If DNA polymerase requires a perfectly paired primer in...

Name: Problem 7, Chapter 5: Molecular Biology of the Cell
Uploaded: 2024-01-22T07:09:48-08:00
Duration: 1 min 49 s
Channel: Anand Jangid
Description: If DNA polymerase requires a perfectly paired primer in order to add the next nucleotide, how is it that any mismatched nucleotides "escape" the polymerase and become substrates for mismatch repair enzymes?

If DNA polymerase requires a perfectly paired primer in order to add the next nucleotide, how is it that any mismatched nucleotides "escape" the polymerase and become substrates for mismatch repair enzymes?

Key Concepts

Kinetic Trade-Off in Replication

The kinetic aspects of DNA replication involve a balance between speed and accuracy; while DNA polymerase typically requires a perfectly paired primer end, the rapid incorporation of nucleotides means that a small number of mismatched bases can occasionally be accepted. This trade-off enables the replication machinery to sustain a high throughput while relying on subsequent correction systems, like mismatch repair, to further reduce the overall error rate.

Mismatch Repair System

The mismatch repair system is a post-replication surveillance mechanism that recognizes and rectifies base pairing errors that have escaped the polymerase proofreading function. It distinguishes the newly synthesized strand from the template and targets mispaired nucleotides or small insertion/deletion loops to maintain genetic stability.

Proofreading Mechanism

Many DNA polymerases have an intrinsic 3’ to 5’ exonuclease activity which serves as a proofreading mechanism to remove incorrectly incorporated nucleotides. This process significantly enhances replication fidelity by providing a chance to excise and replace mismatches immediately after they form, yet it is not 100% effective, allowing some errors to persist.

DNA Polymerase Fidelity

DNA polymerase is a critical enzyme in replication that ensures high accuracy by preferentially incorporating nucleotides that are correctly paired with the template strand. However, the enzyme’s selectivity is not absolute; due to rapid catalytic rates and the dynamics of molecular interactions, low-frequency errors can occur despite the high intrinsic fidelity of the polymerase.

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