DNA replication and % of original DNA

[joonkimdds]

if DNA undergoes 4 rounds of replication, what % of double stranded DNA produced contain part of the original?

100->50->25->12.5->6.25%

so I think answer should be 6.25% but the correct answer is 12.5%

help plz~!!


P.S. this question is from destroyer. My kaplan blue book also has the exact same question but Kaplan says it's 6.25%

I think the difference is that destroyer starts from single strand of DNA, wheras Kaplan starts from double strand of DNA.

How do we know how many strand of DNA we start with? Aren't DNA supposed to be always double strand?

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[nze82]

if DNA undergoes 4 rounds of replication, what % of double stranded DNA produced contain part of the original?

100->50->25->12.5->6.25%

so I think answer should be 6.25% but the correct answer is 12.5%

help plz~!!

After 4 rounds of replication you have 2^4 = 16 DNA strands, only 2 of which are from the original parent (Remember that DNA replication is semiconservative). So, the % of DNA containing the parental strand is:

2/16 = 0.125 = 12.5%

 

[joonkimdds]

After 4 rounds of replication you have 2^4 = 16 DNA strands, only 2 of which are from the original parent (Remember that DNA replication is semiconservative). So, the % of DNA containing the parental strand is:

2/16 = 0.125 = 12.5%

we start with 2 strands
becomes 4 after 1st round
becomes 8 after 2nd round
becomes 16 after 3rd round
becomes 32 after 4th round

so shouldn't it be 2/32 = 6.25%?

 

[pbure9]

Like you said both are right.

I've seen that kaplan question thrown around before.. it's just percent of original DNA from ALL the DNA after 4 rounds of replication, which includes the all single strands (2/32)

Whereas, as nze showed, in destroyer, its percent of original DNA from all double stranded DNA molecules after 4 rounds of replication (2/16)

 

[joonkimdds]

Like you said both are right.

I've seen that kaplan question thrown around before.. it's just percent of original DNA from ALL the DNA after 4 rounds of replication, which includes the all single strands (2/32)

Whereas, as nze showed, in destroyer, its percent of original DNA from all double stranded DNA molecules after 4 rounds of replication (2/16)

does the word u bolded really affect the answer? i mean aren't DNA always double stranded?

 

[nze82]

we start with 2 strands
becomes 4 after 1st round
becomes 8 after 2nd round
becomes 16 after 3rd round
becomes 32 after 4th round

so shouldn't it be 2/32 = 6.25%?

Hopefully, the following figure will clarify things for you:

As you can see, there are clearly 16 DNA molecules, and only two strands that are black (Original). Hence:
2/16 = 12.5%

 

[Streetwolf]

It says what % of the double stranded DNA *CONTAINS* an original DNA strand.

You can see from the above poster that of the 16 double stranded DNA formed, 2 of them contain a piece of the original DNA.

The way you are doing it is to consider every single strand (32 of them) and how many came from the original (2). That's not what the problem asks.

 

[nze82]

It says what % of the double stranded DNA *CONTAINS* an original DNA strand.

You can see from the above poster that of the 16 double stranded DNA formed, 2 of them contain a piece of the original DNA.

The way you are doing it is to consider every single strand (32 of them) and how many came from the original (2). That's not what the problem asks.

To OP: So, putting the word "double" in bold does in fact make a difference in the final answer!

 

[joonkimdds]

I get it now~ so when it specifically says double stranded, we got total of 16 double stranded DNA and 2 of them have original thus 2/16.

kaplan says "what % of the total DNA present would be comprised of the original DNA molecule". In this case, do we assume that DNA is single stranded thus double stranded DNA count as 2 separate DNA?

 

[pbure9]

I get it now~ so when it specifically says double stranded, we got total of 16 double stranded DNA and 2 of them have original thus 2/16.

kaplan says "what % of the total DNA present would be comprised of the original DNA molecule". In this case, do we assume that DNA is single stranded thus double stranded DNA count as 2 separate DNA?

lol yea more or less. thats the effect i was trying to acheive by bolding the double. Personally, I like the destroyer version of the question more for reasons that had you confused, whereas Kaplan was talking about the total strands of DNA

To OP: So, putting the word "double" in bold does in fact make a difference in the final answer!

success!

 

[joonkimdds]

lol yea more or less. thats the effect i was trying to acheive by bolding the double. Personally, I like the destroyer version of the question more for reasons that had you confused, whereas Kaplan was talking about the total strands of DNA



success!

If a question says we got a double stranded DNA. How many DNA are there?
In this case, is the answer 2?

 

[pbure9]

I'd say thats 2 strands of DNA and 1 DNA double helix.

So going back to the question.. thats 32 strands of DNA with 2 being original strands.

And that's 16 DNA double helices, 2 of which contain the original DNA.