cell cycle & post-replication repiar

[SaintJude]

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Post replication repair is used to repair double strand breaks in DNA. At what point in the cell cycle would a DNA double strand break, if left unrepaired, affect both chromatids in a pair of sister chromatids?

A. G-0 B.) G-1 C.) G-2 D.) M

EDIT: Answer is B. ) G-1

Can someone explain the answer? (not by POE!)

I personally included the picture as a reference. Edit: Changed pictures, see later post reason

 

[Temperature101]

Post replication repair is used to repair double strand breaks in DNA. At what point in the cell cycle would a DNA double strand break, if left unrepaired, affect both chromatids in a pair of sister chromatids?

A. G-0 B.) G-1 C.) G-2 D.) M

Can someone explain the answer? (not by POE!)

I personally included the picture as a reference.

What is the answer? Is it C...that is the answer that seems to make sense because after S phase which is replication of DNA, the cell enter G2 for more "growth" and preparation for mitosis...I would make sense for the chromatids to be affected if not repaired during the S phase.

 

[chiddler]

I think it's G2? G2 is after the synthesis phase so if the damage makes it past synthesis, then the chromosomes have replicated and both sister chromatids will be affected.

But I can't make up my mind why it cannot be M phase besides that this is a trick question lol

 

[SaintJude]

I said C as well, but that was wrong. It's B.) G1?! I don't know why.

Regardless, I think this question is good b/c it's exposing my cursory understanding of the cell-cycle.

 

[Temperature101]

I said C as well, but that was wrong. It's B.) G1?! I don't know why.

Regardless, I think this question is good b/c it's exposing my cursory understanding of the cell-cycle.

What is the explanation for G1?

 

[Danlee07]

Phases aren't all completely separated, so replication does not only occur in S phase. But the majority goes on in S phase because there was a whole G1 phase that dedicated to the preparation of the DNA synthesis.

In yeast, G1 phase has the necessary proteins in a licensing system factor that provides helicase-functioning MCM proteins, cdt-1, and cdc-6 which all bind on the origin replication complex. These proteins will allow for replication. But G2 phase doesn't have MCM proteins loaded, so there's no helicase for replication to occur; there's also an inactive licensing system in G2 so no additional chances for a helicase to be added and continue on to replication. This is also why the diagram says "Cells that cease division" in G1 and not any other phase.

I don't think this level of detail is required, but just know that there is a licensing system with necessary proteins for replication in G1 but not G2.

 

[ljc]

I might be misreading this, but I think all they're asking is essentially when does DNA duplicate.

Assume there is an error in the DNA (G1). That DNA is then duplicated (S). That DNA is passed onto both sister chromatids, and thus onto both daughter cells (M). If this error occurred any later than G1, it would only affect one of the chromatids and not the other (because they had already duplicated)

 

[qtsjoe]

I might be misreading this, but I think all they're asking is essentially when does DNA duplicate.

Assume there is an error in the DNA (G1). That DNA is then duplicated (S). That DNA is passed onto both sister chromatids, and thus onto both daughter cells (M). If this error occurred any later than G1, it would only affect one of the chromatids and not the other (because they had already duplicated)

I feel the same reasoning too, If it occurred during G2 it would only happen to one chromatid. The question is asking to the extent of both.

 

[SaintJude]

Yes, ljc.Thanks for making me see the light! I'm adding this picture, because it shows exactly what you are referring to. In order for the error to affect both sister chromatids, it has to occur before synthesis. Because it's during the S phase that the mutation would duplicated on its sister chromatid.
If the mutation occurred after S phase, it wouldn't have a chance to pass the mutation on to the sister chromatid