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00:00:10,440 --> 00:00:23,590
Monomer of nucleic acids is
called a nucleotide, which I

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00:00:23,590 --> 00:00:24,860
will abbreviate NTIDE.

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00:00:27,380 --> 00:00:30,500
And a nucleotide comprises
three parts--

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00:00:30,500 --> 00:00:33,505
a phosphate, a sugar,
and a base.

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00:00:46,650 --> 00:00:54,650
Phosphate, sugar, base --that we
will abbreviate P-S-B. The

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00:00:54,650 --> 00:01:12,590
polymer of nucleotides makes up
ribonucleic acid, RNA; or

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00:01:12,590 --> 00:01:15,360
deoxyribonucleic acid, DNA.

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00:01:15,360 --> 00:01:17,170
You need to know the full
names of those.

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00:01:17,170 --> 00:01:19,040
I'm not going to
write them out.

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00:01:19,040 --> 00:01:23,430
And those are all
polynucleotides.

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00:01:29,950 --> 00:01:32,420
And the way that polynucleotides
are put

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together is through the joining
of the phosphate and

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sugar into a sugar phosphate
backbone, from

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which the bases hang.

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And so they look kind
of like this.

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There's phosphate,
sugar, phosphate,

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00:01:50,840 --> 00:01:53,860
sugar, phosphate, sugar.

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And from the sugar
hangs the base.

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The phosphate and the sugar, as
I've just said, forms the

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sugar phosphate backbone.

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00:02:09,680 --> 00:02:15,005
And the bases, as we'll discuss
in a moment, comprise

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the information that is encoded
in nucleic acids.

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00:02:28,110 --> 00:02:31,230
Let's talk more about this
nucleotide and the structure

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00:02:31,230 --> 00:02:34,810
of the nucleotide and the kinds
of components there are

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00:02:34,810 --> 00:02:37,050
in the nucleotide.

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The sugar of the nucleotide
is a pentose.

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00:02:41,940 --> 00:02:44,920
It's a five carbon sugar.

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It is called ribose,
and it's cyclic.

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And it's called ribose in RNA,
and as you will see,

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deoxyribose in DNA.

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There are four bases in DNA.

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They are called adenine,
guanine,

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cytosine, and thymine.

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And they are abbreviated
A, G, C, and T--

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00:03:39,490 --> 00:03:40,620
by their first initial.

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00:03:40,620 --> 00:03:43,260
But you need to know
the whole name.

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In RNA, the bases are the same,

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except instead of thymine--

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there is no thymine.

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00:03:55,200 --> 00:03:58,660
Instead, there is something
called uracil, which is

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00:03:58,660 --> 00:04:04,180
closely related, and
abbreviated U.

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00:04:04,180 --> 00:04:07,250
The bases have a particular
structure.

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00:04:07,250 --> 00:04:10,760
You do not need to be able to
draw them, but you should be

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00:04:10,760 --> 00:04:13,480
able to recognize the
class of base.

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00:04:16,010 --> 00:04:20,640
There is a class called
purines, which

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00:04:20,640 --> 00:04:21,950
comprise two rings.

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00:04:21,950 --> 00:04:23,680
I'll show you some slides
in a moment.

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00:04:27,200 --> 00:04:31,430
And adenine and guanine fall
into that category.

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00:04:31,430 --> 00:04:39,230
And then, there's another class
called pyrimidines,

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00:04:39,230 --> 00:04:42,880
which are made of one ring.

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00:04:42,880 --> 00:04:48,205
And cytosine, thymine, and
uracil fall into that class.

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00:04:56,510 --> 00:04:58,860
Let's draw the structure
of a nucleotide

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00:04:58,860 --> 00:05:00,500
out in chemical formula.

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00:05:00,500 --> 00:05:01,930
We're not going to
draw the bases.

