DNA Structure and Replication

ID #1112

Are telomeres on both the leading and lagging strand, or just important to Okazaki fragments? The book confused me a little.


To be honest, thinking about telomeres in the context of DNA replication goes beyond what we're going to do in our class. So you can just leave our discussion about telomeres at the level we went over in lecture. But if you're reading about them in the book, let me mention that the leading strand isn't an issue for the ends of a linear chromosome -- the polymerase just goes until it runs out of template DNA and literally falls off. But the lagging strand is another issue. What I'm about to write probably won't make much sense on the date that slide was shown, but hopefully by next week if you read this again, it should make more sense. There's no problem laying down the primer right up to the end of the linear molecule on the lagging strand, but eventually that primer has to be removed and replaced with DNA nucleotides. And since the inclusion of "fresh" dNTPs depends on a 3'-OH group from a nucleotide further up, there's nothing to add the first "replacement" nucleotide to, since that primer was already at the end of the molecule. So that section can't be replicated, and the chromosome shortens by however many bases were between the end of the molecule and the end of the last primer added in and removed.

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