in the pellet which
allowed them to conclude

00:07:37.405 --> 00:07:39.688
that, hey, it's the DNA from the virus

00:07:39.688 --> 00:07:41.693
that made it inside of the bacteria

00:07:41.693 --> 00:07:43.936
and not the protein

00:07:43.936 --> 00:07:46.245
and then they said, "Well, it must be!

00:07:46.245 --> 00:07:48.385
"Wow, the Avery, McCarthy
and Maclead were correct.

00:07:48.385 --> 00:07:52.548
"It's actually the DNA that is
this transformation principle

00:07:52.548 --> 00:07:57.401
"that can go in and hijack the genetic,

00:07:57.401 --> 00:07:58.656
"the machinery of the bacteria

00:07:58.656 --> 00:08:01.770
"to produce more of the actual virus,

00:08:01.770 --> 00:08:04.159
"so this is a really,
really, really big deal."

00:08:04.159 --> 00:08:05.591
Once again, we started with

00:08:05.591 --> 00:08:09.356
Mendel saying, "Hey, we have
these inheritable factors

00:08:09.356 --> 00:08:13.320
"and they seem to segregate
and sort in certain ways.

00:08:13.320 --> 00:08:16.272
"They seem to be discrete."

00:08:16.272 --> 00:08:17.636
Bover and Sutton said, "Hey,

00:08:17.636 --> 00:08:19.020
"chromosomes seem to kind of,

00:08:19.020 --> 00:08:20.554
"their behavior during meiosis

00:08:20.554 --> 00:08:21.621
"when cells split

00:08:21.621 --> 00:08:23.440
"seem to kind of match up to that."

00:08:23.440 --> 00:08:25.361
Morgan starts to provide some evidence.

00:08:25.361 --> 00:08:28.068
We have Griffith's
experiments with the mice

00:08:28.068 --> 00:08:31.046
and the bacteria and saying, "Hey, look,

00:08:31.046 --> 00:08:32.961
"there's some transformation principle."

00:08:32.961 --> 00:08:35.034
Avery, McCarthy and MacLeod say, "Hey,

00:08:35.034 --> 00:08:37.149
"looks like when we try to really purify

00:08:37.149 --> 00:08:38.839
"this transformation principle,

00:08:38.839 --> 00:08:41.311
"it seems like DNA is
what really matters."

00:08:41.311 --> 00:08:44.146
And then Hershey and Chase validate that

00:08:44.146 --> 00:08:47.794
even more conclusively.


Establishing DNA as transformation principle

WEBVTT
Kind: captions
Language: en

00:00:00.445 --> 00:00:02.495
- [Voiceover] So to
review how we got at least

00:00:02.495 --> 00:00:07.495
to this video, in 1865,
Mendel first shares his laws

00:00:07.536 --> 00:00:08.590
of inheritance.

00:00:08.590 --> 00:00:11.883
He observes that there are
these heritable factors,

00:00:11.883 --> 00:00:15.703
these discrete heritable factors
that would be passed down

00:00:15.703 --> 00:00:19.508
from parent to offspring
according to certain rules.

00:00:19.508 --> 00:00:21.781
And he came up with the
laws of inheritance,

00:00:21.781 --> 00:00:24.210
law of segregation, law
of independent assortment,

00:00:24.210 --> 00:00:25.540
law of dominance.

00:00:25.540 --> 00:00:28.390
But as we've said multiple
times, that work at the time

00:00:28.390 --> 00:00:31.208
that it was for shared
wasn't taken that seriously.

00:00:31.208 --> 00:00:33.246
In fact, a lot of people
didn't pay attention to it

00:00:33.246 --> 00:00:35.231
and it wasn't until the early 1900s

00:00:35.231 --> 00:00:37.376
that it was rediscovered.

00:00:37.376 --> 00:00:40.771
But even when it was first
rediscovered around 1900,

00:00:40.771 --> 00:00:44.350
people did not know
what the molecular basis

00:00:44.350 --> 00:00:47.772
for these heritable factors
that Mendel talked about,

00:00:47.772 --> 00:00:50.489
what the basis of these factors were.

00:00:50.489 --> 00:00:54.903
And in 1902, we have the
first really solid theory

00:00:54.903 --> 00:00:57.539
for what the molecular basis
for those inheritable factors

00:00:57.539 --> 00:00:59.211
actually could be.

00:00:59.211 --> 00:01:01.826
This is when Boveri and Sutton come up

00:01:01.826 --> 00:01:03.521
and they independently did their work,

00:01:03.521 --> 00:01:06.084
but they both came to
the same theory at around

00:01:06.084 --> 00:01:07.233
the same time.

00:01:07.233 --> 00:01:09.297
They came up with the chromosome theory,

00:01:09.297 --> 00:01:11.804
now called the Boveri-Sutton
chromosome theory.

00:01:11.804 --> 00:01:15.958
Their work was based on
observing how cells divide,

00:01:15.958 --> 00:01:19.197
especially meiosis, and in
seeing how these chromosomes

00:01:19.197 --> 00:01:23.611
seem to pair up then segregate
then independently assort

00:01:23.611 --> 00:01:25.542
and get passed on to their offspring.

00:01:25.542 --> 00:01:28.313
And they said hey, these
chromosomes, on a physical level,

00:01:28.313 --> 00:01:31.605
on a molecular level, seem
to be behaving in ways

00:01:31.605 --> 00:01:34.326
that are very similar
to the heritable factors

00:01:34.326 --> 00:01:35.660
that Mendel talked about.

00:01:35.660 --> 00:01:37.460
So it was a very strong theory.

00:01:37.460 --> 00:01:40.177
And then we get to 1911 where that theory

00:01:40.177 --> 00:01:43.288
gets some more evidence put behind it.

00:01:43.288 --> 00:01:45.114
Thomas Hunt Morgan, we talked about it,

00:01:45.114 --> 00:01:50.114
he used his fruit flies to
see how that mutant trait

00:01:50.531 --> 00:01:54.031
that would pass on from
one generation to another

00:01:54.031 --> 00:01:55.945
and the only plausible
explanation that he could

00:01:55.945 --> 00:01:58.792
come up with is that
it was being passed on,

00:01:58.792 --> 00:02:01.846
on the X sex chromosome.

00:02:01.846 --> 00:02:04.024
And him and his team continued
to do more and more work

00:02:04.024 --> 00:02:07.942
to establish that chromosomes
indeed seem to be the basis,

00:02:07.942 --> 00:02:11.079
the physical location for
these heritable factors

00:02:11.079 --> 00:02:13.951
that Mendel first talked about in 1865.