55
00:05:01,930 --> 00:05:05,270
We're going to draw mostly the
sugar and the phosphate,

56
00:05:05,270 --> 00:05:07,570
because it will be important
when we think about

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00:05:07,570 --> 00:05:09,400
polymerizing nucleotides.

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00:05:09,400 --> 00:05:11,500
And then I'll show
you some slides.

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00:05:11,500 --> 00:05:12,970
So nucleotide structure--

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the best way to draw a
nucleotide structure is to

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start with the sugar.

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So start with an oxygen.

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And then you can put
in the carbons.

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00:05:35,450 --> 00:05:39,990
And the carbons are numbered,
because, in many

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00:05:39,990 --> 00:05:43,440
macromolecules, there are so
many carbons, it can be very

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00:05:43,440 --> 00:05:45,720
useful to give them
specific numbers.

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00:05:45,720 --> 00:05:47,950
And that's true in the sugar.

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00:05:47,950 --> 00:05:49,770
It's also true in the bases.

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00:05:49,770 --> 00:05:52,590
But the sugar numberings
of the carbons are very

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00:05:52,590 --> 00:05:53,890
important for you.

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00:05:53,890 --> 00:05:59,510
There's a one prime carbon, two
prime, three prime, four

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00:05:59,510 --> 00:06:02,730
prime, and five prime.

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00:06:02,730 --> 00:06:06,045
The base is attached to
the one prime carbon.

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00:06:09,450 --> 00:06:12,595
And the phosphate is attached
to the five prime carbon.

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00:06:26,390 --> 00:06:30,700
The two prime and the three
prime carbon are also notable.

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00:06:30,700 --> 00:06:34,680
The three prime carbon always
has a hydroxyl group.

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00:06:34,680 --> 00:06:41,060
And it's this hydroxyl group and
this hydroxyl group of the

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phosphate that react together
when the sugar phosphate

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00:06:45,180 --> 00:06:48,370
backbone forms covalent bonds.

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00:06:48,370 --> 00:06:54,110
The two prime carbon can either
have a hydrogen, as in

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00:06:54,110 --> 00:07:06,630
DNA, or a hydroxyl as RNA.

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00:07:06,630 --> 00:07:10,065
Hydroxyl groups are reactive,
and having this extra hydroxyl

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00:07:10,065 --> 00:07:14,720
group on RNA makes this
sugar more reactive

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00:07:14,720 --> 00:07:16,001
than the one in DNA.

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00:07:19,440 --> 00:07:20,240
OK.

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00:07:20,240 --> 00:07:23,450
That is your nucleotide
structure.

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00:07:23,450 --> 00:07:25,996
And you should know it.

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Let's see what we have
for slides here.

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Nucleic acid monomer
and polymer.

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00:07:34,190 --> 00:07:37,420
We're going to draw in one
moment the nucleic acid

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00:07:37,420 --> 00:07:40,210
polymer on the board,
but here it is.

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00:07:40,210 --> 00:07:47,080
Here is the sugar, the base,
and the phosphate group.

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00:07:47,080 --> 00:07:47,500
All right.

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00:07:47,500 --> 00:07:50,190
Let's think about how you
actually get this sugar

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00:07:50,190 --> 00:07:52,610
phosphate backbone formed.

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00:07:52,610 --> 00:07:57,490
And let us draw formation
of a dinucleotide.

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00:08:00,080 --> 00:08:03,490
And I'm going to abbreviate on
one of the nucleotides the

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00:08:03,490 --> 00:08:07,840
phosphate as PO4, otherwise we
won't fit this on the board.

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00:08:07,840 --> 00:08:12,160
So let's put the sugars first.

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00:08:12,160 --> 00:08:17,030
And let me actually just make
sure that you guys understand

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00:08:17,030 --> 00:08:20,040
that the sugar can be drawn as
I've drawn it, with all the

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00:08:20,040 --> 00:08:25,360
carbons there, or it can be
drawn in this way, where the

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00:08:25,360 --> 00:08:30,810
carbons are the apices, or
at the ends of a line.

