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Background research

I am aware that DNA polymerase works in pairs, at least. This is to process both opposite stands of a given chromosome. The 3'-to-5' "leading strand", and 5'-to-3' "lagging strand" simultaneously. This two-DNA-polymerase process is beautifully shown in this TED talk by Drew Berry.

I have not checked any non-online sources but simple Google queries failed to answer my questions below.

Question

Within a single Eukaryotic cell, is the process of DNA-replication carried out by just a single pair of DNA-polymerases? Or do multiple pairs of DNA-polymerases work in parallel?

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In the (beautifully rendered) video you linked to, the green molecules are DNA polymerases. So you can already see that there are more than two DNA polymerases at work!

At each replication fork, there is generally one DNA polymerase working on the leading strand, but on the lagging strand, multiple DNA polymerases may be working at the same time (as depicted in the video). Note that different types of polymerase are thought to be primarily responsible for the leading (Pol ε) and lagging (Pol δ) strands in eukaryotes (but not prokaryotes, which use Pol III for both).

Next, note that at every origin of replication, there are two replication forks working simultaneously, one in each direction. So that's double the number of polymerase molecules.

On top of that, a single eukaryotic cell has multiple chromosomes. Each one must have at least one origin of replication of its own, which can operate in parallel. In reality, each eukaryotic chromosome has up to thousands of origins of replication (prokaryotic chromosomes generally only have one). Human cells have on the order of 100,000 origins of replication. So depending on how many origins are active simultaneously, there are likely many thousands of polymerase molecules acting at once to replicate the DNA of a single eukaryotic cell.

You could probably do a rough estimate of the number of polymerase molecules active simultaneously by taking the average duration of S phase in your cell of interest and dividing by the genome size and the speed of polymerase.

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  • $\begingroup$ Never be too trusting of pretty pictures (/videos), there being multiple DNApol in the video could have been precisely why I asked the question in the first place (to check it's accuracy) $\endgroup$ – hello_there_andy Mar 14 '17 at 16:03
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    $\begingroup$ Fair point! But after checking the math, I trust that they did get that detail right in the video. $\endgroup$ – leekaiinthesky Mar 14 '17 at 17:26

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