Typical DNA replication times

Question

Just out of curiosity (I am completely strange to biology), as I have been unable to find this info on the internet: How long does the whole DNA replication process take? (say, the replication of a whole chromosome) Approximately, how long does the DNA spend in a single helix structure during replication?

I am curious about the time scales of these processes, from the moment the polymerase starts cutting the double helix till the moment there are two double helices perfectly formed (one of them a copy of the other). How long can this take? miliseconds? seconds?

Answer 1

A mammalian cell takes about 8 hours to replicate all of its DNA in its S phase; a yeast cell would take about 40 minutes.

Some other information that you seem to not have quite the right information about:

1. The DNA polymerase does not unwind/split the DNA—that is the job of DNA helicase. The DNA polymerase cannot bind to the single-stranded DNA until the helicase unwinds the double-stranded DNA ("melts"), or the dsDNA is artificially melted in a test tube via high temperature.

2. The dsDNA is not fully separated before it is copied. There are tens of thousands of sites—origins of replication—across the genome that unwind and begin replicating every time the cell replicates its genome.

"...DNA replication in most eukaryotic cells occurs only during a specific part of the cell-division cycle, called the DNA synthesis phase or S phase. In a mammalian cell, the S phase typically lasts for about 8 hours; in simpler eukaryotic cells such as yeasts, the S phase can be as short as 40 minutes."

"An average-size human chromosome contains a single linear DNA molecule of about 150 million nucleotide pairs. It would take (0.02 seconds/nucleotide) x (150e6 nucleotides) = 3e6 seconds (about 35 days) to replicate such a DNA molecule from end to end with a single replication fork."

"...Approximately 30,000–50,000 origins of replication are used each time a human cell divides."

–Molecular Biology of the Cell, 6e, Alberts, et al.

Answer 2

I think your view of DNA replication is a little off-target in relation to strand separation (which produces what you call “single helix structure”). The strands of the DNA are separated continually as replication occurs and then they are copied quite quickly by DNA polymerase. They are not separated completely and then copied. (And DNA polymerase doesn’t cut anything.)

But here are some typical times from on-line text books, where you can read more about the subject:

Bacterial cells

According to the text book The Molecular Biology of the Cell:

“It takes E. coli about 40 minutes to duplicate its genome of 4.6 × 10⁶ nucleotide pairs.”

And this has been discussed in an answer to a previous question.

Animal Cells

According to the text book, The Cell:

…human cells in culture, which divide approximately every 24 hours.

However, as explained out in the section cited, S phase — when DNA synthesis occurs — only takes about 8 hours. (Thanks to @rotaredom for pointing this out.)