BCH4024 Douma Exam 4 - Lecture 13

What is a mutation?

An accidental, permanent change in a DNA sequence.

What does a nonsense mutation do?

Introduces a premature stop codon.

What does a missense mutation do?

Replaces one amino acid codon with another.

What is a silent mutation?

A mutation that changes the DNA sequence without altering the encoded protein.

What is a frameshift mutation?

An insertion or deletion that is not a multiple of 3 bases, often leading to an early stop codon.

What is an inframe mutation?

Addition/deletion of nucleotides that does not affect the reading frame (has to occur in sets of 3s).

What is DNA damage?

An abnormal chemical structure of DNA that can be spontaneous or environmentally caused.

What are the most common types of DNA damage?

Single-strand breaks and depurination.

What causes deamination in DNA?

Spontaneous reactions and exposure to sodium nitrate/nitrite, tobacco, pesticides, and gastric juices.

What causes oxidation of DNA?

Reactive oxygen species generated by cellular respiration.

What is depurination?

Hydrolysis of the glycosidic bond linking a purine base to the sugar-phosphate backbone, creating an abasic site.

What is alkylation of DNA?

Covalent modification of bases in DNA, such as by sulfur mustard or spontaneous alkylation by S-adenosylmethionine.

What causes thymine dimers?

Ultraviolet radiation forming a cyclobutane ring between adjacent thymines.

What causes DNA strand breaks?

Ionizing radiation like cosmic rays, X-rays, and radioactive materials.

What are the four general steps of DNA repair?

Recognition, excision, resynthesis, and ligation.

What does mismatch repair (MMR) correct?

Mismatched base pairs mainly from errors in replication.

What proteins are involved in mismatch repair in E. coli?

MutL-MutS complex recognizes the mismatch, MutH nicks the unmethylated strand.

What initiates base excision repair (BER)?

DNA glycosylase removes the damaged base creating an abasic site.

What repairs abasic sites in BER?

AP endonuclease creates a nick and DNA Pol I (or DNA Pol β in eukaryotes) fills the gap.

What type of damage does nucleotide excision repair (NER) fix?

Lesions that distort the DNA double helix, like thymine dimers or alkylation.

What enzymes are involved in NER?

UvrABC excinuclease (prokaryotes) or XP excinuclease with TFIIH (eukaryotes).

What is non-homologous end joining (NHEJ)?

An error-prone repair mechanism for double-strand breaks predominant in G0 and G1.

What proteins are involved in NHEJ?

Ku70/80, PKcs, exonucleases, DNA pol μ/λ, Artemis endonuclease, DNA ligase.

What is homologous recombination repair (HRR)?

An error-free repair mechanism for double-strand breaks using the sister chromatid as a template during S and G2 phases.