Describe two ways by which DNA polymerase ensures that the correct base is added
ID: 54869 • Letter: D
Question
Describe two ways by which DNA polymerase ensures that the correct base is added to the growing polynucleotide chain during replication, addressing what these mechanisms have in common, and how they differ. What is the contribution of these mechanisms toward the overall fidelity of DNA replication? Describe two ways by which DNA polymerase ensures that the correct base is added to the growing polynucleotide chain during replication, addressing what these mechanisms have in common, and how they differ. What is the contribution of these mechanisms toward the overall fidelity of DNA replication? Describe two ways by which DNA polymerase ensures that the correct base is added to the growing polynucleotide chain during replication, addressing what these mechanisms have in common, and how they differ. What is the contribution of these mechanisms toward the overall fidelity of DNA replication?Explanation / Answer
The two ways are described as follows:
1. Kinetic proofreading- The exclusive ability of correctly paired bases to fit properly within the enzyme's active site determines the reliability of this method. In case the incoming nucleotide is not complementary to template base present at the active site, then proper alignment of the nucleotide cannot take place with the template. This slows down the polymerization reaction. This in turn gives time to the incorrectly matched nucleotide so that it can leave the active site and then be replaced by a correctly matched nucleotide. Polymerase's error rate is reduced to about 10-5 due to kinetic proofreading.
2. 3' - 5' exonuclease activity- This method makes use the of many DNA polymerases. The exonuclease activity allows the polymerase to backtrack and remove the recently incorporated nucleotide into the primer strand. This activity works on correctly as well as incorrectly-matched nucleotides.However, it is much more active in removing incorrectly matched nucleotides because incorrectly paired bases tend to slow the polymerase down and this gives the exonuclease more time remove the nucleotide. Polymerase's error rate is reduced to about 10-7 due to 3'-5' exonuclease activity.
When it comes to maintain the stability of genomes which contain large amounts of repetitive DNA, DNA polymerases play a major role. It is only due to the ability of polymerases to ensure correct base addition in the polynucleotide chain that the error rate in the chain is reduced. Less error means more stable genome. In this way these mechanisms contribute to the overall fidelity of DNA replication.