8-mutation and repair Flashcards
what mutagens can cause mutations in dna?
viruses,uv,chemicals
what are two sources of mutations for RNA? (general)
tautomery in transcription and damage to mRNA e.g truncation
what are three sources of damage to proteins? (general)
1)mispairing a) of amino acid to tRNA by aminoacyl tRNA synthetase b) of codon to anticodon by ribosome and 2)protein misfolding
what causes oxidative deamination?
free radicals
what does depurination cause?
spontaneous hydrolysis and the production of a hole from A
what causes thymine dimerisation?
UV light
in thymin dimerisation what does thymine get converted to?
a cyclobutane dimer
what can bromo-uracil be used for in experiments?
inducing mutations
what does keto-bromo uracil pair to?
A
what does enol-bromo uracil pair to?
C
what ratio of keno-enol tautomery do bases usually have?
bias to keto form
what keto-enol ratio does bromo-uracil have and why is it unusual?
has an even-ish mixture which is unusual as bases usually have bias to keto form
describe difference between a missense and nonsense mutation?
nonsense–> STOP missense–> wrong aa
what do missense,silence and nonsense mutation all have in common?
they are all point mutations
what do indel mutations often cause? and what happens to the mRNA
frameshift which can lead to mRNA truncation
why does frameshift lead to truncation?
because probability-wise 3/64 triplets will be STOP codons
what can repair small DNA lesions? (4)
glycosylase,endonucleas,polymerase,ligase
what does glycosylase do? how does it hep repair mutations?
can recognize odd base pairs and works by flipping out (uracil) by breaking glycosidic bonds
what do nucleotide excisions fix?
Large DNA lesions
what type of genes are given most attention by repair enzymes?
most actively transcribed genes
what is repair often coupled with?
transcription
true or false: the daughter strand is less often tragetted by repair enzymes than the template strand.
False, the daughter strand is more often targetted as it is more likely to contain error
what two points have to maintain fidelity in translation?
1)ribosome decoding anticodon-codon 2)tRNA aminoacylation of tRNA-aminoacid
what does streptomycin do to pyrimidines?
causes pyrimidines to be misread during translation
what antibiotic inhibits ileRS (isoleucine tRNA synthetase) in MRSA?
newish antibiotic Mupirocin
why do tRNAs have higher fidelity that amino acids?
tRNAs are larger and easily distinguishable by aminoacyl tRNA synthetase (aaRS). These synthetases join specific aa to cognate tRNA
why do amino acids have a high error rate of 10^-2 aa?
they are small and easily confused e.g isoleucine and valine
What is the aa error and the error after it has been reduced by aminoacyl tRNA synthetase proofreading activity?
10^-2 before which is reduced to 10^-4
how does amino acyl tRNA synthetase reduce amino acid error?
example: with isoleucine and valine the usual active site is able to accomodate both amino acids however the esterase active site is smaller and can only accomodate valine
what is the tRNA error rate?
10^-4
what is DNA error rate? a)with exonuclease activity of DNAP and b)with further processes
a)10^-6 b)10^-9
what does melanin prevent?
thymine dimerisation that leads to cyclobutane dimer
explain simply the difference between the genetic code being robust and redundant?
robust- first amino acid different does not really affect function (retains polarity or not)
redundant- the fact 3rd letter does not matter and more than one codon codes for same aa
what is an exception to the genetic code being robust?
the serine in the catalytic triad is very important
why didnt an RNA world persist?
DNA may have had a selective advantage due to it being more stable and robust (RNA is more error prone)