00:02:13.951 --> 00:02:16.119
But even Morgan and his team,

00:02:16.119 --> 00:02:17.479
when they looked at chromosomes,

00:02:17.479 --> 00:02:19.543
a lot of times now when
we think of chromosomes

00:02:19.543 --> 00:02:23.200
we think of chromosomes
as being made up of DNA,

00:02:23.200 --> 00:02:24.506
and that is true;

00:02:24.506 --> 00:02:26.648
but chromosomes are also
made up of other things,

00:02:26.648 --> 00:02:28.242
including proteins.

00:02:28.242 --> 00:02:30.566
And in the early days,
when people said hey,

00:02:30.566 --> 00:02:32.682
it looks like chromosomes
are really the basis

00:02:32.682 --> 00:02:34.970
or the location for
these heritable factors,

00:02:34.970 --> 00:02:35.936
for these genes.

00:02:35.936 --> 00:02:38.156
When people look at these
two different molecules,

00:02:38.156 --> 00:02:41.761
they said hey, it's probably
the proteins that are actually

00:02:41.761 --> 00:02:46.302
responsible for encoding the
information of inheritance.

00:02:46.302 --> 00:02:50.218
Proteins, people knew, were
these complex molecules

00:02:50.218 --> 00:02:53.378
that in some ways you could
say encoded information.

00:02:53.378 --> 00:02:55.209
Well, at the time, they thought that DNA

00:02:55.209 --> 00:02:57.279
were these kind of boring
molecules that surely

00:02:57.279 --> 00:03:00.991
this couldn't encode information.

00:03:00.991 --> 00:03:03.446
And so the first
evidence, strong evidence,

00:03:03.446 --> 00:03:08.446
that DNA is actually where
the genetic information

00:03:08.723 --> 00:03:12.641
is encoded doesn't happen
for several more decades.

00:03:12.641 --> 00:03:16.377
And we start along that path
with Griffith right over here,

00:03:16.377 --> 00:03:18.571
famous for Griffith's experiment,

00:03:18.571 --> 00:03:20.164
where he does something
really interesting.

00:03:20.164 --> 00:03:22.933
And he by himself, his experiments in 1920

00:03:22.933 --> 00:03:25.154
or that he publishes
in 1920 or he actually

00:03:25.154 --> 00:03:27.408
he conducts and publishes in 1928,

00:03:27.408 --> 00:03:30.074
they aren't responsible
in and of themselves

00:03:30.074 --> 00:03:34.123
for establishing DNA to be
the molecule that's actually

00:03:34.123 --> 00:03:37.362
the basis of inheritance,
but they start an interesting

00:03:37.362 --> 00:03:41.020
path of inquiry where
these gentlemen in 1944

00:03:41.020 --> 00:03:44.024
are finally able to establish that DNA

00:03:44.024 --> 00:03:48.386
is where these heritable factors

00:03:48.386 --> 00:03:51.233
are actually encoded.

00:03:51.233 --> 00:03:54.002
So what was Griffith's experiment?

00:03:54.002 --> 00:03:57.355
Well, he was studying

00:03:57.355 --> 00:04:00.267
strains of bacteria,

00:04:00.267 --> 00:04:03.715
and he saw that the same, the two variants

00:04:03.715 --> 00:04:07.555
on a certain strain or
two variants of bacteria,

00:04:07.555 --> 00:04:10.167
you had the rough strain
and the smooth strain,

00:04:10.167 --> 00:04:14.033
if he injected the rough
strain into a mouse,

00:04:14.033 --> 00:04:15.337
the mouse lived.

00:04:15.337 --> 00:04:18.160
If he injected the smooth
strain into a mouse,

00:04:18.160 --> 00:04:19.911
the mouse died.

00:04:19.911 --> 00:04:22.627
And it was because the
smooth strain had this

00:04:22.627 --> 00:04:25.736
protective coating on it
that made it harder to attack

00:04:25.736 --> 00:04:28.113
by the mouses immune system.

00:04:28.113 --> 00:04:30.281
So that by itself, well,
that's interesting,

00:04:30.281 --> 00:04:32.475
this is the virulent strain,

00:04:32.475 --> 00:04:34.983
this is the one that's actually
going to kill the mice.

00:04:34.983 --> 00:04:39.215
Now if he took this smooth
strain, the virulent strain

00:04:39.215 --> 00:04:43.636
and he heated up so those
bacteria were killed

00:04:43.636 --> 00:04:46.194
and then he injected those,
so this is the heat-killed

00:04:46.194 --> 00:04:49.670
smooth strain, if he injected
those into the mouse,

00:04:49.670 --> 00:04:53.406
the mouse still lived because
those bacteria were dead.

00:04:53.406 --> 00:04:56.775
But then he did something
very, very, very interesting.

00:04:56.775 --> 00:04:59.832
He took this, the
heat-killed smooth strain,

00:04:59.832 --> 00:05:02.052
he took some of that and
he took some of the live

00:05:02.052 --> 00:05:04.427
rough strain put together.

00:05:04.427 --> 00:05:06.284
Now common sense would
tell you is like okay,

00:05:06.284 --> 00:05:09.390
this blue stuff, that's not
going to kill the mouse,

00:05:09.390 --> 00:05:13.441
and this killed smooth strain,

00:05:13.441 --> 00:05:15.505
that's not going to kill the mouse either.

00:05:15.505 --> 00:05:18.326
So if mix it up, that
shouldn't kill the mouse,

00:05:18.326 --> 00:05:21.226
but it did kill the mouse,
which was fascinating.

00:05:21.226 --> 00:05:23.159
And so he came up with this theory

00:05:23.159 --> 00:05:24.907
of a transformation principle.

00:05:24.907 --> 00:05:28.540
Even though he killed
the smooth strain here,

00:05:28.540 --> 00:05:31.021
there must've been some type of materials,

00:05:31.021 --> 00:05:34.052
some type of molecule
that still got transferred

00:05:34.052 --> 00:05:37.683
from the dead bacteria
to the live bacteria

00:05:37.683 --> 00:05:40.478
and essentially transformed
the live bacteria

00:05:40.478 --> 00:05:45.478
into the smooth strain,
allowing them to kill the mouse.

00:05:45.702 --> 00:05:48.390
And so he came up with
this idea of some kind of

00:05:48.390 --> 00:05:50.926
transformation principle.

00:05:50.926 --> 00:05:53.800
And so you can imagine, and
look, it took some time,

00:05:53.800 --> 00:05:57.431
over 10 years, now almost two decades,

00:05:57.431 --> 00:06:00.328
Avery, McCarty and McLeod said hey,

00:06:00.328 --> 00:06:03.256
what is this transformation principle?