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00:08:30,810 --> 00:08:34,350
If this is a new you-- if this
is new organic chemistry

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00:08:34,350 --> 00:08:37,640
formula to you or chemical
formula to you, then please

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00:08:37,640 --> 00:08:40,490
come and see one of us, and
we'll make sure that you get

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00:08:40,490 --> 00:08:42,770
up to speed, because you really
do need to know that

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00:08:42,770 --> 00:08:44,400
for this course.

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Okay so let us draw
some sugars.

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Actually, I'm going to erase
this one and put it even

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closer to the top of the board,
because these are small

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boards no--

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new boards, nice but small.

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Okay.

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00:09:03,680 --> 00:09:09,125
And we're going to put here
a phosphate group.

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I'm going to extend this.

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00:09:10,925 --> 00:09:14,560
And we'll put a phosphate
group here.

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And we're going to put a base.

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And we're going to put a
three prime hydroxyl.

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00:09:23,130 --> 00:09:25,730
So here is the five
prime carbon and

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the three prime hydroxyl.

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And this is going to
be nucleotide one.

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And then we'll draw an identical
one below it, which

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will be nucleotide two,
where now I'll

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draw out the phosphate.

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Let's again start with the
sugar and a hydroxyl.

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And then let's put
in the phosphate.

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Okay.

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And this is going to
be nucleotide two--

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so nucleotide one and
nucleotide two.

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The phosphate, hydroxyl,
and the sugar--

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and we can put in some
negatives here.

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On the phosphate, that's fine.

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Depends on the pH as to what
the ionization of the

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phosphate group is.

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This hydroxyl group and
this phosphate group,

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are going to interact.

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And the outcome is going to be
a dinucleotide, where the two

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nucleotides, as you will see,
are joined by a particular

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linkage called a phosphodiester
linkage or a

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phosphodiester bond.

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We'll leave a phosphate
there attached to

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the five prime carbon.

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Here's the first base.

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And now, we've got--

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and I've got to fit it in.

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Okay.

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00:11:26,820 --> 00:11:28,810
So here is our dinucleotide--

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slightly skewed, but OK.

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00:11:31,050 --> 00:11:33,850
And there are three features
that I want to point out to

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00:11:33,850 --> 00:11:35,980
you on this dinucleotide.

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The first is the bond that
joins them together,

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which is this guy.

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00:11:42,470 --> 00:11:51,710
It is called a phosphodiester
bond or

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00:11:51,710 --> 00:11:55,830
phosphodiester linkage.

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00:11:55,830 --> 00:11:58,620
And the second is that
the two ends of this

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dinucleotide are different.

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On one end, there is a
free phosphate group.

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00:12:05,680 --> 00:12:08,930
And where there is a free
phosphate group, that is

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called the five prime
phosphate, or

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the five prime end.

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But the five prime end
has got a phosphate.

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That's part of its property.

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00:12:22,390 --> 00:12:25,040
On the other end, you'll
see, there is a

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free hydroxyl group.

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00:12:27,380 --> 00:12:31,540
And that is called the three
prime hydroxyl, or

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00:12:31,540 --> 00:12:34,610
the three prime end.

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00:12:34,610 --> 00:12:37,390
And they're equivalent,
pretty much.

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00:12:37,390 --> 00:12:40,210
But you should know that at
one side, there's a free

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hydroxyl group, the other side
a free phosphate group.

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00:12:42,990 --> 00:12:46,110
You will see later on that
this is pivotal in

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synthesizing DNA, as in DNA
replication and mitosis,

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meiosis, and so on.

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00:12:53,500 --> 00:12:54,730
All right.

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00:12:54,730 --> 00:12:55,900
Few more slides--

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00:12:55,900 --> 00:13:01,080
here are the sugars that are
found in nucleic acids.

