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Replication forks and functionality

  1. Dec 10, 2011 #1
    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 :)
     
  2. jcsd
  3. Dec 11, 2011 #2
    The context probably implies prokaryotic DNA replication. Where was this question taken from?
     
  4. Dec 11, 2011 #3
    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?
     
  5. Dec 11, 2011 #4

    Ygggdrasil

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    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.
     
  6. Dec 11, 2011 #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??
     
  7. Dec 11, 2011 #6

    Ygggdrasil

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    DNA is pretty symmetric, so how would a replisome know which direction is right and which direction is left?
     
  8. Dec 11, 2011 #7
    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.
     
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