long question (8) Flashcards
1
Q
what mechanism do cells use for DNA repair and give an example of a mutation and a repair mechanism
A
2
Q
mechanisms cell use for DNA repair
A
- deoxydipyrimidine photolyses
- DNA methyl transferase
- glycosylase
3
Q
what is deoxydipyrimidine photolyses
A
- light-dependent, only works in UV-exposed skin
- photolyase (enzyme) cleaves thymine dimers
- DNA is not cut therefore error free
- damage not repaired leads to skin cancer
4
Q
what is DNA methyl transferase
A
- enzyme
- reverse alkylating agents
- transfers methyl/ethyl groups from guanine and thymine to an internal cysteine residue
- error free
5
Q
what is glycosylase
A
- removes alkyated or foreign bases
- cleaves nucleoside bonds between deoxyribose sugar and base
- leaves apurinic/apyrimidinic i.e. no base
- base excision repair
- helix distortion
- error (mutation) = adds incorrect base
6
Q
example of a mutation
A
multisite mutations
7
Q
what are multisite mutations
A
- contain more than one base change
- deletions + insertions
8
Q
what are deletions
A
- most common
- don’t back mutate
- extensive changes will have severe effect
- small changes can have small e.g. 3 bases can delete one amino acid
- small changes can have small and big effects e.g. 4 bases can delete one amino acid & change reading frame
9
Q
what are insertions
A
- usually in the form of a recombination event
- can move around genome “jumping genes”
- possibly from viruses
- genetic elements
- disrupt transcription/translation
- important in evolution
10
Q
phenylketonuria
A
- autosomal recessive inheritance i.e. 2 mutant copies are needed
- mutations in the phenylalanine hydroxylase gene on chromosome 12q
- variation in PKU is due to heterogeneity in the mutant alleles