00:04
Several enzymes participate in the replication of the main chromosome in e.
00:10
Coli.
00:11
So this is the dna replication process.
00:13
During elongation of dna, at a replication fork, will be unwind by the enzyme helicase.
00:21
So helicase goes into the first blank.
00:24
This is the enzyme that unwinds the double -stranded dna.
00:46
Now the next blank, in front of the replication fork, the diploid mesomerase, this is a class ii, it will cut both strands of dna, relieving the tension of the nearby unwinding.
01:25
Now once you have the dna unwind, and then it forms a replication bubble.
01:31
At a given origin of replication, we find actually two replication forks with both a leading strand and a lagging strand.
01:39
So i'm going to draw.
01:41
So if you have helicase to unwind dna, and class ii diploid mesomerase to cut both strands of dna, you will actually have a replication bubble like this.
01:54
And then you have a single origin of replication, and then you have two replication forks.
02:10
So they are moving away from the origin of replication.
02:13
So in the replication bubble, you have two strands of dna, which replicate both strands of dna.
02:22
One is called a leading strand.
02:28
This is being synthesized continuously.
02:31
And the other strand, we call it lagging strand.
02:43
So now the leading strand goes into the window blank.
02:48
Now the next part of the question focuses on the lagging strand, which is on the bottom.
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The lagging strand is also called discontinuous strand, because it is synthesized in many small pieces.
03:22
So we can see that each arrow represents one small fragment.
03:26
So this is synthesized discontinuously.
03:29
And the top strand, leading strand, as you can see, you have one long line with one arrow.
03:35
This is synthesized continuously.
03:38
Now the next part, each of these small fragments needs its own primer, which will be deposited by the enzyme primase.
03:45
So as you can see, in the beginning of each small fragment, you have a red fragment.
03:50
This is called the primers.
03:52
And the primers are being added by enzyme primase.
03:56
As you can see, that primase put down the red primer.
04:00
These are single -stranded rna fragments.
04:06
So each primer is elongated by the enzyme, which is called the dna polymerase iii, which add nucleotide to its three prime end.
04:19
So as you can see, that usually the primer is the five prime end and it goes towards three prime end.
04:28
So the enzyme that does this job, we call this dna polymerase number three.
04:40
As you can see that all the new strand is being added at the three prime end of the primer.
04:49
So dna polymerase iii can only add the new nucleotide at the three prime end of the primer.
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All right, next blank.
05:03
So one such fragment that include a primer and a dna nucleotide added to it is called a, the name of each of those fragment, we call this okazaki fragment.
05:22
So on the figure, you can see three okazaki fragments, each with a piece of primer and a dna.
05:32
So each individual fragment on the ligand strand grows towards, as if you can see the arrow, it towards the origin of a replication.
05:44
So you can see the origin of replication is in the middle and then the arrow is also towards the origin of replication.
05:50
So as you can see, since the replication fork has a arrow moves away from original replication, which is towards right side.
05:59
So this means that each individual fragment on a ligand strand does grows away from the replication fork...