00:06:03.256 --> 00:06:06.208
Why don't we use Griffith's experiment

00:06:06.208 --> 00:06:09.183
and let's keep, instead
of just taking you know

00:06:09.183 --> 00:06:11.981
the whole heat-killed smooth strain,

00:06:11.981 --> 00:06:14.277
let's try to break it
up into its components

00:06:14.277 --> 00:06:16.289
and let's try to isolate
the different components

00:06:16.289 --> 00:06:18.668
and keep doing the
experiment until we have

00:06:18.668 --> 00:06:22.743
an isolated molecule or
an isolated component

00:06:22.743 --> 00:06:24.571
that seems to do the trick.

00:06:24.571 --> 00:06:27.941
So they were trying to isolate
the transformation principle.

00:06:27.941 --> 00:06:29.665
And they did just as what I described.

00:06:29.665 --> 00:06:32.304
They took the heat-killed smooth strain,

00:06:32.304 --> 00:06:35.540
they would try to separate the
different constituents out.

00:06:35.540 --> 00:06:38.388
You can separate them out physically,

00:06:38.388 --> 00:06:40.881
you could use certain
washes that would wash away

00:06:40.881 --> 00:06:42.056
certain components.

00:06:42.056 --> 00:06:45.174
You could use enzymes that would
destroy certain components.

00:06:45.174 --> 00:06:48.515
And eventually, and this
is very meticulous work,

00:06:48.515 --> 00:06:51.522
so you can imagine they take the stuff,

00:06:51.522 --> 00:06:54.500
the whole dead heat-killed smooth strain

00:06:54.500 --> 00:06:56.694
and they start to
separated it out into its

00:06:56.694 --> 00:06:58.245
various components.

00:06:58.245 --> 00:07:03.245
So that might be one
component right over there,

00:07:03.809 --> 00:07:07.542
this is another, let me do
it in these different colors,

00:07:07.542 --> 00:07:11.147
this is another component
right over there,

00:07:11.147 --> 00:07:14.205
this is another component
right over there.

00:07:14.205 --> 00:07:16.504
They're using different
chemical techniques to separate

00:07:16.504 --> 00:07:19.616
all of the constituents
that were in that original

00:07:19.616 --> 00:07:21.664
heat-killed smooth strain.

00:07:21.664 --> 00:07:24.773
And then instead of
running this last phase

00:07:24.773 --> 00:07:27.203
of the experiment with the
entire heat killed smooth strain,

00:07:27.203 --> 00:07:30.442
they do it with the rough
strain mixed with each

00:07:30.442 --> 00:07:32.817
of these components separately.

00:07:32.817 --> 00:07:34.854
And then they kept running the experiment

00:07:34.854 --> 00:07:35.937
and they would say, hey, look,

00:07:35.937 --> 00:07:38.233
when we have this
component right over here

00:07:38.233 --> 00:07:42.284
and we tried to run the
experiment, the mouse still lives.

00:07:42.284 --> 00:07:43.284
The mouse still lives.

00:07:43.284 --> 00:07:46.212
So this one did not
transform the rough strain.

00:07:46.212 --> 00:07:49.869
And maybe this one also did
not transform the rough strain.

00:07:49.869 --> 00:07:52.925
But then eventually, they
were able to isolate something

00:07:52.925 --> 00:07:55.039
that did transform the rough strain.

00:07:55.039 --> 00:07:57.784
So the mouse dies,

00:07:57.784 --> 00:08:00.159
and so it did transform the rough strain

00:08:00.159 --> 00:08:01.702
into the smooth strain.

00:08:01.702 --> 00:08:04.706
And so they took this material
and they start applying

00:08:04.706 --> 00:08:08.181
all sorts of test to it.

00:08:08.181 --> 00:08:12.543
They could look at the
molecular components of it.

00:08:12.543 --> 00:08:15.284
And when they looked at
the ratios of nitrogen

00:08:15.284 --> 00:08:18.159
and phosphorus, they said
hey, this seems to have

00:08:18.159 --> 00:08:21.398
ratios that are consistent with DNA,

00:08:21.398 --> 00:08:23.329
which is a molecule
they already knew about.

00:08:23.329 --> 00:08:25.785
And it was not ratios that
would've been consistent

00:08:25.785 --> 00:08:26.989
with proteins.

00:08:26.989 --> 00:08:28.539
They ran chemical tests and said hey,

00:08:28.539 --> 00:08:31.109
it doesn't look like there's
a lot of protein in this thing

00:08:31.109 --> 00:08:34.659
that we isolated, or even
RNA, which is another molecule

00:08:34.659 --> 00:08:35.654
that they new.

00:08:35.654 --> 00:08:38.428
Enzymes that would've
degraded proteins or RNA

00:08:38.428 --> 00:08:41.930
did not degrade this stuff, but
the enzyme that degraded DNA

00:08:41.930 --> 00:08:43.498
did degrade this stuff.

00:08:43.498 --> 00:08:47.034
And so they were able to come
up with the idea that DNA

00:08:47.034 --> 00:08:49.957
was the transformation principle.

00:08:49.957 --> 00:08:52.023
And this is a really,
really, really big deal.

00:08:52.023 --> 00:08:53.878
Think about this quest that
we've been going through

00:08:53.878 --> 00:08:57.117
for the better part of a hundred years.

00:08:57.117 --> 00:08:59.475
Inheritable factors, well,
where are they located?

00:08:59.475 --> 00:09:01.341
Hey, it looks like they're
on the chromosomes.

00:09:01.341 --> 00:09:03.143
We start having evidence that
they're on the chromosomes.

00:09:03.143 --> 00:09:06.510
But chromosomes are made
up of DNA and proteins,

00:09:06.510 --> 00:09:09.405
and it wasn't until the start
with Griffith's experiments

00:09:09.405 --> 00:09:11.956
and then Avery, McCarty and
McLeod come along and said hey,

00:09:11.956 --> 00:09:15.352
let's identify what was it
exactly about the heat-killed

00:09:15.352 --> 00:09:16.292
smooth strain

00:09:16.292 --> 00:09:18.552
What's the component in it
that actually transformed

00:09:18.552 --> 00:09:19.749
the other strain?

00:09:19.749 --> 00:09:20.889
And it was DNA.

00:09:20.889 --> 00:09:23.408
And what was fascinating
is when you mixed that DNA

00:09:26.064 --> 00:09:29.663
from the heat-killed smooth
strain with the rough strain,

00:09:29.663 --> 00:09:34.470
that DNA was able to mix in
with the DNA of the rough strain

00:09:34.470 --> 00:09:38.231
and allows it to start producing
these smooth protein coats

00:09:38.231 --> 00:09:40.948
that allowed it to be more virulent.

