BIO question on Kaplan

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pandalove89

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The DNA of a bacteria is labeled with a radioactive phosphate. Following mitosis, each daughter cell will have:

A. 1/4 the radioactivity of the parent
B. 1/2 the radioactivity of the parent
C. The same radioactivity as the parent
D. 2 times the radioactivity as the parent
E. It is not possible to determine

I was stuck on either choice B and C, but I chose C and got it wrong.

The right answer is B, and their explanation is something to do with semiconservative replication which I understand, but don't bacteria use asexual reproduction and therefore have the exact DNA structure of their parent?

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It is asexual reproduction but what you're missing is that before the bacteria cell split into 2 daughter cells, it has to go through replication first. And as you mentioned replication of bacteria could be semiconservative, therefore each daughter cell would have only 1/2 of the radioactivity of the 'mother' bacteria. Meaning, the double strand DNA of each daughter cell contains 1 strand of the labeled DNA and 1 strand of newly synthesized DNA (via replication).
 
It is asexual reproduction but what you're missing is that before the bacteria cell split into 2 daughter cells, it has to go through replication first. And as you mentioned replication of bacteria could be semiconservative, therefore each daughter cell would have only 1/2 of the radioactivity of the 'mother' bacteria. Meaning, the double strand DNA of each daughter cell contains 1 strand of the labeled DNA and 1 strand of newly synthesized DNA (via replication).



but if it's asexual then where would the other "daughter" strand come from? There's only one "parent" in this case
 
but if it's asexual then where would the other "daughter" strand come from? There's only one "parent" in this case

i thought bacteria only reproduce through binary fission? what pooyah is saying makes sense if it was mitosis, but bacteria don't have a nucleus - how do they do mitosis? and bacteria have a single circular strand of DNA... the idea of being semi-conservative shouldn't have to do with anything...

confused... anyone else?
 
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Ignore the wording of "mitosis" in the question. It's a typo. They're really asking: after replication, how much of the daughter DNA (btw, why can't it be a son???) is composed of the original DNA?

The answer would be 1/2. If the original DNA strands were A1A2, then the daughter DNA strands would be A1B1 and A2B2. Thus each one is 1/2 new DNA and 1/2 original DNA.

Btw, bacteria is double stranded. If you a google image search on 'bacteria dna replication' you'll see what I mean in the third photo.
 
Ignore the wording of "mitosis" in the question. It's a typo. They're really asking: after replication, how much of the daughter DNA (btw, why can't it be a son???) is composed of the original DNA?

The answer would be 1/2. If the original DNA strands were A1A2, then the daughter DNA strands would be A1B1 and A2B2. Thus each one is 1/2 new DNA and 1/2 original DNA.

Btw, bacteria is double stranded. If you a google image search on 'bacteria dna replication' you'll see what I mean in the third photo.


ahh... my bad, it is double stranded. confused "single circular dna" with single stranded circular dna. thanks.

and, i'm fine with it being a daughter... ;)
 
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