The Replication of DNA
07/11/2010 § 1 Comment
DNA needs to replicate with continuity and fidelity, meaning that it must copy without change. (That’s just a rule of life.)
Firstly, if we remember the structure of DNA, we can recall that the separate subunits are held together by covalent bonds and hydrogen bonds. The covalent bonds are strong enough to hold the phosphorus and sugar subunits together and the hydrogen bonds are also strong collectively (as a group of hydrogen bonds) but individually, can be unzipped easily. This enables the DNA molecules to be replicated easily, too. An enzyme called a DNA helicase is responsible for unwinding and unzipping the DNA. In this process, the helicase produces a replication fork, which is an area where the double helix has separated (replication forks are shaped as Y’s, like forks are). Both of a DNA molecule’s strands are copied at the same time by another enzyme called the DNA polymerase.
The polymerases use the open individual DNA strands as a template and add the complimentary nitrogen base to form a new strand. The enzymes continue to do this until the entire strand of DNA has been replicated. The product is two identical copies of DNA where each DNA molecule has one parent strand and one daughter strand each. This shows that DNA replicates semiconservatively and the result of replication is always the same information on half-new DNA molecules (1/2 parent strand, 1/2 daughter strand).
The polymerases also check for errors in the DNA and sort of proofread the nitrogen bases that they’ve already added. If the newly synthesized base does not match with the template’s original base, then the polymerase backtracks and replaces the incorrect base with the correct base. This reduces mistakes in replication (reduces mutations) at a rate of 1 mistake per 1 billion nucleotides.
Enzymes play a large role in breaking the hydrogen bonds to copy the DNA’s information and one the correct bases have been synthesized, create new hydrogen bonds to put the DNA molecules back together. As enzymes—in general—speed up multiple different processes in organisms, they also speed up the process of DNA replication, making eukaryotic replication an 8 hour process (for humans) when it could have taken almost a month to copy one DNA molecule.