mitosis quesiton

[mgdent]

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The DNA of a bacteria is labeled with radioactive phosphate. Following mitosis, each daughter cell will have:
Answer- 1/2 the radioactivity of the parent.

I thought mitosis results in identical daughter cells so it would have the same radioactivity as the parent. Any thoughts?

 

[cm8a12321]

The DNA of a bacteria is labeled with radioactive phosphate. Following mitosis, each daughter cell will have:
Answer- 1/2 the radioactivity of the parent.

I thought mitosis results in identical daughter cells so it would have the same radioactivity as the parent. Any thoughts?

In a bacteria, the plasmid is double stranded. During mitosis, each of the strand is replicated at the origin of replication and undergoes PMAT.

When replication is complete and reached about twice its initial size, its plasma membrane grows inward, dividing into two daughter cells. Each inherit 1/2 of the radioactivity of the parent.

 

[nicolae]

This question seems to address DNA replication models. Bacterial (prokaryotic) chromosomes are circular, double stranded DNA, and they replicate by binary fission, whereas eukaryotic chromosomes are linear and double stranded, and they replicate by mitosis. The initial step in DNA replication is uncoiling of the DNA and replication by DNA polymerases begins (in prokaryotes) at origins of replication. Three possible models of chromosome replication are the:

A) Conservative: Parental strands serve as templates for daughter strands, and then parental strands realign. (One daughter 100% radioactive, one daughter 0% radioactive )

B) Semiconservative: Parental strands separate, and each serves as a template for daughter strand. (each of the two daughter strands would have 1 radioactive parental strand, one newly synthesized, nonradioactive strand)

C) Dispersive: Daughter strands are a mixture of parental and newly synthesized DNA. (both daughter strands would have alternating radioactive/nonradioactive nucleotides on both strands)

The 100% radioactively labeled parental DNA will be different from the newly synthesized nonradioactive nucleotides (more specifically phosphates in this case) of the daughter DNA. DNA replication does indeed follow the semi-conservative model (Meselson & Stahl experiment), and as such daughters will have 1 new strand (nonradioactive), and 1 parental strand, and thus only 1/2 radioactivity of the parent.

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"I thought mitosis results in identical daughter cells so it would have the same radioactivity as the parent. Any thoughts?"

Edit: Remember, enzymes generally cannot distinguish between different isotopes, in this case phosphate.



DAT T-MINUS 4 DAYS

 

[chromosome21]

great explanations everyone.

but to answer this question, all you need to know is mitosis. here, we have radioactive bacterial DNA. When it replicates, we will need new ATPs, GTPs, CTPs, TTPs and these are not radioactive. so the new strand will not be radioactive labeled. In short, you'd have half of the radioactive DNAs and half of normal DNAs in daughter cells.