Week 06
Title: How long does DNA polymerase can replicate nucleotide at once?
Introduction
By using sequencing techniques, we can only sequence short fragment of DNA sequence. However, in our cell, whole DNA can be replicated by DNA polymerase only in 24 hours. Then, how many DNA nucleotides can be replicated by one DNA polymerase at once in eukaryotic cell? To figure out this, I did very simple calculation with entire DNA length of human and the number of replication origin.
Result
In eukaryotic cell, DNA replication occurs during S phase of cell cycle. The three steps of DNA replication is initiation, elongation and termination. Initiation begins with the unwinding of the double helix at a particular short sequence of nucleotides known as the origin of replication. The opening of these origins generates two Y-shaped areas called replication fork. During elongation DNA polymerase catalyzes the joining of a new nucleotide to the preceding nucleotide from 5’ to 3’.
So, we can calculate the number of nucleotides replicated by one DNA polymerase at once by dividing entire DNA length of human with the number of replication origin.
{(entire DNA length of human) / (number of replication origin)} / 2
The reason of why dividing by 2 is that in one replication origin, two DNA polymerases work in opposite direction.
The haploid human genome occupies a total of just over 3 billion DNA base pairs and 50,000 DNA replication origins are activated in one cell cycle. So, {3*1015/5*104}/2 = 30,000bp. The number of nucleotides replicated by one DNA polymerase at once is 30,000bp.
Discussion
The calculation for estimating the number of nucleotides replicated by one DNA polymerase at once is very simple, so there must be the other things that I should consider. Also, DNA polymerase of prokaryotic and eukaryotic are little bit different so it is good for thinking with prokaryotic cell next time.
Reference
https://www.ncbi.nlm.nih.gov/books/NBK9876/
http://www.igh.cnrs.fr/equip/mechali/publications/RevieworiginsNRCMB2010.pdf
Genetics, frome gene to genomes, 5th, Leland H.Hartwell, Michael L. Goldberg, 189-191
