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What do they mean by, "bacterial dna has a single origin of replication?"

Discussion in 'MCAT Study Question Q&A' started by Gauss44, Sep 7, 2014.

  1. Gauss44

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    What do they mean by, "bacterial dna has a single origin of replication?"

    Do they mean that a maximum of one replication fork can exist at any given time?
     
  2. Cawolf

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    There is one site where DNA replication can start, but as far as I know, multiple rounds of replication can occur simultaneously still (or else it would be quite slow!).
     
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  3. Gandyy

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    Isnt that in eukaryotes though? ^ Not sure
     
  4. OP
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    Gauss44

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    Eukaryotes can definitely have multiple replication bubbles. I'm not sure about prokaryotes, and I'm not sure how "origins of replication" play into this (for eukaryotes or prokaryotes beyond what was said above, if correct).
     
  5. pacer

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    Origin of replication is where the process of replication can start to occur. This is the point on the chromosome where helicases would start to unwind the DNA, primases will add primers. Prokaryotes like bacteria have only 1 origin of replication but I don't think that you can apply the idea of a replication fork here becasue it is a single ds circular DNA that undergoes theta replication. You don't need to know the details of theta replication for the MCAT but just know that it is different than what eukaryotes go through.
     
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    Gauss44

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    So basically one dna polymerase could start replicating dna at the origin of replication and once that polymerase has moved down the dna a ways, another dna polymerase could start at that same origin of replication, then a third, then a fourth, etc.?
     
  7. GoldenTuth

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    Origin of replication has nothing to do with the replication fork. It's literally called "Origin" meaning that's where replication originates. When it originated it creates 2 forks with 4 DNA polymerases that are creating complementary strands to the separated DNA.

    Before the DNA replicates completely, the already replicated region of "origin of replication" can start replicating again even though the original replication wasn't completed yet.
     
  8. kraskadva

    kraskadva ...
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    To the bolded above, no. There are a lot of accessory proteins that regulate this very carefully so that DNA replication happens only once. I won't go into details since they're not necessary for the MCAT, just know that replication only happens once per division cycle. Otherwise things would get very screwy.
    More info here if you really want to know.

    Prokaryotes: have 1 origin of replication on the 1 circular chromosome and 1 on each plasmid, replication starts here on the circular chromosome, the DNA is unwound and there are 2 replication forks going in opposite directions.

    Eukaryotes: have multiple origins of replications on each linear chromosome, each oriR gives rise to 2 replication forks moving in opposite directions, when replication forks run into each other the strands are ligated just like Okazaki fragments and the DNApol floats off.

    You can have multiple transcription or translation happening, but not DNA replication.
     
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  9. GoldenTuth

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    I'm afraid I was wrong :( what I was talking about was eukaryotic cell, oh shame on me, I'm sorry guy!
     

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