BIO MODULE 4:Set 6 — DNA Repair, Proofreading & Mutations

What are the three basic steps of DNA repair?

Recognize and remove the error, replace the removed DNA, and seal the repaired strand.

What are the three main DNA repair mechanisms discussed in the lecture?

Proofreading, mismatch repair, and excision repair.

What is proofreading during DNA replication?

DNA polymerase checks newly added nucleotides and removes incorrect ones.

What is the most common error during DNA replication?

Base-pair mismatches.

Which enzyme performs proofreading during DNA replication?

DNA polymerase.

What is 3′ to 5′ exonuclease activity?

The ability of DNA polymerase to remove an incorrectly added nucleotide from the 3′ end of a growing strand.

What happens after DNA polymerase removes an incorrect nucleotide?

It resumes DNA synthesis and inserts the correct nucleotide.

What is mismatch repair?

A repair mechanism that corrects replication errors that escape proofreading.

How are mismatched bases recognized during mismatch repair?

They cause distortions in DNA structure that repair enzymes can detect.

What happens during mismatch repair?

The incorrect section of the new DNA strand is removed, replaced by DNA polymerase, and sealed by DNA ligase.

Which enzyme fills the gap during mismatch repair?

DNA polymerase.

Which enzyme seals the repaired DNA strand?

DNA ligase.

What is excision repair?

A repair mechanism that removes and replaces damaged DNA.

What can cause DNA damage that requires excision repair?

Chemicals and radiation.

What are the two types of excision repair discussed in the lecture?

Base-excision repair and nucleotide-excision repair.

What type of damage is repaired by base-excision repair?

Nonbulky damage to individual DNA bases.

What type of damage is repaired by nucleotide-excision repair?

Bulky DNA damage that causes more extensive distortion of the DNA helix.

What is a mutation?

A change in the DNA sequence that can be passed on in replicated DNA copies.

What is a primary source of mutations?

Errors that remain in DNA after proofreading and repair.

How can a mutation affect a gene?

It may alter the protein encoded by that gene.

How can mutations affect an organism?

They can change protein function and potentially alter how the organism functions.

Why are mutations important for evolution?

They create genetic variation that natural selection can act upon.

What is the relationship between DNA repair and mutation frequency?

DNA repair reduces the number of errors that persist as mutations.