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CBG PANT Replication, transcription and translation > CBG Lecture 8: Mutation and Repair > Flashcards

CBG Lecture 8: Mutation and Repair Flashcards

1
Q

how are mutations in DNA introduced

A

spontaneous

introduced by mutagens: virus/UV/chemicals

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2
Q

name some mutagens

A

virus
uv
chemical

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3
Q

per how many bases does polymerisation make a mistake 1

A

10^4 or 10^5

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4
Q

of the bases that polymerisation makes a mistake on, how many does exonuclease proofreading fail to correct

A

1 in 100 of 10^4 mistakes

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5
Q

what is the overall error rate of polymerisation

A

10^-9 per nucleotide

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6
Q

give some examples of where mutations can arise

A 
tautomery during replication/transcription
mispairing of aa to tRNA by aaRS
mutations in DNA by mutagens
damage to mRNA eg. truncation
misfolding of proteins by prions
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7
Q

how is /dna prone to mutations

A

oxidative deamination by free radicals
depurination - spontaneous hydrolysis
thymine dimerisation by UV light

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8
Q

how does thymine dimerisation occur

what does it make

A

by UV light

cyclobutane dimer

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9
Q

what happens to cytosine in oxidative deamination

how does it happen

A

cytosine + free radicals -> uracil

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10
Q

what happpens to a depurinated adenine

A

adenine + spontaneous hydrolysis -> hole

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11
Q

how is hole made

A

by spontaneous hydrolysis and depurination of adenine

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12
Q

how is thymine dimerised

what does it make

A

thymine is dimerised by UV light and makes a cyclobutane dimer

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13
Q

what do uncorrected lesions lead to

A

mutation

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14
Q

name a potent mutagen

A

5-bromouracil

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15
Q

in what way can smaller lesions be repaired

A

base excision by a glycosylase, endonuclease, polymerase, ligase

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16
Q

in what way can large lesions be repaired

A

nucleotide excisions

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17
Q

name subtypes for a mutation with point change in a single base

A

missense
nonsense
silent

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18
Q

what is a missense mutation

A

change in codon (normally second base) leads to change in aa

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19
Q

give an example of a missense mutation disease

A

glu -> vale
(GAG->GUG)
sickle cell anaemia (Hb)

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20
Q

give an example of a nonsense mutation

A

GGA -> UGA
gly -> STOP
chloride channel : cystic fibrosis

21
Q

what is a nonsense mutation

A

change in codon, making it a STOP codon

22
Q

what is a silent mutation

A

change in base, no change in aa

23
Q

what is an indel mutation

A

insertion or deletion of base

24
Q

what is a frameshift mutation

A

when an INDEL occurs causing the reading of the bases to no longer be read the same

25
Q

what does a frameshift mutation often cause

A

protein truncation as 3/64 triplets will be STOP codons

26
Q

why is it that many lesions are easily repaired

A

because DNA is double stranded

27
Q

what does DNA glycosylase do? how?

A

flips out and breaks the glycosidic bond between DNA and uracil in a U:G lesion

28
Q

what process is repair often coupled with? why

A

repair is often coupled to transcription, ensuring that the most used genes (those actively transcribed) are given the most attention by repair enzymes

29
Q

why is it that daughter DNA strands are often distinguishable from the parente strand for a while after replication

A

because of the lag in post-replicative modification of the DNA eg. by methylation so the daughter strand (which is more likely to contain the error) will be more likely to be targeted for correction

30
Q

what do prokaryotes use to deal with mistranscribed, truncated mRNA

A

tmRNA - transfer messenger RNA

31
Q

what does tmRNA encode

A

has an mRNA like domain encoding the degradation tag ANDENYALAA

32
Q

name some functions of tmRNA

A

deals with mistranscribed truncated mRNA
recycles the stalled ribopsome
adds a proteolysis inducing tag to the unfinished pp
facilitates the degradation of aberrant mRNA

33
Q

at which two points in translation does fidelity need to be maintained

A
  1. ribosome decoding of codon to anticodon

2. tRNA aminoacylation of tRNA to amino acid

34
Q

what is the effect of streptomycin

A

causes pyrimidines to be misread during translation

35
Q

what is the effect of mupirocin

A

new antibiotic that inhibits IleRS in MRSA: inhibits aminoacyl synthetases

36
Q

describe tRNAs

A

large and easily distinguished by aaRS

readily distinguishable by their anticodons

37
Q

what are aaRS

A

alanyl-tRNA synthetase
helps attach the aa to the tRNA
have proofreading esterase

38
Q

what is the error rate of tRNA

A

10^-4 per tRNA

39
Q

what AS’s do aaRS’s have

A

aminoacylation active site - large enough to accommodate aa

esterase proofreading active site smaller

40
Q

in what way is genetic code robust

A

the mutations that do make a difference to the encoded mutations very rarely replace a hydrophobic amino acid with a very polar one or vv

41
Q

in what way is the genetic code redundant

A

several codons code for the same amino acid because the third base of the codon is usually irrelevant

42
Q

what is the difference in binding eneryies between valine and isoleucine

A

difference in one CH2

difference in binding energy is 12kJmol-1

43
Q

name 2 enzymes that have separate active sites for the process and and for proofreadin

A

DNAP

aaRS

44
Q

why is it good for an enzyme to have proofreading performed by a separate active site

A

ensures the two processes are independent and that the probability of error is minimised since it will make the probability the product of two independent processes

45
Q

name some confusing amino acid pairs

A

valine : isoleucine:leucine
alanine + glycine
aspartamine + glycine
serine and lysine

46
Q

what happens to errors that do slip through

A

degradation mechanisms to fix or remove them

47
Q

what do aaRSs do

A

catalyse the esterification of a specific amino acid to its compatible cognate tRNA

48
Q

in which number base of a codon does a mutation make little difference to codon

A

first base

CBG PANT Replication, transcription and translation (10 decks)

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