Is the repair of damaged DNA best viewed as a race between an endonuclease and DNA ligase Helicase Methylase DNA polymerase or Primase?

Answer 1

It's not really a race at all as the processes cooperate with each other, but there are two possible analogies from your options.

The first, and the most applicable to living cells, is a race between polymerase and methylase. However, this is only the case in prokaryotes (bacteria etc) and not in eukaryotes (humans, animals, plants etc) because the latter don't methylate their DNA. The reason for this "race" is that the prokaryotic repair enzymes use hemi methylated sites (only methylated on one side) to identify which of the two bases in a mismatched base pair is incorrect (it will be the newest unmethylated one). If the methylase gets there before the repair enzymes do, then there will be no way to tell and repair is limited to homologous recombination, which can't always take place as it relies on a homologous chromosome (an exact copy) being present. But in a living cell, methylase always lags behind polymerase and the repair enzymes to avoid this happening.

The second possible "race" is between the endonuclease and the polymerase, since polymerase replicates DNA and endonuclease (in this case) repairs it. If the polymerase replicates DNA before damage repair, you get cell division with a permanent mutation in one cell, which is why they could be considered to "race". But realistically, if polymerase comes across any DNA damage, it will usually stop and wait for the repair to take place anyway, and actively recruits the necessary enzymes to do so.