00:09:40.948 --> 00:09:44.037
So the mouse's immune system
couldn't attack it as well.

00:09:44.037 --> 00:09:45.664
So it's really fascinating
on a lot of levels.

00:09:45.664 --> 00:09:47.301
You know, the whole
takeaway from this one is

00:09:47.301 --> 00:09:50.070
how did we get to DNA
being the important part

00:09:50.070 --> 00:09:52.874
of the chromosomes, at
least in terms of encoding

00:09:52.874 --> 00:09:54.438
the actual genetic information,

00:09:54.438 --> 00:09:56.529
but it's also a cool way to think about

00:09:56.529 --> 00:09:59.680
just almost how magical DNA is,

00:09:59.680 --> 00:10:02.508
that if you mix it in,
if you mix it in the DNA

00:10:02.508 --> 00:10:07.380
of one strain with a live
version of another strain,

00:10:07.380 --> 00:10:10.540
you actually might be able
to transform that strain.

00:10:10.540 --> 00:10:15.136
In some ways, they were
doing very, very basic

00:10:15.136 --> 00:10:17.504
genetic engineering here.


How to read a document part 2

WEBVTT
Kind: captions
Language: en

00:00:00.540 --> 00:00:01.724
- [Voiceover] In our last video,

00:00:01.724 --> 00:00:03.930
we started looking at this speech by

00:00:03.930 --> 00:00:06.577
Franklin Delano Roosevelt which he gave

00:00:06.577 --> 00:00:10.687
at his innaguration in March of 1933.

00:00:10.687 --> 00:00:13.520
We took some time to just identify what

00:00:13.520 --> 00:00:15.052
was happening in this speech

00:00:15.052 --> 00:00:17.049
and also the context of this speech,

00:00:17.049 --> 00:00:19.371
coming at the height of
the Great Depression.

00:00:19.371 --> 00:00:23.017
- [Voiceover] Now we're gonna
dive deeper into our textual

00:00:23.017 --> 00:00:26.291
analysis and explore the soucre,

00:00:26.291 --> 00:00:28.172
figure out what is going on

00:00:28.172 --> 00:00:29.983
with Roosevelt's language
and what he's trying to say

00:00:29.983 --> 00:00:32.792
and what his biases are.

00:00:32.792 --> 00:00:35.997
- [Voiceover] Let's get a
little more into what else goes

00:00:35.997 --> 00:00:37.738
on in this speech, not just the very

00:00:37.738 --> 00:00:40.176
famous opening paragraph.

00:00:40.176 --> 00:00:44.170
We start here with
saying people are facing

00:00:44.170 --> 00:00:46.446
the grim problem of existence,

00:00:46.446 --> 00:00:49.580
and a foolish optimist can
deny the dark realities

00:00:49.580 --> 00:00:52.065
of the moment, and

00:00:52.065 --> 00:00:53.342
then what comes next?

00:00:53.342 --> 00:00:55.084
- [Voiceover] Let's hear
all this in context.

00:00:55.084 --> 00:00:58.961
Yet our distress comes from
no failure of substance.

00:00:58.961 --> 00:01:01.121
We are stricken by no plague of locusts,

00:01:01.121 --> 00:01:04.209
compared with the perils which
our forefathers conquered,

00:01:04.209 --> 00:01:05.533
because they believed and were not afraid,

00:01:05.533 --> 00:01:07.274
we still have much to be thankful for.

00:01:07.274 --> 00:01:08.946
Nature still offers her bounty and human

00:01:08.946 --> 00:01:10.525
efforts have multiplied.

00:01:10.525 --> 00:01:11.616
Plenty is at our doorstep,

00:01:11.616 --> 00:01:13.451
but a generous use of it languishes

00:01:13.451 --> 00:01:15.285
in the very sight of the supply.

00:01:15.285 --> 00:01:16.980
Primarily this is because the rulers

00:01:16.980 --> 00:01:19.186
of the exchange of
mankind's goods have failed

00:01:19.186 --> 00:01:21.949
through their own stubbornness
and their own incompetence.

00:01:21.949 --> 00:01:23.059
Having admitted their failure

00:01:23.059 --> 00:01:26.449
and abdicated, practices of
the unscrupulous money changers

00:01:26.449 --> 00:01:28.608
stand indicted in the
court of public opinion,

00:01:28.608 --> 00:01:31.975
rejected by the hearts and minds of man.

00:01:31.975 --> 00:01:33.554
Restoration calls however,

00:01:33.554 --> 00:01:35.156
not for changes in ethics alone.

00:01:35.156 --> 00:01:38.036
This nation asks for
action and action now.

00:01:38.036 --> 00:01:40.729
What's interesting about this paragraph

00:01:40.729 --> 00:01:43.516
is that there's a lot of Bible stuff going

00:01:43.516 --> 00:01:44.909
on in here.

00:01:44.909 --> 00:01:47.393
There's a lot of biblical references

00:01:47.393 --> 00:01:49.831
that serve to do I think a lot of work

00:01:49.831 --> 00:01:53.245
for Roosevelt in this inaugural address.

00:01:53.245 --> 00:01:55.218
- [Voiceover] As you talked,
I just underlined the things

00:01:55.218 --> 00:01:57.564
that really stood out
to me as maybe kind of

00:01:57.564 --> 00:01:59.166
the heart of what he was saying,

00:01:59.166 --> 00:02:01.697
and you're saying these are
like Biblical references.

00:02:01.697 --> 00:02:02.765
What do you mean by that?

00:02:02.765 --> 00:02:03.717
- [Voiceover] Some of them are.

00:02:03.717 --> 00:02:05.621
When we're talking about plague of locusts

00:02:05.621 --> 00:02:07.432
and money changers specifically,

00:02:07.432 --> 00:02:10.753
we're looking at old and
new testament references

00:02:10.753 --> 00:02:12.750
respectively, in fact,
later in this speech,

00:02:12.750 --> 00:02:16.441
he refers to money changers
being chased out of our nation's

00:02:16.441 --> 00:02:20.110
temple which is a deliberate
reference to the New Testament.

00:02:20.110 --> 00:02:23.593
- [Voiceover] This is very grand.

00:02:23.593 --> 00:02:26.147
We love to hear this speech so much,

00:02:26.147 --> 00:02:28.168
because it has that kind of ringing

00:02:28.168 --> 00:02:30.164
of authenticity in a way that maybe

00:02:30.164 --> 00:02:32.324
a modern speech does not.

