Gene Mutations and DNA Repair

Flashcards covering gene mutations, DNA damage, and DNA repair mechanisms, including nucleotide excision repair, base excision repair, mismatch repair, and double-strand breakage repair.

What is a gene mutation?

Change in the genetic information at a specific location on the DNA.

What are the types of base pair changes in gene mutations?

Deletion, insertion, transition, and transversion.

What is a transition mutation?

A purine base replaces a purine base, OR a pyrimidine base replaces a pyrimidine base.

What is a transversion mutation?

A purine base replaces a pyrimidine base, OR vice versa.

What is the effect of deleting a base pair?

All codons after this point are altered, leading to a frameshift mutation.

What type of mutation is caused when a pyrimidine base is swapped for the other pyrimidine base, such as C changed to T?

Transition mutation.

What type of mutation is caused when a pyrimidine base is swapped for a purine base, such as C changed to A?

Transversion mutation.

What is a single nucleotide polymorphism (SNP)?

A single nucleotide change in DNA.

Give an example of a disease caused by a SNP.

Sickle cell anaemia.

What is the effect of a SNP that causes a premature stop codon?

Short, non-functional protein.

Name three types of damage that radiation can cause to DNA.

Ionising radiation causes double-stranded breaks, UV radiation causes pyrimidine dimers.

How does heat damage DNA?

Causes depurination, where adenine and guanine bases are split from the sugar-phosphate backbone.

What are the three principal forms of chemical damage to DNA?

Direct binding to DNA, de-amination, direct reaction with base.

Name three examples of direct reaction with a base causing chemical damage to the DNA.

Methylation, hydrolysis, oxidation of base.

What are DNA lesions?

Alterations in the DNA caused by damage.

What is the role of DNA repair systems?

To avoid mutations in cells.

List four DNA repair mechanisms

Nucleotide excision repair, base excision repair, mismatch repair, and double-strand breakage repair.

What is nucleotide excision repair (NER)?

A ‘cut & patch’ mechanism active against bulky lesions, such as pyrimidine dimers from UV damage.

Name two distinct NER pathways.

Transcription-coupled pathway and global pathway.

What is the role of DNA glycosylases in base excision repair?

To remove the altered base from the sugar.

What is the role of AP endonuclease (APE) in base excision repair?

To cleave the sugar-phosphate backbone, creating a nick.

How does DNA polymerase β contribute to base excision repair?

Removes the sugar-phosphate remnant and inserts the correct deoxyribonucleoside triphosphate (dNTP).

What is the function of the two active sites of DNA polymerase?

1) catalyse nucleotide polymerisation and 2) proofread the new DNA strand and edit out mismatched base pairs.

How does MutS protein contribute to mismatch repair?

Recognizes the mismatch.

How does MutL protein contribute to mismatch repair?

Scans for the nick on the new strand in mismatch repair.

What causes double strand breaks in DNA?

Ionising radiation, stalled replication, reactive oxygen species.

What is the most common repair pathway for double strand breaks in mammalian cells?

Non-homologous end joining (NHEJ).

What are the possible outcomes of a mutation in DNA?

Non-functional proteins, senescence, apoptosis, or cancer.