Kaplan Bio Question

[Muggs]

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There is a similar question in Destroyer.

http://imgur.com/txl2j

wouldn't 3 rounds of replication amount to 8 total daughter strands of the original single DNA molecule (not 16)?

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

2/8 = 25%

so the answer would be E and not D?

am i missing something>

 

[Mr. Thirsty]

This confused me at first too, but I think of it like this.

You start out with 2 strands of the original DNA. After the first replication, each strand is attached to a new replicated strand. so there are 4 strands total after the first replication. Second replication: double it = 8. Third replication, double it = 16. Now there are still only the 2 strands in that 16 that you started with so it's 2/16 = 1/8 = 12.5%

Hope that helps.

 

[Muggs]

This confused me at first too, but I think of it like this.

You start out with 2 strands of the original DNA. After the first replication, each strand is attached to a new replicated strand. so there are 4 strands total after the first replication. Second replication: double it = 8. Third replication, double it = 16. Now there are still only the 2 strands in that 16 that you started with so it's 2/16 = 1/8 = 12.5%

Hope that helps.

so i was looking at the # of dna molecules produced after each replication, but I guess the question is asking for the number of strands?

 

[NDPitch]

I was always getting these mixed up as well. I understand it now. Whether or not you want to talk about it in terms of strands or not, the answer is the same. The % won't change. This is the way I think about it which usually gets me the right answer.

You start with 1 DNA molecule. This number will double after each reproduction. So...

1, 2, 4, 8, 16 - this would be 4 rounds of replication.

So after 4 rounds of replication, you have 16 DNA molecules that originated from your starting molecule. Now, as for what is the percentage of original DNA? This is where you have to account for the fact that the original DNA molecule split into two strands, and created 2 new molecules.

So, 16 molecules of DNA (from above) is actually 32 single strands of DNA. 2 of those 32 were the ones you started with. So in this example, your percentage would be 2/32, or 1/16.

 

[Mr. Thirsty]

Yeah for the percentage of original DNA it is asking about strands.

 

[joeeeey3]

just think of it as original DNA strand going thru half life decay

from 100% of original strand,
after first round of replication: 50%
2nd round: 25%
3rd round 12.5%

 

[Muggs]

I was always getting these mixed up as well. I understand it now. Whether or not you want to talk about it in terms of strands or not, the answer is the same. The % won't change. This is the way I think about it which usually gets me the right answer.

You start with 1 DNA molecule. This number will double after each reproduction. So...

1, 2, 4, 8, 16 - this would be 5 rounds of replication.

So after 5 rounds of replication, you have 16 DNA molecules that originated from your starting molecule. Now, as for what is the percentage of original DNA? This is where you have to account for the fact that the original DNA molecule split into two strands, and created 2 new molecules.

So, 16 molecules of DNA (from above) is actually 32 single strands of DNA. 2 of those 32 were the ones you started with. So in this example, your percentage would be 2/32, or 1/16.

wouldn't 3 replications then be ... 1, 2, 4?
so after 3 rounds of replication, you have 4 dna molecules --> 8 single strands, 2 of which contain original dna.

idk why i keep confusing myself...

 

[Muggs]

Yeah for the percentage of original DNA it is asking about strands.

the reason i'm confused is because bio destroyer #338 asks ...
Consider a sample of dna that undergoes 4 rounds of replication. What % of double stranded dna produced contains part of the original stranded dna?

the answer to the 4 replications is 12.5% in the solutions, which is the same answer as that given in my original post for 3 replications.

confused?

 

[NDPitch]

Haha nope. The first round doesn't leave you with 1 DNA molecule. It leaves you with 2.

So after 1 round of DNA replication, you go from 1 molecule of DNA, to 2 molecules.

Then you go from 2 molecules, to 4 molecules.

Then you go from 4 molecules, to 8 molecules.

8 molecules is 16 strands of DNA, 2 of which were the original.

2/16 = 1/8 = 12.5%

 

[NDPitch]

the reason i'm confused is because bio destroyer #338 asks ...
Consider a sample of dna that undergoes 4 rounds of replication. What % of double stranded dna produced contains part of the original stranded dna?

the answer to the 4 replications is 12.5% in the solutions, which is the same answer as that given in my original post for 3 replications.

confused?

Yeah I think that's an error. Just goes to show you even the creator of DAT destroyer can get confused with this, haha

 

[Muggs]

Haha nope. The first round doesn't leave you with 1 DNA molecule. It leaves you with 2.

So after 1 round of DNA replication, you go from 1 molecule of DNA, to 2 molecules.

Then you go from 2 molecules, to 4 molecules.

Then you go from 4 molecules, to 8 molecules.

8 molecules is 16 strands of DNA, 2 of which were the original.

2/16 = 1/8 = 12.5%

so then did you mean to say 4 rounds of replication rather than 5?

 

[NDPitch]

so then did you mean to say 4 rounds of replication rather than 5?

yes, I just edited my post to correct

 

[Toadesque]

just think of it as original DNA strand going thru half life decay

from 100% of original strand,
after first round of replication: 50%
2nd round: 25%
3rd round 12.5%

This is exactly how I think of it