Question

If DNA primase incorporated a mismatched nucleotide, how would that affect the organism? Justify your answer.

Answer 1

Answer:

DNA Primase Provides a starting point of RNA (or DNA) for DNA polymerase to begin synthesis of the new DNA strand. DNA polymerases are highly accurate, with an intrinsic error rate of less than one mistake for every 10⁷ nucleotides added.In addition, some DNA polymerases also have proofreading ability; they can remove nucleotides from the end of a growing strand in order to correct mismatched bases. Finally, post-replication mismatch repair mechanisms monitor the DNA for errors, being capable of distinguishing mismatches in the newly synthesized DNA strand from the original strand sequence. Together, these three discrimination steps enable replication fidelity of less than one mistake for every 10⁹ nucleotides added.

Misincorporation of nucleotides by DNA primase was examined using synthetic DNA templates of defined sequence. Primase seldom misincorporated NTPs during initiation of a new primer (i.e. polymerization of two NTPs to generate the dinucleotide). Following dinucleotide formation, however, primase readily misincorporated NTPs. Although the rate of misincorporation varied according to both the identity of the mismatch and the template sequence, primase is by far the least accurate nucleotide-polymerizing enzyme known. In some cases primase discriminated against incorrect NTPs by less than a factor of 100. After primase incorporated a noncognate nucleotide into the primer, the next correct NTP was readily added. Remarkably, primase could also polymerize consecutive noncognate nucleotides and generate primers containing multiple mismatches. Generation of a correctly base-paired primer-template negatively regulated further primer synthesis; however, generation of a primer-template containing multiple mismatches did not. After primase synthesized a primer containing multiple mismatches, the primer was transferred to the polymerase alpha active site via an intramolecular mechanism. Importantly, polymerase alpha readily elongated this primer if dNTPs were present.

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