8-mutation and repair

Question 1

what mutagens can cause mutations in dna?

Answer 1

viruses,uv,chemicals

Question 2

what are two sources of mutations for RNA? (general)

Answer 2

tautomery in transcription and damage to mRNA e.g truncation

Question 3

what are three sources of damage to proteins? (general)

Answer 3

1)mispairing a) of amino acid to tRNA by aminoacyl tRNA synthetase b) of codon to anticodon by ribosome and 2)protein misfolding

Question 4

what causes oxidative deamination?

Answer 4

free radicals

Question 5

what does depurination cause?

Answer 5

spontaneous hydrolysis and the production of a hole from A

Question 6

what causes thymine dimerisation?

Answer 6

UV light

Question 7

in thymin dimerisation what does thymine get converted to?

Answer 7

a cyclobutane dimer

Question 8

what can bromo-uracil be used for in experiments?

Answer 8

inducing mutations

Question 9

what does keto-bromo uracil pair to?

Answer 9

A

Question 10

what does enol-bromo uracil pair to?

Answer 10

C

Question 11

what ratio of keno-enol tautomery do bases usually have?

Answer 11

bias to keto form

Question 12

what keto-enol ratio does bromo-uracil have and why is it unusual?

Answer 12

has an even-ish mixture which is unusual as bases usually have bias to keto form

Question 13

describe difference between a missense and nonsense mutation?

Answer 13

nonsense–> STOP missense–> wrong aa

Question 14

what do missense,silence and nonsense mutation all have in common?

Answer 14

they are all point mutations

Question 15

what do indel mutations often cause? and what happens to the mRNA

Answer 15

frameshift which can lead to mRNA truncation

Question 16

why does frameshift lead to truncation?

Answer 16

because probability-wise 3/64 triplets will be STOP codons

Question 17

what can repair small DNA lesions? (4)

Answer 17

glycosylase,endonucleas,polymerase,ligase

Question 18

what does glycosylase do? how does it hep repair mutations?

Answer 18

can recognize odd base pairs and works by flipping out (uracil) by breaking glycosidic bonds

Question 19

what do nucleotide excisions fix?

Answer 19

Large DNA lesions

Question 20

what type of genes are given most attention by repair enzymes?

Answer 20

most actively transcribed genes

Question 21

what is repair often coupled with?

Answer 21

transcription

Question 22

true or false: the daughter strand is less often tragetted by repair enzymes than the template strand.

Answer 22

False, the daughter strand is more often targetted as it is more likely to contain error

Question 23

what two points have to maintain fidelity in translation?

Answer 23

1)ribosome decoding anticodon-codon 2)tRNA aminoacylation of tRNA-aminoacid

Question 24

what does streptomycin do to pyrimidines?

Answer 24

causes pyrimidines to be misread during translation

Question 25

what antibiotic inhibits ileRS (isoleucine tRNA synthetase) in MRSA?

Answer 25

newish antibiotic Mupirocin

Question 26

why do tRNAs have higher fidelity that amino acids?

Answer 26

tRNAs are larger and easily distinguishable by aminoacyl tRNA synthetase (aaRS). These synthetases join specific aa to cognate tRNA

Question 27

why do amino acids have a high error rate of 10^-2 aa?

Answer 27

they are small and easily confused e.g isoleucine and valine

Question 28

What is the aa error and the error after it has been reduced by aminoacyl tRNA synthetase proofreading activity?

Answer 28

10^-2 before which is reduced to 10^-4

Question 29

how does amino acyl tRNA synthetase reduce amino acid error?

Answer 29

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

Question 30

what is the tRNA error rate?

Answer 30

10^-4

Question 31

what is DNA error rate? a)with exonuclease activity of DNAP and b)with further processes

Answer 31

a)10^-6 b)10^-9

Question 32

what does melanin prevent?

Answer 32

thymine dimerisation that leads to cyclobutane dimer

Question 33

explain simply the difference between the genetic code being robust and redundant?

Answer 33

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

Question 34

what is an exception to the genetic code being robust?

Answer 34

the serine in the catalytic triad is very important

Question 35

why didnt an RNA world persist?

Answer 35

DNA may have had a selective advantage due to it being more stable and robust (RNA is more error prone)