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00:13:01,080 --> 00:13:04,030
There's the deoxyribose
and ribose.

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00:13:04,030 --> 00:13:06,370
I just put these up
for you for recap.

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Here are the bases.

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00:13:07,730 --> 00:13:10,010
Here are the pyrimidines--

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00:13:10,010 --> 00:13:11,920
cytosine, thymine,
and uracil--

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00:13:11,920 --> 00:13:14,250
and then the purines, with this

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00:13:14,250 --> 00:13:18,090
interesting di-ring structure.

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00:13:18,090 --> 00:13:20,200
This I drew for you, okay?

185
00:13:20,200 --> 00:13:21,800
And so it's on your
PowerPoint.

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If you're a bit shaky as to
what's on the board and how we

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00:13:24,760 --> 00:13:28,770
got there, you can go and get
this from the PowerPoints that

188
00:13:28,770 --> 00:13:30,020
I'll post after class.

189
00:13:35,920 --> 00:13:37,170
All right.

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00:13:40,150 --> 00:13:45,690
Now, in contrast to lipids and
carbohydrates, nucleic acids,

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00:13:45,690 --> 00:13:49,100
and as you will see, proteins,
have two extraordinary

192
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properties that allow them to
encode information in really a

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00:13:53,920 --> 00:13:56,920
way that is extremely rich.

194
00:13:56,920 --> 00:14:02,430
And those two properties I've
already touched on.

195
00:14:02,430 --> 00:14:06,180
One is that the ends
are different.

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00:14:06,180 --> 00:14:08,550
They're different in a
dinucleotide, and they're

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00:14:08,550 --> 00:14:11,730
different in a polynucleotide
that's a

198
00:14:11,730 --> 00:14:14,050
thousand nucleotides long.

199
00:14:14,050 --> 00:14:17,250
So they have different ends.

200
00:14:17,250 --> 00:14:22,020
And the bases have
a linear order.

201
00:14:25,020 --> 00:14:31,640
And this linear order is part
and parcel of the information

202
00:14:31,640 --> 00:14:34,570
that the nucleic acid encodes.

203
00:14:34,570 --> 00:14:37,380
So let's draw out,
for instance---

204
00:14:37,380 --> 00:14:43,220
and we're going to start
with five prime.

205
00:14:43,220 --> 00:14:53,830
Phosphate, sugar, phosphate,
sugar, phosphate, sugar

206
00:14:53,830 --> 00:14:54,300
phosphate--

207
00:14:54,300 --> 00:14:58,950
and we're going to end with the
sugar that has the three

208
00:14:58,950 --> 00:15:01,410
prime hydroxyl.

209
00:15:01,410 --> 00:15:04,960
Okay, so we've got a five prime
and a three prime end.

210
00:15:04,960 --> 00:15:09,585
And from this, the bases
are hanging.

211
00:15:13,480 --> 00:15:18,860
Now, when nucleotides are
incorporated into a nucleic

212
00:15:18,860 --> 00:15:22,580
acid polymer, there is an order
of synthesis, which is

213
00:15:22,580 --> 00:15:26,410
why the linear order of the
molecule eventually can be

214
00:15:26,410 --> 00:15:28,350
used for information.

215
00:15:28,350 --> 00:15:32,300
The base nearest the free
five prime phosphate

216
00:15:32,300 --> 00:15:33,550
is the first added.

217
00:15:37,320 --> 00:15:38,970
And the base--

218
00:15:38,970 --> 00:15:40,810
so it's part of the
nucleotide--

219
00:15:40,810 --> 00:15:45,740
nearest the three prime hydroxyl
is the last added.

220
00:15:45,740 --> 00:15:48,810
It's really important
that you know this.

221
00:15:48,810 --> 00:15:52,940
Furthermore, when we write out
nucleotides, nucleotide

222
00:15:52,940 --> 00:15:56,310
sequence, when we write out a
nucleic acid sequence, we

223
00:15:56,310 --> 00:15:59,360
don't generally write the sugar
phosphate backbone in.

