EMS
ethyl methane sulphonate
makes a pre-mutagenic lesion by putting an ethyl group on guanine
makes GC—-> GT—–> AT
2-amino purine
base analogue
base pairs with thymine can also pair with cystine
AT—>AC—>GC
mutagen example in the aims test
aflatoxin - increases teh frequency of mutations in TA 100 Strain (GC—> AT)
chemically reacts with Guanine bases
what does aflatoxin B generate
apurinic sites (depurination) creates a ‘blank’ in DNA replication and a base is often inserted opposite this blank. DNA pol cant synthesise past these blanks and translesion DNA synthesis occurs which often incorporates the wrong DNA basei
which chemical mutagens alter bases in DNA and affect base-pairing
EMS
which mutagens ‘mimic’ normal bases which later causes the wrong base to pair
2-AP
which mutagens cause in an absence of ‘pairable’ bases
aflatoxin
how to repair EMS
alkyltransferases - transfers ethyl group from base to a protein
how to repair apurinic sites
enzyme = AP endonuclease; recognises apurinic site and cuts DNA strand
defective and adjacent DNA are removed with excision exonucleases
gap filled with DNA synthesis (excision repair)
how does radiation cause mutation
adjacent thymine can covalent cross link = photodimers
- fail to base-pair properly during DNA replication
translesion DNA pol can replicate but usually incorporate wrong bases
how to repair photodimers
nucleotide excision repair - similar to apurinic site repair
photolyase enzyme
- uses energy from white light to convert photodimers back to pyrimidines (photorepair)
