Density 100% 50% 50% 75% 88% 94% N14 N15 If the following...

Density 100% 50% 50% 75% 88% 94% N14 N15 If the following density profile (above) had been produced by the Meselson and Stahl experiment, what conclusion could have been drawn about DNA replication? Replication model cannot be determined from these results alone Replication is consistent with the conservative model Either conservative or semiconservative Replication is consistent with the semiconservative model Replication is consistent with the dispersive model

Transcript

00:01 So according to the density profile produced by methods under start, what conclusion can you have about dna replication? so looking at the profile, i would say that according to this profile, dna is going to pick up this conservative model.

00:19 According to conservative model, when you produce a dna replication, the old strand will stay together.

00:27 And then you will have new strand stay together.

00:31 So this is called conservative.

00:33 One strand is completely old.

00:35 One strand is completely new.

00:38 So now let's use drawing to figure out the first several rounds of this dna replication.

00:44 You start out with both strands of n15.

00:48 And then you move this single strand dna into a media that has n14.

00:53 So after first round of replication, you will produce, you have an old dna strand and they will stay together.

01:01 So you can see this is the old strand, which is made of n15.

01:05 Now, due to the dna replication, you'll produce two new strands.

01:09 And then they stay together as well as a single strand, as a double -stranded dna molecule, n14.

01:17 So this is completely old.

01:19 And this is completely new.

01:21 So you have one old and one new.

01:24 So this is why we have 50 % n14 and 50 % n15.

01:28 So it's a 50 % versus 50 % rate.

01:33 After another round of replication, again, the black will stay together and produce another copy of new double -stranded dna, which is made of n14.

01:49 And then you'll have the bottom n14, and then made another new strand of n14.

01:59 So you can see that three out of four will be n14 only.

02:02 This is 75%...

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