224
00:15:59,360 --> 00:16:03,410
We just write the bases.

225
00:16:03,410 --> 00:16:08,678
So it's written five
prime, base, base,

226
00:16:08,678 --> 00:16:13,080
base, base, three prime.

227
00:16:13,080 --> 00:16:15,940
But of course, the bases
can be anything.

228
00:16:15,940 --> 00:16:24,320
So for example, we could have
five prime, adenine, guanine,

229
00:16:24,320 --> 00:16:27,430
guanine, cytosine,
three prime.

230
00:16:27,430 --> 00:16:29,780
And there's a convention that
you have to follow.

231
00:16:29,780 --> 00:16:32,120
And it doesn't matter how long
you're in this business.

232
00:16:32,120 --> 00:16:35,960
When you write out a nucleic
acid polymer, you always write

233
00:16:35,960 --> 00:16:38,770
the five prime and the
three prime end.

234
00:16:38,770 --> 00:16:42,860
I've been in this business for
30 years now, and I still have

235
00:16:42,860 --> 00:16:45,080
to write the five prime and
the three prime end.

236
00:16:45,080 --> 00:16:48,180
If you don't, you get lost, and
you will get mixed up in

237
00:16:48,180 --> 00:16:53,030
your calculations, both in this
course and in real life.

238
00:16:53,030 --> 00:16:56,670
Now, there are lots of
combinations of bases, even

239
00:16:56,670 --> 00:17:00,380
though there are only
four bases.

240
00:17:00,380 --> 00:17:06,040
For example, if there are four
bases and you have a three

241
00:17:06,040 --> 00:17:07,290
nucleotide polymer--

242
00:17:12,000 --> 00:17:16,579
four bases, three possibilities,
64

243
00:17:16,579 --> 00:17:17,829
possibilities.

244
00:17:23,930 --> 00:17:30,800
Genes can be thousands and
thousands of bases in length.

245
00:17:30,800 --> 00:17:35,550
And so the information, the
combinatorics involved in the

246
00:17:35,550 --> 00:17:38,700
nucleic acid polymer
is very large.

247
00:17:38,700 --> 00:17:55,420
So genes can be, let's say,
100 to ten to the fifth

248
00:17:55,420 --> 00:17:59,600
nucleotides long.

249
00:17:59,600 --> 00:18:02,330
And so the number of
possibilities is really

250
00:18:02,330 --> 00:18:03,420
extraordinary.

251
00:18:03,420 --> 00:18:06,500
And it's one of the reasons
that all of life can be

252
00:18:06,500 --> 00:18:08,335
encoded in nucleic acids.

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00:18:15,110 --> 00:18:16,960
And the last thing that
I want to tell you

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about nucleic acids--

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00:18:20,010 --> 00:18:23,220
which will become and will
remain one of the most

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00:18:23,220 --> 00:18:25,960
important things you learn
in this class--

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is that DNA is usually
double stranded.

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00:18:29,220 --> 00:18:33,180
RNA is too, but it's really
DNA that uses this in an

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00:18:33,180 --> 00:18:36,085
extraordinarily important way.

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00:18:36,085 --> 00:18:42,480
So DNA is usually
double stranded.

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00:18:46,300 --> 00:18:47,550
What does that mean?

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00:18:52,700 --> 00:18:55,760
It gets to be double
stranded via

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00:18:55,760 --> 00:18:57,420
something called base pairing--

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00:19:03,410 --> 00:19:07,240
you'll see what this
means in a moment--

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which also means, or there's
another term that's used,

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which is complementarity,
as you will see.

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00:19:19,100 --> 00:19:21,430
And this double strandedness
does not

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00:19:21,430 --> 00:19:22,890
involve covalent bonds.

