DNA Repair Lecture Notes

A set of flashcards summarizing key concepts from the DNA Repair lecture, designed to assist in exam preparation.

What is mutagenesis?

The creation of mutations.

What can cause DNA damage during replication?

Heat, chemicals, and irradiation.

How does heat affect DNA?

Can speed up chemical reactions, leading to deamination of bases.

What are mutagens?

Treatments that generate mutations.

What happens to cells with no DNA repair mechanisms after mutagenic treatment?

Each mutation could cause a lethal hit to DNA.

What is the effect of DNA repair mechanisms on cell survival during mutagenic treatment?

Cells can cope with low levels of mutagenesis.

What can lead to overwhelming the DNA repair systems?

Longer or stronger treatment leading to too many mutations.

Name specific types of damage DNA repair pathways address.

Damage due to deamination, reactive oxygen, alkylating agents, and UV radiation.

What is a common type of damage that occurs spontaneously or via deaminating agents?

Deamination of bases.

What do hydroxylamine and nitrous acid do to DNA?

Deaminate cytosine to uracil and deaminate adenine and guanine, respectively.

What role do DNA N-glycosylases play in DNA repair?

They break the glycosyl bond between the base and the sugar.

What do AP endonucleases do in the DNA repair process?

Cut the sugar-phosphate backbone next to an apurinic or apyrimidinic site.

What are superoxide radicals and hydrogen peroxide examples of?

Reactive forms of molecular oxygen that can cause DNA damage.

What is 8-oxoG known for?

It is one of the most mutagenic lesions due to reactive oxygen.

What does DNA pol III tend to mispair 8-oxoG with?

Adenine (GC to TA transversion).

Name one mechanism E. coli uses to avoid 8-oxoG mutations.

Mut M, which removes 8-oxoG from DNA.

What happens when alkylating agents interact with DNA?

They add alkyl groups to the bases, causing mispairing.

What are examples of alkylating agents?

Ethyl methanesulfonate (EMS), methyl methanesulfonate (MMS), and nitrosoguanidine (NTG).

What type of damage is linked to UV radiation?

Fusions between adjacent pyrimidines forming pyrimidine dimers.

Describe photoreactivation. What is the role of photolyase?

It separates fused bases of dimers in the presence of visible light.

What type of DNA damage is repaired by the methyl-directed mismatch repair system?

Mismatches and minor distortions in the DNA helix.

What are base analogs?

Chemicals that resemble normal DNA bases.

How does 2-aminopurine (2-AP) behave during DNA synthesis?

It may pair incorrectly with cytosine or correctly with thymine.

What do frameshift mutagens do?

They intercalate between bases, preventing proper alignment with the opposite strand.

What are common examples of frameshift mutagens?

Acridine dyes, such as ethidium bromide.

What is the function of the mutS, mutL, and mutH genes in a DNA repair process?

They help recognize and repair DNA mismatches.

What type of GATC site do the MDMR (Methyl-Directed Mismatch Repair) mechanisms depend on?

A hemimethylated GATC site.

What phenotype might you expect from mut mutations?

A high mutation rate leading to a mutator phenotype.

What method is used to detect mutants with high mutation rates?

Colony papillation.

What allows lac+ revertants of lac mutations to signal hyper mutators?

The formation of blue papillae on X-gal plates.

What happens to DNA in nucleotide excision repair?

Damaged nucleotides are excised and replaced.

What types of DNA damage does nucleotide excision repair address?

Major distortions, such as those caused by UV irradiation.

What are the uvrA, uvrB, and uvrC genes responsible for?

Forming a complex that initiates nucleotide excision repair.

What triggers the induction of nucleotide excision repair genes?

DNA damage causes expression of these genes to increase significantly.

What is the role of Mfd protein in nucleotide excision repair?

Helps unjam RNA polymerase and guides repair mechanisms to damage sites.

What is the significance of LexA in the SOS response?

It represses transcription of SOS genes until extensive DNA damage occurs.

How does RecA aid in the SOS response?

It induces cleavage of LexA, allowing SOS gene transcription.

What is translesion synthesis?

A DNA replication process that allows replication over damaged DNA.

What enzyme does the umuCD operon code for?

DNA polymerase V, which is used during translesion synthesis.

What happens to DNA replication when UmuD2C is formed?

It can displace DNA pol III and continue replication over damaged sites.

What occurs after DNA pol III encounters damaged DNA?

It becomes stalled, allowing other mechanisms to take over.

What trade-off occurs during translesion synthesis?

Cells survive but may incorporate mutations as a result.