00:02:32.324 --> 00:02:34.019
- [Voiceover] Some of
that authenticity comes

00:02:34.019 --> 00:02:37.804
through association with ethic literature

00:02:37.804 --> 00:02:39.197
and the Bible.

00:02:39.197 --> 00:02:41.844
He's making these illusions
to great Biblical events.

00:02:41.844 --> 00:02:44.793
Like the plague of locusts
being visited upon Egypt

00:02:44.793 --> 00:02:47.208
which was like a great
and terrible plague,

00:02:47.208 --> 00:02:49.460
and he's using that as a counter point

00:02:49.460 --> 00:02:53.384
to the misery of the present moment.

00:02:53.384 --> 00:02:54.522
He's saying, look,

00:02:54.522 --> 00:02:55.823
things could be worse.

00:02:55.823 --> 00:02:57.866
We could be ancient Egypt in the Bible,

00:02:57.866 --> 00:03:00.699
and locusts could be
eating all of our crops.

00:03:00.699 --> 00:03:02.324
Things are bad, but it's not like

00:03:02.324 --> 00:03:05.714
God himself is willing
destruction upon us.

00:03:05.714 --> 00:03:07.502
- [Voiceover] Yeah, I think this is also

00:03:07.502 --> 00:03:09.360
another one of the
really interesting things

00:03:09.360 --> 00:03:10.799
about the great depression.

00:03:10.799 --> 00:03:13.586
It's true that there were farm failures

00:03:13.586 --> 00:03:17.464
during the dust bowl,
but on the whole it's

00:03:17.464 --> 00:03:19.739
not like people stopped producing food.

00:03:19.739 --> 00:03:21.039
This wasn't a famine.

00:03:21.039 --> 00:03:23.408
What it was was a crisis
of confidence where

00:03:23.408 --> 00:03:26.589
prices went down significantly,

00:03:26.589 --> 00:03:30.026
and so farmers could not
make a living on their crops.

00:03:30.026 --> 00:03:31.721
It's not that they didn't have food.

00:03:31.721 --> 00:03:33.067
It's that they didn't have money,

00:03:33.067 --> 00:03:35.552
and I also feel like there's a different

00:03:35.552 --> 00:03:39.197
aspect to the reason that
he uses this biblical

00:03:39.197 --> 00:03:40.660
language here, and I think that's because

00:03:40.660 --> 00:03:42.518
it's very authoritative.

00:03:42.518 --> 00:03:45.606
When you stand up in
front of a group of people

00:03:45.606 --> 00:03:48.903
and Roosevelt has this powerful voice

00:03:48.903 --> 00:03:51.202
which really resonates with people,

00:03:51.202 --> 00:03:53.849
and you speak like a preacher would speak.

00:03:53.849 --> 00:03:57.007
It says, this is a man of authority.

00:03:57.007 --> 00:03:59.956
This is a man who perhaps
is in touch with the moral

00:03:59.956 --> 00:04:02.928
authority associated
with the Christian Bible.

00:04:02.928 --> 00:04:05.273
- [Voiceover] Sure, for a very long time,

00:04:05.273 --> 00:04:08.222
authority was kind of
correlated with your ability

00:04:08.222 --> 00:04:09.592
to quote chapter and verse.

00:04:09.592 --> 00:04:11.032
I mean we're talking
about a man who is just

00:04:11.032 --> 00:04:12.959
put his hand on a Bible in order to

00:04:12.959 --> 00:04:15.537
swear himself in.

00:04:15.537 --> 00:04:17.464
- [Voiceover] It really makes him seem

00:04:17.464 --> 00:04:19.670
not only like he knows
what he's talking about,

00:04:19.670 --> 00:04:22.549
but also that he's got a
handle on the situation.

00:04:22.549 --> 00:04:25.196
- [Voiceover] What we're
saying that by harnessing

00:04:25.196 --> 00:04:27.402
the language, he's trying
to harness the authority

00:04:27.402 --> 00:04:29.167
that people have invested

00:04:29.167 --> 00:04:31.837
in the church by using the
language of the church.

00:04:31.837 --> 00:04:32.905
- [Voiceover] What we're doing here,

00:04:32.905 --> 00:04:37.224
I might call step three
which is to identify

00:04:37.224 --> 00:04:40.800
how an argument is made.

00:04:40.800 --> 00:04:45.800
We're looking at his rhetorical strategies

00:04:48.602 --> 00:04:52.410
and seeing how they're
effective or in perhaps

00:04:52.410 --> 00:04:56.450
another case, not effective
in conveying his opinion,

00:04:56.450 --> 00:04:57.402
and I say opinion.

00:04:57.402 --> 00:05:00.816
At this point, what would
we say that his opinion of

00:05:00.816 --> 00:05:02.812
the Great Depression is?

00:05:02.812 --> 00:05:05.297
- [Voiceover] That it's
specific people's fault,

00:05:05.297 --> 00:05:07.178
that it is at the fault of not just this

00:05:07.178 --> 00:05:11.566
wave of panic, but on a
count of some greedy people,

00:05:11.566 --> 00:05:12.960
the unscrupulous money changers

00:05:12.960 --> 00:05:16.303
and the rulers of the exchanges.

00:05:16.303 --> 00:05:18.579
He's blaming bankers for
the great depression,

00:05:18.579 --> 00:05:20.715
which I think is fair.

00:05:20.715 --> 00:05:23.130
There's very little
regulation in the 1920s

00:05:23.130 --> 00:05:25.731
that would prevent the kind of fraud

00:05:25.731 --> 00:05:28.166
that could lead to a collapse of banking.

00:05:28.166 --> 00:05:31.370
For example, insider
trading is not illegal,

00:05:31.370 --> 00:05:34.412
and most people bought stocks on margin

00:05:34.412 --> 00:05:35.735
which is a terrible idea

00:05:35.735 --> 00:05:38.336
which means you only have
to put 10% of the value

00:05:38.336 --> 00:05:41.146
of a bond down before you buy it,

00:05:41.146 --> 00:05:42.910
which means that there's
a lot of theoretical

00:05:42.910 --> 00:05:45.465
money floating around out
there that's not backed by

00:05:45.465 --> 00:05:46.695
much real money.

00:05:46.695 --> 00:05:48.414
- [Voiceover] That sounds
like a terrible idea.

00:05:48.414 --> 00:05:49.830
- [Voiceover] It was a terrible idea.

00:05:49.830 --> 00:05:52.872
- [Voiceover] It's like
buying stocks on credit.

00:05:52.872 --> 00:05:53.708
- [Voiceover] Exactly.

00:05:53.708 --> 00:05:55.054
- [Voiceover] Oh, man.

