Mutations Flashcards
Give an example of an error that can occur during DNA polymerisation
Incorporation of the wrong base isomer
How does UV radiation affect the DNA
Promotes formation of intrastand thymine dimer = covalent bonds between consecutive bases = DNA disrupted and transcription/translation is altered
How does UV radiation affect the DNA
Promotes formation of intrastand thymine dimer = DNA disrupted and transcription/translation is altered
Name and explain the two types of point mutations
Transitions ( conversion from one purine to another purine or one pyramidine to another pyrimidine e.g. A to G or C to T )
Transversions ( conversion of a purine to a pyrimidine or vice versa e.g A ⇒C/T)
Effect of alkylating agents
Generate transversions
What is a polar mutation
Mutation that affects genes/operons downstream
Name the types of chromosomal mutation
Recombination Deletions
duplication
What do alkyl transferases do
They reverse base methylation caused by some alkylating agents by removing methyl/ethyl groups and adding them to their own residues
Base excision repairs
Not all damaged bases can be repaired - some must be removed and replaced
Glycosylases cleave the glycosidic bond of the corresponding altered nucleotide
this leaves a deoxyribose residue without a base (called apurinic or apyrimidinic )
Deoxyribose residue is cleaved on the 5’ side by AP endonuclease
DNA polymerase adds in new base and DNA ligase reseals the DNA
Describe nucleotide excision repair
Corrects pyrimidine dimers and other displacement of bases
acts as a major defence against carcinogens in tobacco and sunlight
what are the ways double strand DNA breaks can be fixed
Non-homologous end joining (NHEJ)
Recombination repair
Mismatch repairs
fixes mismatches during DNA replication
Carried out by MUT proteins
defects result in cancer
Describe NHEJ
Protein Ku acts as a broken DNA sensor
Ends of broken DNA must be aligned (carried out by action of Ku )
frayed ends trimmed or filled in and strands must be lighted