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00:19:22,890 --> 00:19:26,230
It involves that special type
of bonds that we discussed

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00:19:26,230 --> 00:19:28,765
last time, which are
the hydrogen bonds.

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00:19:31,910 --> 00:19:35,400
And there are rules
about this.

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Adenine will form two hydrogen
bonds with thymine or uracil.

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00:19:43,410 --> 00:19:48,520
Guanine forms three hydrogen
bonds with cytosine.

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00:19:48,520 --> 00:19:52,110
And that is a rule that is one
of the most important rules in

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nucleic acids.

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00:19:57,460 --> 00:20:01,380
From your book, here is a
picture of the two bases,

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adenine and thymine, that can
be lain opposite one another

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00:20:07,360 --> 00:20:11,990
such that these dotted lines
are hydrogen bonds between

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00:20:11,990 --> 00:20:15,120
oxygen and hydrogen or nitrogen
and hydrogen--

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00:20:15,120 --> 00:20:17,805
and the same kind of thing
for guanine and cytosine.

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00:20:17,805 --> 00:20:20,500
You don't need to know these
structures, exactly, but you

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do need to know base pairing
inside, outside, and

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00:20:24,440 --> 00:20:25,550
never forget it.

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00:20:25,550 --> 00:20:26,800
Okay.

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00:20:28,780 --> 00:20:30,970
Why is this important?

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00:20:30,970 --> 00:20:32,640
I'll tell you why this
is important.

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00:20:32,640 --> 00:20:35,960
It's important for DNA
replication and for the

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00:20:35,960 --> 00:20:38,950
passage of hereditary
information from one

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00:20:38,950 --> 00:20:41,270
generation to the next.

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00:20:41,270 --> 00:20:52,070
So, in DNA replication, the
idea is to pass genes on,

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00:20:52,070 --> 00:20:55,620
unperturbed, in the same
sequence from one generation

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00:20:55,620 --> 00:20:59,640
to the next at every
cell division.

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00:20:59,640 --> 00:21:07,720
So let's just, for instance,
start with a polymer here.

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00:21:07,720 --> 00:21:10,920
Ah, and something else that I
needed to tell you, which I

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00:21:10,920 --> 00:21:16,160
will in a second, is that when
nucleic acids form double

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00:21:16,160 --> 00:21:20,810
stranded structure, one strand
of nucleic acid--

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00:21:20,810 --> 00:21:22,110
my one arm--

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00:21:22,110 --> 00:21:25,630
will form a double stranded
structure with another strand

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00:21:25,630 --> 00:21:28,310
of nucleic acids, like so.

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00:21:28,310 --> 00:21:29,030
Okay.

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00:21:29,030 --> 00:21:30,560
That's what's referred
to up there.

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00:21:30,560 --> 00:21:33,010
The adenine's on one polymer.

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00:21:33,010 --> 00:21:35,080
The thymine is on
another polymer.

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00:21:35,080 --> 00:21:39,180
When these polymers form, they
form in what's called an

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00:21:39,180 --> 00:21:40,770
anti-parallel direction.

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00:21:40,770 --> 00:21:42,280
It's really hard to do.

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00:21:42,280 --> 00:21:46,890
But if this is my five prime end
and three prime end, the

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00:21:46,890 --> 00:21:50,450
five prime end of one and the
will be opposite the three

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00:21:50,450 --> 00:21:51,690
prime end of another strand.

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00:21:51,690 --> 00:21:52,880
I guess I can do it this way--

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00:21:52,880 --> 00:21:54,130
topologically easier.

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00:21:56,680 --> 00:21:57,290
Okay--

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00:21:57,290 --> 00:22:01,120
so five prime opposite three
prime, five prime opposite

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00:22:01,120 --> 00:22:02,770
three prime.

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00:22:02,770 --> 00:22:07,310
So let's draw the complement
of this for

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00:22:07,310 --> 00:22:09,350
the nucleotide polymer.