00:06:00.790 --> 00:06:02.717
- [Voiceover] His argument
is that first, things could

00:06:02.717 --> 00:06:03.297
be worse.

00:06:03.297 --> 00:06:04.575
Second of all, the reason things are bad

00:06:04.575 --> 00:06:05.968
is because of these people.

00:06:05.968 --> 00:06:07.918
Thing number three,
here's how we're going to

00:06:07.918 --> 00:06:09.544
get back on track.

00:06:09.544 --> 00:06:12.980
- [Voiceover] This is where
we get here at the end.

00:06:12.980 --> 00:06:15.720
The nation asks for action,

00:06:15.720 --> 00:06:17.601
and action now, which it says not only

00:06:17.601 --> 00:06:22.431
a mention of how he's
going to get things done

00:06:22.431 --> 00:06:26.378
but a covert poke at Herbert Hoover for

00:06:26.378 --> 00:06:28.816
not doing much, and then he says,

00:06:28.816 --> 00:06:32.624
our greatest primary task
is to put people to work.

00:06:32.624 --> 00:06:35.504
Remember there's an
unemployment rate of 25%.

00:06:35.504 --> 00:06:36.479
- [Voiceover] That is so many people.

00:06:36.479 --> 00:06:38.127
- [Voiceover] Our current
unemployment rate is less

00:06:38.127 --> 00:06:40.751
than 5% to give you an idea.

00:06:40.751 --> 00:06:45.024
This is no unsolvable
problem if we face it wisely

00:06:45.024 --> 00:06:46.394
and courageously.

00:06:46.394 --> 00:06:48.344
it can be accomplished in part by direct

00:06:48.344 --> 00:06:50.898
recruiting by the government itself,

00:06:50.898 --> 00:06:53.522
treating the task as we
would treat the emergency

00:06:53.522 --> 00:06:56.634
of a war, but at the same time,

00:06:56.634 --> 00:06:58.979
through this employment,
accomplishing greatly

00:06:58.979 --> 00:07:02.346
needed projects to stimulate
and reorganize the use

00:07:02.346 --> 00:07:04.134
of our natural resources.

00:07:04.134 --> 00:07:05.736
- [Voiceover] This is a radical idea.

00:07:05.736 --> 00:07:07.431
- [Voiceover] It is a really radical idea,

00:07:07.431 --> 00:07:10.403
and this is one reason why
historians love to study

00:07:10.403 --> 00:07:11.541
the great depression

00:07:11.541 --> 00:07:15.372
and the administration of
Franklin Delano Roosevelt,

00:07:15.372 --> 00:07:19.157
because this is kind of
the decade where we threw

00:07:19.157 --> 00:07:21.433
out the rulebook, and
I think what Roosevelt

00:07:21.433 --> 00:07:24.637
is saying here is he was willing to try

00:07:24.637 --> 00:07:28.259
anything to conquer the great depression,

00:07:28.259 --> 00:07:31.185
and one of the things he tries is

00:07:31.185 --> 00:07:33.252
bringing the government into the process

00:07:33.252 --> 00:07:35.156
of giving people work.

00:07:35.156 --> 00:07:38.337
We've got a sense of what he's arguing

00:07:38.337 --> 00:07:41.287
and how he's arguing it.

00:07:41.287 --> 00:07:44.629
Let's take a higher level look now.

00:07:44.629 --> 00:07:47.741
Let's say step four is seeing

00:07:47.741 --> 00:07:50.063
if you can analyze

00:07:50.063 --> 00:07:53.917
the potential bias of a source,

00:07:53.917 --> 00:07:57.617
and I wanna be clear that

00:08:00.599 --> 00:08:02.633
all sources are biased.

00:08:02.633 --> 00:08:05.837
I think a common misconception is that

00:08:05.837 --> 00:08:08.182
if you're looking at a source,

00:08:08.182 --> 00:08:09.900
it's either biased or it's not.

00:08:09.900 --> 00:08:12.849
It's written by someone who has an agenda

00:08:12.849 --> 00:08:16.031
or someone whose completely impartial,

00:08:16.031 --> 00:08:18.654
and that is never the case.

00:08:18.654 --> 00:08:19.606
- [Voiceover] What about a photograph?

00:08:19.606 --> 00:08:21.371
If I take a photograph
of something or someone,

00:08:21.371 --> 00:08:23.879
isn't that then objective rendering

00:08:23.879 --> 00:08:25.899
of that person or object?

00:08:25.899 --> 00:08:28.291
- [Voiceover] It certainly
shows what was there

00:08:28.291 --> 00:08:29.986
at that moment in time,

00:08:29.986 --> 00:08:32.447
but even photographers are making choices.

00:08:32.447 --> 00:08:34.839
When you pick up a camera
and you take a picture

00:08:34.839 --> 00:08:36.952
of a thing, you are taking a picture

00:08:36.952 --> 00:08:39.692
of that thing and not something else,

00:08:39.692 --> 00:08:42.037
which in itself a form of bias

00:08:42.037 --> 00:08:45.009
to say I think this is
important or this is what I want

00:08:45.009 --> 00:08:46.147
you to see.

00:08:46.147 --> 00:08:49.630
- [Voiceover] Where we
put the frame is a choice.

00:08:49.630 --> 00:08:54.483
The question is what is Roosevelt
not saying in this speech?

00:08:54.483 --> 00:08:56.433
What is he not taking a photograph of?

00:08:56.433 --> 00:08:59.220
What's just outside
the view of his camera?

00:08:59.220 --> 00:09:02.238
- [Voiceover] And why is
he taking this photograph

00:09:02.238 --> 00:09:03.051
of a speech?

00:09:03.051 --> 00:09:05.164
When he sat down to write this, what was

00:09:05.164 --> 00:09:07.602
motivating him?

00:09:07.602 --> 00:09:09.460
And what are some of the perhaps even

00:09:09.460 --> 00:09:13.523
less obvious factors
about why he makes the

00:09:13.523 --> 00:09:15.497
argument that he does.

00:09:15.497 --> 00:09:17.194
- [Voiceover] Obviously,
the man has a bias

00:09:17.194 --> 00:09:19.781
in favor of his own politics.

00:09:19.781 --> 00:09:22.289
These are his administrations, ideas.

00:09:22.289 --> 00:09:27.289
He's going to be coming out in
favor of those very strongly.

00:09:27.620 --> 00:09:30.259
- [Voiceover] FDR is a democrat.

00:09:33.237 --> 00:09:35.680
There really haven't been many democrats

00:09:35.680 --> 00:09:39.181
in office since before
the Lincoln administration

00:09:39.181 --> 00:09:41.155
since the 1860s.

00:09:41.155 --> 00:09:42.943
That's a new thing.

