#of replication, and percent of original DNA molecules

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wkawk2416

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Okay, I was doing kaplan midterm exams, and i must say it was tough, wordy, and confusing. BTW i found some confusing question

kaplan midterm biology # 7

If a DNA molecule were to replicate itself three times, what percent of the total DNA present would be comprised of the original DNA molecule?

destoyer # 237

what percent of the double stranded DNA produced contains part of the original stranded DNA?

Please explain!
BTW i missed 6 questions out of 40 questions on kaplan midterm exam. is this test comparable to the actual DAT?
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wkawk2416 said:
Okay, I was doing kaplan midterm exams, and i must say it was tough, wordy, and confusing. BTW i found some confusing question

kaplan midterm biology # 7

If a DNA molecule were to replicate itself three times, what percent of the total DNA present would be comprised of the original DNA molecule?

destoyer # 237

what percent of the double stranded DNA produced contains part of the original stranded DNA?

Please explain!
BTW i missed 6 questions out of 40 questions on kaplan midterm exam. is this test comparable to the actual DAT?
Click to expand...
Every time you replicate DNA you get 2 new DNA and 1 strand of each DNA is composed of the parent strand. So after 3 rounds of replication....

1 --> 2 ---> 4 ---> 8

Out of these 8, 2 of them contain the parent strands. So 2/8 = 1/4 = 25%

Solve the same way for the destroyer question....
 
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Mstoothlady2012 said:
Every time you replicate DNA you get 2 new DNA and 1 strand of each DNA is composed of the parent strand. So after 3 rounds of replication....

1 --> 2 ---> 4 ---> 8

Out of these 8, 2 of them contain the parent strands. So 2/8 = 1/4 = 25%

Solve the same way for the destroyer question....
Click to expand...

For question one the total DNA present is 16 strands because each of the DNA molecules is double stranded. Therefore the answer is 2/16 or 1/8=12.5%
 
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For question 2 there are a total DNA double stranded molecules of 1>2>4>8>16. Out of those 16 2 have a copy of the original strand. Therefore the answer to that question is also 1/8=12.5%
 
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Use the equation (1/2)^n for how much DNA is the same as the original after n replication events. Remember: DNA replication is semi-conservative!
 
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What were the choices? After 3 replication cycles 8 DNA sets will be present in the form of 16 strands. Of the 8 DNA molecules only 2 will have any parent DNA left, and those 2 will be comprised of 50% parent DNA and 50% new DNA. So the answer is 2/8 = 25% if you are talking about a strand having ANY parent DNA left in it. If you are talking about a strand having ALL parent DNA left the answer will be zero. They are probably talking about the former, but I agree that the question is vague.
 
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Aceofspades said:
What were the choices? After 3 replication cycles 8 DNA sets will be present in the form of 16 strands. Of the 8 DNA molecules only 2 will have any parent DNA left, and those 2 will be comprised of 50% parent DNA and 50% new DNA. So the answer is 2/8 = 25% if you are talking about a strand having ANY parent DNA left in it. If you are talking about a strand having ALL parent DNA left the answer will be zero. They are probably talking about the former, but I agree that the question is vague.
Click to expand...
You are incorrect there would be 8 DNA molecules and each molecule has 2 strands. Therefore after 3divisions there are 2<4<8<16 strands. If 2 are from the original and there are 16 strands in total then it is 1/8=12.5%
 
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Thats what i said before just scroll up i explained both pretty clearly.
 
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so for second question,

the original DNA strand that was first copied to become double stranded DNA is considered as original molecules of DNA?
 
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wkawk2416 said:
so for second question,

the original DNA strand that was first copied to become double stranded DNA is considered as original molecules of DNA?
Click to expand...
For the second question there are two strands of DNA from the original Molecule. Now each of those strands make up half of a new DNA molecule. Therefore from the 16 new DNA molecules there are 2 that have an original strand.
2/16=12.5%

Hope this helped.
 
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