bio question

[lilietta2000]

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Can somebody help me with this question please?


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. G0
B. G1
C. G2
D. M

 

[minhaj]

my guess would be M because the broken DNA could not be tightly packed into chromosomes and be properly divided among the daughter cells. Thats what I would choose. What is the answer?

 

[lilietta2000]

my guess would be M because the broken DNA could not be tightly packed into chromosomes and be properly divided among the daughter cells. Thats what I would choose. What is the answer?

The answr is actually G1 but why?

 

[minhaj]

i completely misread the question the first time around. i left out the sister chromatids part... to answer your question, DNA replication takes place in the S phase, which comes after the G1/G0 phase. If there is a break in the DNA double strand before the S phase, say in G1, then the break would be present in both sister chromatids after the replication in the S phase i.e. the break would be copied. however, if there is a break in the DNA after G1 phase, suppose in G2 or M phase, the break will not be present in both the sister chromatids. Only one of the chromatids will have it as replication of the DNA has already taken place in the S phase. G0 cannot be the answer because DNA replication does not occur in cells that enter G0 phase. I hope thats not too confusing.

 

[engineeredout]

That question seems confusing. By Minhaj's reasoning I'd expect the answer to be in the S phase, because its asking at what stage in the cycle would the sister chromatids be affected, which you would expect to be S because thats when DNA replicates.

 

[minhaj]

That question seems confusing. By Minhaj's reasoning I'd expect the answer to be in the S phase, because its asking at what stage in the cycle would the sister chromatids be affected, which you would expect to be S because thats when DNA replicates.

I agree it is a confusing question. It says in which phase would an unrepaired dna affect BOTH sister chromatids. Now if the break occurred in S phase while the DNA was replicating, then the break would not necessarily be present in BOTH the chromatids. However, if it occured in G1 phase, then the break would HAVE to present in both the chromatids. In other words, the template that is used for replicating would have the break. Hence, the break would have to be present in both the chromatids. Thats how I reasoned it anyways. 🙂

 

[engineeredout]

Makes sense. Still a ****ty question.

 

[seraph524]

Makes sense. Still a ****ty question.

The MCAT is a ****ty test.

 

[lilietta2000]

Yes, makes more sense now ,thanks!

 

[minhaj]

Makes sense. Still a ****ty question.

Totally agree. If you miss even a little bit of the question you get a completely different answer. Not reading the question correctly is gonna kill me on the mcat. Hell I even misread questions on the forum when I have ample time. MCAT is gonna be a bitch!

No problem, OP.

 

[Kaustikos]

Totally agree. If you miss even a little bit of the question you get a completely different answer. Not reading the question correctly is gonna kill me on the mcat. Hell I even misread questions on the forum when I have ample time. MCAT is gonna be a bitch!

No problem, OP.

It's not missing parts, persay, just terrible wording.

 

[AsuKa]

the question made sense to me. i did'nt think it was tricky or had terrible wording. guess i got lucky 🙂

i just drew out the cell cycle, and then reasoned that both sisters chromatids must be affected.

like minhaj said, it can't be g0.

and if the problem was after dna replication, then only 1 of the chromatids would have the problem, so it can't be g2 or m

so obviously it has to be before the dna is replicated, which is g1! now if they put in "s phase" as a choice, that could have been tricky