00:09:42.943 --> 00:09:46.913
This is the popular base rejecting
Hoover and the Republican

00:09:46.913 --> 00:09:48.794
party because of the Great Depression.

00:09:48.794 --> 00:09:50.280
- [Voiceover] Right.

00:09:50.280 --> 00:09:51.929
- [Voiceover] He's bringing democratic

00:09:51.929 --> 00:09:54.460
political ideas to the table here.

00:09:54.460 --> 00:09:56.016
- [Voiceover] He's trying to make a case

00:09:56.016 --> 00:09:58.593
for those political ideas in this speech.

00:09:58.593 --> 00:10:00.822
He was elected by the majority
of American voters, but now

00:10:00.822 --> 00:10:03.446
he has to make the case to
the rest of the United States.

00:10:03.446 --> 00:10:04.489
He has to make a case to the people

00:10:04.489 --> 00:10:06.439
that didn't elect him.

00:10:06.439 --> 00:10:09.806
- [Voiceover] He's saying
that direct recruiting by

00:10:09.806 --> 00:10:12.616
the government itself, government jobs,

00:10:12.616 --> 00:10:16.563
having the powers as if
the depression were war,

00:10:16.563 --> 00:10:20.278
that is a case for really
strong government intervention

00:10:20.278 --> 00:10:22.949
which is a key stone
of the democratic party

00:10:22.949 --> 00:10:24.853
compared to Republicans who generally

00:10:24.853 --> 00:10:27.175
advocate for a smaller government.

00:10:27.175 --> 00:10:29.334
He's saying this is what's gonna work.

00:10:29.334 --> 00:10:31.888
The democratic platform
of using the government

00:10:31.888 --> 00:10:34.512
in the economy and in social programs

00:10:34.512 --> 00:10:36.254
is what's going to work to get us out

00:10:36.254 --> 00:10:37.090
of this depression.

00:10:37.090 --> 00:10:39.110
- [Voiceover] He's making
a big strong case for

00:10:39.110 --> 00:10:40.248
federalism.

00:10:40.248 --> 00:10:42.477
- [Voiceover] Exactly, what
I think is interesting though

00:10:42.477 --> 00:10:45.333
here is that there's a lot he doesn't say,

00:10:45.333 --> 00:10:46.912
and I think that's also important

00:10:46.912 --> 00:10:49.692
to look at when you're
analyzing a primary source.

00:10:49.692 --> 00:10:52.014
There's a lot that you could talk about,

00:10:52.014 --> 00:10:54.058
but you make choices
about what to talk about

00:10:54.058 --> 00:10:55.613
and what not to mention.

00:10:55.613 --> 00:10:57.680
What could you say he
doesn't mention here?

00:10:57.680 --> 00:10:59.909
- [Voiceover] He doesn't mention how

00:10:59.909 --> 00:11:01.743
any of this is going to work.

00:11:01.743 --> 00:11:04.182
- [Voiceover] Yeah, I think
that's maybe the biggest

00:11:04.182 --> 00:11:06.109
missing piece here.

00:11:06.109 --> 00:11:08.593
This is broad strokes.

00:11:08.593 --> 00:11:10.265
This is getting people on board,

00:11:10.265 --> 00:11:12.239
but no where does he say, okay

00:11:12.239 --> 00:11:13.911
here's exactly what I'm going to do.

00:11:13.911 --> 00:11:15.931
Let me tell you how many dollars

00:11:15.931 --> 00:11:16.697
I'm going to spend, how many people

00:11:16.697 --> 00:11:18.996
I'm going to hire, what sort of cabinets

00:11:18.996 --> 00:11:20.389
I'm going to create.

00:11:20.389 --> 00:11:23.129
This is not a time for specifics he says.

00:11:23.129 --> 00:11:26.032
This is almost more of an
inspirational speech to say

00:11:26.032 --> 00:11:27.796
okay, I gotcha.

00:11:27.796 --> 00:11:31.511
We've looked at the source.

00:11:31.511 --> 00:11:34.227
We've analyzed it's rhetorical strategies,

00:11:34.227 --> 00:11:35.970
and it's potential bias.

00:11:35.970 --> 00:11:37.572
The last thing we might wanna do with this

00:11:37.572 --> 00:11:41.008
is now think about how we
could use it as a source.

00:11:41.008 --> 00:11:44.166
- [Voiceover] We're taking
this primary source,

00:11:44.166 --> 00:11:46.117
and we're turning it
into a secondary source.

00:11:46.117 --> 00:11:47.580
- [Voiceover] Right, so

00:11:47.580 --> 00:11:50.598
say that you are sitting down to

00:11:50.598 --> 00:11:53.478
write an essay about the Great Depression,

00:11:53.478 --> 00:11:56.798
and you've gotta say, now can I use

00:11:56.798 --> 00:11:58.772
Franklin Delano Roosevelt's inaugural

00:11:58.772 --> 00:12:01.837
address to make my point in my essay?

00:12:01.837 --> 00:12:04.571
Step five

00:12:07.247 --> 00:12:10.005
let's say synthesize perhaps.

00:12:10.962 --> 00:12:12.071
Using my big words,

00:12:13.147 --> 00:12:17.162
as a tool for your own argument.

00:12:17.162 --> 00:12:21.852
- [Voiceover] I would say
that this speech is the frame

00:12:21.852 --> 00:12:25.219
that Roosevelt is putting
on the depression.

00:12:25.219 --> 00:12:27.634
This is how he is creating the narrative

00:12:27.634 --> 00:12:29.886
that he wants Americans to adopt

00:12:29.886 --> 00:12:32.371
or he is identifying the
crisis and this is how

00:12:32.371 --> 00:12:34.182
he wants people to see it.

00:12:34.182 --> 00:12:38.013
- [Voiceover] Yeah, so this
might be a great primary source

00:12:38.013 --> 00:12:42.634
to tell you about
Roosevelt's strategy or his

00:12:42.634 --> 00:12:44.887
communication strategy.

00:12:44.887 --> 00:12:47.394
What might it not be a
very good primary source

00:12:47.394 --> 00:12:49.531
to help you make an agrument for?

00:12:49.531 --> 00:12:52.712
- [Voiceover] It probably
wouldn't be a very good primary

00:12:52.712 --> 00:12:55.846
source for the Republican legislative

00:12:55.846 --> 00:12:57.286
response.

00:12:57.286 --> 00:13:01.048
You might wanna go with
Senator Reid Smoot of Utah

00:13:01.048 --> 00:13:02.510
for something like that.

00:13:02.510 --> 00:13:06.551
- [Voiceover] Right, and it's
probably not a great source

00:13:06.551 --> 00:13:10.614
for really diving into the
specifics of the new deal.

