Mismatch Repair Animation

Summary

This transcript discusses the role of DNA polymerase in DNA replication and its proofreading function, which helps prevent misincorporation of bases. It highlights that despite this precision, errors can still occur, leading to mismatches that distort the DNA structure. The mutation rate in E. coli is low due to effective repair mechanisms, particularly methyl mismatch repair. This process involves recognizing methylation patterns to distinguish between the parental and newly synthesized strands. Key proteins in this repair system work together to correct mismatches, illustrating the intricate processes that maintain genetic fidelity.

Takeaways

• 😀 DNA polymerase has a proofreading function that reduces mis-incorporation of bases during DNA replication.
• 😀 Approximately one incorrect base is incorporated for every million bases synthesized by DNA polymerase.
• 😀 Despite the high accuracy, mutations occur at a rate of one in every billion bases in E. coli.
• 😀 E. coli employs various repair mechanisms to address mismatches that arise during DNA replication.
• 😀 Methyl mismatch repair is a key method for correcting errors by recognizing methylation patterns in DNA.
• 😀 The palindromic sequence GATC in E. coli is specifically targeted for methylation.
• 😀 Methylation allows the cell to differentiate between the parental strand and the newly synthesized strand.
• 😀 A series of proteins, including MutS, MutL, and MutH, play critical roles in the mismatch repair process.
• 😀 The mismatch repair process involves cleaving the unmethylated strand, which contains the mutation.
• 😀 DNA polymerase fills in the gap with the correct nucleotide, and DNA ligase seals the remaining break.

Q & A

What is the primary function of DNA polymerase?

The primary function of DNA polymerase is to replicate DNA and incorporate nucleotides to synthesize new DNA strands.

What is the proofreading function of DNA polymerase?

The proofreading function of DNA polymerase prevents the mis-incorporation of bases during DNA synthesis.

How often does DNA polymerase incorporate an incorrect base?

DNA polymerase incorporates an incorrect base approximately once in every one million bases synthesized.

What is the mutation rate in E. coli cells?

The mutation rate in an E. coli cell is about one for every one billion bases replicated.

What is methyl mismatch repair?

Methyl mismatch repair is a method used by cells to recognize and correct mismatched bases in DNA based on methylation patterns.

How does methyl mismatch repair distinguish between the parental and new strands?

It distinguishes strands by the methylation pattern; the parental strand is methylated while the new strand is not immediately methylated.

What role do the proteins called MutS and MutL play in mismatch repair?

MutS binds to the mismatch and recruits MutL, which recognizes the methylated strand and facilitates the repair process.

What happens to the unmethylated strand during the mismatch repair process?

The unmethylated strand containing the mutation is cleaved and unwound, exposing it for repair by exonucleases.

How is the gap left by the removal of the mismatch filled?

The gap is filled in by DNA polymerase I, which inserts the correct nucleotide, and then the remaining gap is sealed by DNA ligase.

What are the consequences of defects in methyl mismatch repair proteins?

Defective strains in methyl mismatch repair proteins have a high mutation rate, leading to increased genetic instability.