G1 Flashcards
what is a silent mutation
and a synonomous mutation
triplet encodes the same AA
syn = codon specifies different but functionally equivalent
what could mutation in intron cause
including in exon,
what could mutation in promoter cause
over/under expression
what are the 3 mechanisms that mutagens act through?
replacing a base
altering a base
damaging a base
what kind of mutagens induce base replacement
base analogue
chemical analogue of natural bases
incorperated into dna in place of normal base can cause errors in replication and high rate of tautomeric shift
what is tautomeric shift
base present in one of several forms (isomers)
taumeric shift is the sponatenous isomerisation of a nitrogen base to an alternative hydrogen bonding form
what is the normal tautomeric form in DNA bases
keto form
what happens if you get imino form of cytosine
pairs with adenine
what happens if ou get imino for of adenine
pairs with cytosine
what happens if you get the enol form of thymine
pairs with guanine
what happens if you get the enol for of guanine
pairs with thymine
what is 5- bromo uracil
in keto form is a thymine analogue contains bromine at C5 instead of CH3
what does 5-bromouracil do in dna
in keto form still pairs to adenine
however presence of bromine modifies electron distributtion of ring, can be enol form or ionised form
which pairs with guanine
= promotes transitions
what effect does nitrous acid (HNO2) have on the bases
promotes oxidative deamination converting NH2 amino groups to keto groups
cytosine ->uracil (pairs A)
Adenine -> hypoxanthine (pairs c)
Guanine -> Xanthine (pairs C)
what type of organism does nitrous acid work best in
prokaryotes
what do alkylating agents do
cause specific mispairing
what type of organism do alkylating agenets work best in
both pro and euk works well
what are two common alkylating agents
EMS and NMG
ethylmethanesulfonate and nitrosoguanidine
what is the most mutagenic wavelength of UV
254nm
what does UV light do to DNA
- what are the knock on effects of this
cause dimers between adjacent pyrimidines
TT or TC dimers distorting double helix and interfereing wiith replication
the wrong base can then be inserted opposite them causing a missense/nonsense mutations
= premutational lesion
What is human xeroderma pigmetosum
a autosomal recessive disease that is caused by a defect in excision repair of pyrimidine dimers
What is the SOS system in E.coli
last resort damage tolerance that allows cells to survive with a degree of mutagenesis
describe the SOS system in E.coli
UmuC or UmuD genes (which encode subunits of DNAPV)
code for error prone polymerases
DNAP3 stops at a non coding lesion (eg photodimer)
generating ss regions that attract Ssb protein and Rec A which form filaments
presence of RecA filaments signals cells to synthesize UmuD which is cleaved by RecA to yield UmuD adn UmuC
UmuC forms a complex with UmuD allowing DNAP to proceed past the lesion.
what eukaryotes have been found to code for error prone polymerases as in SOS
yeast