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00:22:09,350 --> 00:22:15,100
There'll be thymine, cytosine,
adenine, thymine.

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00:22:15,100 --> 00:22:18,420
And look what I've done to the
five primes and three prime.

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00:22:18,420 --> 00:22:22,730
Means they are one five prime
opposite a three prime, and

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00:22:22,730 --> 00:22:25,630
the other three prime opposite
a five prime.

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00:22:25,630 --> 00:22:32,200
This arrangement called an
anti-parallel arrangement of

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00:22:32,200 --> 00:22:33,710
nucleic acids.

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00:22:33,710 --> 00:22:37,140
And it is super important that
you never forget this.

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00:22:37,140 --> 00:22:42,390
During DNA replication, the
strands of this double

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00:22:42,390 --> 00:22:45,060
stranded polymer separate.

326
00:22:54,120 --> 00:23:00,350
And so you have five prime
AGTA three prime--

327
00:23:00,350 --> 00:23:01,760
is one strand--

328
00:23:01,760 --> 00:23:09,740
plus three prime TCAT five
prime-- two single strands.

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00:23:09,740 --> 00:23:13,460
And here's the magic, and this
is what Watson and Crick got

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00:23:13,460 --> 00:23:18,080
the Nobel Prize for long ago
for understanding that when

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00:23:18,080 --> 00:23:22,330
DNA replicates, those strands
get filled in.

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00:23:22,330 --> 00:23:29,820
So this five prime AGTA three
prime will now get synthesized

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00:23:29,820 --> 00:23:33,000
opposite its complement--

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00:23:33,000 --> 00:23:39,800
three prime of TCAT five
prime plus this guy--

335
00:23:39,800 --> 00:23:48,420
three prime TCAT five prime will
get its complement made.

336
00:23:48,420 --> 00:23:50,600
And look what you have got.

337
00:23:50,600 --> 00:23:54,540
You have started with one
strand, one double stranded

338
00:23:54,540 --> 00:24:00,000
moiety, and you've landed up
with two identical replicas of

339
00:24:00,000 --> 00:24:01,495
what you started with--

340
00:24:01,495 --> 00:24:03,645
so two identical replicates.

341
00:24:08,140 --> 00:24:11,980
That's redundant, but it really
pushes the point home--

342
00:24:11,980 --> 00:24:18,230
two identical replicates of this
parent molecule that we

343
00:24:18,230 --> 00:24:19,170
started with.

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00:24:19,170 --> 00:24:21,700
We'll have a lot more to say
about this when we spend a

345
00:24:21,700 --> 00:24:24,430
whole lecture on DNA
replication, but you should

346
00:24:24,430 --> 00:24:29,160
understand that this is one of
the profound natures of DNA as

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00:24:29,160 --> 00:24:30,410
the hereditary information.

348
00:24:34,030 --> 00:24:37,270
And from your book-- double
stranded DNA.

349
00:24:37,270 --> 00:24:41,040
We'll have more to say about
this, but double stranded DNA,

350
00:24:41,040 --> 00:24:44,450
because of chemical
considerations, goes into its

351
00:24:44,450 --> 00:24:47,980
most stable chemical state,
which is this very beautiful

352
00:24:47,980 --> 00:24:53,250
double helix that has structure
and is able to pack

353
00:24:53,250 --> 00:24:56,390
very tightly so that you
can get lots of genetic

354
00:24:56,390 --> 00:24:57,860
information in one cell.

355
00:25:02,300 --> 00:25:04,110
Last thing about
nucleic acids--

356
00:25:04,110 --> 00:25:08,940
RNA is often single stranded,
but it can also form

357
00:25:08,940 --> 00:25:11,770
structures that are partially
double stranded.

358
00:25:11,770 --> 00:25:15,040
And this is one such RNA
that's formed this very

359
00:25:15,040 --> 00:25:17,610
complicated, partially double
stranded molecule.