00:13:10.614 --> 00:13:13.099
He doesn't say anything about the civilian

00:13:13.099 --> 00:13:14.446
conservation corp.

00:13:14.446 --> 00:13:17.255
He doesn't say anything
about the national recovery

00:13:17.255 --> 00:13:18.695
administration.

00:13:18.695 --> 00:13:21.388
This is not the nuts and
bolts of the new deal.

00:13:21.388 --> 00:13:23.282
It's the grand idea behind it.

00:13:23.282 --> 00:13:25.975
- [Voiceover] Right, he's
trying to sell the new deal.

00:13:25.975 --> 00:13:28.622
- [Voiceover] It's I think,
a really powerful primary

00:13:28.622 --> 00:13:32.175
source for understanding
the impetus behind

00:13:32.175 --> 00:13:35.008
the new deal, but not the programs.

00:13:35.008 --> 00:13:37.051
- [Voiceover] Sweet.

00:13:37.051 --> 00:13:38.096
- [Voiceover] Alright, well
thank you for bringing your

00:13:38.096 --> 00:13:40.488
sweet grammarian skills to the table

00:13:40.488 --> 00:13:42.949
as we look at Roosevelt's speech.

00:13:42.949 --> 00:13:44.064
- [Voiceover] My pleasure,
thank you for bringing

00:13:44.064 --> 00:13:46.246
your sweet historian skills to the table.

00:13:46.246 --> 00:13:47.616
- [Voiceover] Kim and David out.

00:13:47.616 --> 00:13:48.697
- [Voiceover] Scholarly high five!


Introduction to verb tense

WEBVTT
Kind: captions
Language: en

00:00:00.000 --> 00:00:01.315
- [Voiceover] Hello grammarians.

00:00:01.315 --> 00:00:04.879
Today I wanna introduce
the idea of the verb tense,

00:00:04.879 --> 00:00:07.700
and the way I wanna do that
is to express the following,

00:00:07.700 --> 00:00:10.696
if you can master grammatical tenses,

00:00:10.696 --> 00:00:15.595
you will become a time wizard,
a literal, actual time wizard

00:00:15.595 --> 00:00:17.697
because tense is nothing
more than the ability

00:00:17.697 --> 00:00:21.481
of verbs to situate themselves in time,

00:00:21.481 --> 00:00:23.792
specifically in three different times

00:00:23.792 --> 00:00:28.075
so in the past, the present,
or the future it can happen.

00:00:28.075 --> 00:00:29.011
When we're talking about a verb,

00:00:29.011 --> 00:00:32.749
a verb can happen now,
a verb can happen later,

00:00:32.749 --> 00:00:35.092
and a verb can have
happened in the past, then.

00:00:36.571 --> 00:00:40.177
That's basically it, and
if you master tenses,

00:00:40.177 --> 00:00:44.821
you will be able to tell
stories that span all of time,

00:00:44.821 --> 00:00:49.337
and I think that ability
is kind of astonishing

00:00:49.337 --> 00:00:52.635
that language can express
that sort of idea.

00:00:52.635 --> 00:00:55.223
To just give a very simple example,

00:00:55.223 --> 00:00:58.625
I'll just take the word talk and

00:00:58.625 --> 00:01:02.178
put it in these three basic tenses.

00:01:02.178 --> 00:01:03.941
Now, it does get more
complicated than this,

00:01:03.941 --> 00:01:05.614
sure, but we'll cover that later,

00:01:05.614 --> 00:01:09.685
so if i take the verb to talk

00:01:11.118 --> 00:01:14.531
and I put it in the
present, I would just say,

00:01:14.531 --> 00:01:16.952
"I talk,"

00:01:18.007 --> 00:01:20.514
the most basic iteration, "I talk."

00:01:20.514 --> 00:01:24.228
In the future, "I will talk,"

00:01:25.639 --> 00:01:29.764
and in the past, "I talked."

00:01:29.764 --> 00:01:32.772
This is the simple form of every

00:01:32.772 --> 00:01:37.278
English tense, past, present, future.

00:01:37.278 --> 00:01:41.759
If you can command all of these,
you will be a time wizard.

00:01:41.759 --> 00:01:44.506
That's you, you can learn anything.

00:01:44.506 --> 00:01:45.720
David out.


Introduction to verbs

WEBVTT
Kind: captions
Language: en

00:00:00.000 --> 00:00:01.351
- [Voiceover] Hello, grammarians.

00:00:01.351 --> 00:00:03.626
Today I'd like to
introduce you to the verb,

00:00:03.626 --> 00:00:05.786
which is another part of speech.

00:00:05.786 --> 00:00:08.154
But I suppose the most
fruitful place for us to begin

00:00:08.154 --> 00:00:12.984
is by asking, "What is a verb?"

00:00:14.184 --> 00:00:16.142
A verb is a part of
speech that has a bunch of

00:00:16.142 --> 00:00:19.196
different functions, but one
of its most important functions

00:00:19.196 --> 00:00:23.363
is that it can express or show action.

00:00:23.363 --> 00:00:28.363
Verbs can show action.

00:00:29.052 --> 00:00:30.933
In order to demonstrate
this, I have brought along

00:00:30.933 --> 00:00:32.767
a little cartoon bear,

00:00:32.767 --> 00:00:35.438
and I'm going to use this
bear in several sentences,

00:00:35.438 --> 00:00:37.806
each of which will contain a verb.

00:00:37.806 --> 00:00:41.846
Because all sentences contain verbs.

00:00:41.846 --> 00:00:44.075
So I'm gonna write a couple
of sentences about the bear,

00:00:44.075 --> 00:00:45.910
and every time I use a
verb, I'm gonna write it

00:00:45.910 --> 00:00:48.000
in yellow like that.

00:00:48.000 --> 00:00:49.184
Here we go.

00:00:49.184 --> 00:00:51.061
The bear roars.

00:00:55.151 --> 00:00:57.650
The bear runs.

00:01:01.490 --> 00:01:03.741
The bear sleeps.

00:01:04.811 --> 00:01:08.768
Now, each one of these
words in yellow is a verb.

00:01:10.848 --> 00:01:13.356
Each one of them is an action,

00:01:13.356 --> 00:01:15.747
and this is the first
thing that verbs can do.

00:01:15.747 --> 00:01:18.952
Verbs can show action in sentences.

00:01:18.952 --> 00:01:22.876
And, in fact, all sentences
must contain verbs.

00:01:22.876 --> 00:01:24.408
You can learn anything.

00:01:24.408 --> 00:01:25.868
David out.