Replication forks and functionality

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In summary, the question asks what would happen if a mutant with only one functional fork per replication bubble arose during DNA replication. The correct answer is d, as the replication process would take twice as long in this scenario. This applies to both prokaryotic and eukaryotic DNA replication. However, there may be some leftover DNA that cannot be replicated due to the lack of functional forks, and this is more likely to occur in eukaryotic DNA replication due to multiple origins of replication. The context of the question implies prokaryotic DNA replication, but it could also apply to eukaryotic replication.
  • #1
PoisonCupcake
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Hi! Was hoping I could get someone to explain this question to me..having some trouble with it...

"At each origin of replication, DNA synthesis proceeds bidirectionally from two replication forks. Which of the following would happen if a mutant arose having only one functional fork per replication bubble?

a.No change at all in replication
b. Replication would take place only on one half of the chromosome
c. Replication would be complete only on the leading strand
d. replication would take twice as long"

The answer is d, which definitely makes sense to me if this was prokaryotic DNA (ie. circular).. but I don't understand how the entire chromosome could be replicated if this was linear DNA like in most eukaryotes. Wouldn't only half of each parental strand be replicated since, for example, there isn't even a replisome traveling in the other direction to get rid of hydrogen bonds?

Thanks for your input in advance :)
 
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  • #2
PoisonCupcake said:
Hi! Was hoping I could get someone to explain this question to me..having some trouble with it...

"At each origin of replication, DNA synthesis proceeds bidirectionally from two replication forks. Which of the following would happen if a mutant arose having only one functional fork per replication bubble?

a.No change at all in replication
b. Replication would take place only on one half of the chromosome
c. Replication would be complete only on the leading strand
d. replication would take twice as long"

The answer is d, which definitely makes sense to me if this was prokaryotic DNA (ie. circular).. but I don't understand how the entire chromosome could be replicated if this was linear DNA like in most eukaryotes. Wouldn't only half of each parental strand be replicated since, for example, there isn't even a replisome traveling in the other direction to get rid of hydrogen bonds?

Thanks for your input in advance :)

The context probably implies prokaryotic DNA replication. Where was this question taken from?
 
  • #3
mishrashubham said:
The context probably implies prokaryotic DNA replication. Where was this question taken from?

It's from a textbook called "Introduction to Genetic Analysis". That's the whole of the question though, and that chapter discusses both prokaryotic and eukaryotic replication. The book is full of badly written questions in my opinion though.. so maybe this is just a factor of that.

So you agree the that this fits for prokaryotic replication only?
 
  • #4
The answer (d) fits with eukaryotic DNA replication as well. Remember that in eukaryotes, there are multiple origins of replication, in contrast to prokaryotes which rely on only one origin.
 
  • #5
But even so wouldn't there be a little bit that couldn't be replicated? Say you have 3 bubbles, all going right. Most of the chromosome could be replicated, but wouldn't there be a tiny bit to the left of the leftmost replication bubble that couldn't be done?

E: When it says one functional fork in the bubbles I assume they'd all either go left or right. Maybe some can go right or some can go left in the question??
 
  • #6
DNA is pretty symmetric, so how would a replisome know which direction is right and which direction is left?
 
  • #7
PoisonCupcake said:
But even so wouldn't there be a little bit that couldn't be replicated? Say you have 3 bubbles, all going right. Most of the chromosome could be replicated, but wouldn't there be a tiny bit to the left of the leftmost replication bubble that couldn't be done?

E: When it says one functional fork in the bubbles I assume they'd all either go left or right. Maybe some can go right or some can go left in the question??

The chance of all going in one direction is small. However that still leaves the problem of leftover DNA. All you need are two diverging forks or one at the end which does not open up to the periphery like you said.
 

1. What is a replication fork?

A replication fork is a structure that forms during DNA replication, where the double helix of DNA is unwound and separated into two single strands. This allows for the replication of the DNA by adding complementary nucleotides to each of the original strands.

2. How does a replication fork function?

A replication fork functions by using enzymes called DNA polymerases to add complementary nucleotides to each of the original strands. These nucleotides are added in a specific sequence, following the base pairing rules of A-T and C-G. The replication fork also has other proteins that help to stabilize the unwound DNA and prevent the strands from rejoining prematurely.

3. What happens if the replication fork encounters a damaged DNA base?

If the replication fork encounters a damaged DNA base, it can be repaired by specialized enzymes before the DNA replication process continues. If the damage is too extensive, the replication fork may stall or collapse, leading to errors in the replicated DNA.

4. What is the role of topoisomerases in replication fork functionality?

Topoisomerases are enzymes that help to relieve the tension that builds up as the DNA strands are unwound and replicated. They do this by creating temporary breaks in the DNA and allowing the strands to rotate, which prevents the DNA from becoming tangled.

5. How does the direction of DNA replication differ on the leading and lagging strands at the replication fork?

The leading strand is replicated continuously in the same direction as the replication fork moves, while the lagging strand is replicated in short fragments called Okazaki fragments. These fragments are later joined together by enzymes to form a continuous strand. This difference in replication direction is due to the antiparallel nature of DNA, where one strand runs in the opposite direction of the other.

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