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MCD NAGE > protein translation and post-translational modification > Flashcards

protein translation and post-translational modification Flashcards

mechanism of translocation: summarise the mechanisms which ribosomes use to translate a mRNA sequence into a protein sequence, ensuring the fidelity of the genetic code

1
Q

structure of mRNA

A

diagram from NAGE 7

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2
Q

mRNA 5’ cap

A

entry site for ribosome

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3
Q

mRNA UTR

A

untranslated (regulation and stability)

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4
Q

mRNA poly A tail

A

protects from degradation

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5
Q

tRNA number of combinations

A

4 bases, codon requires 3 bases, so 4^3=64 amino acid combinations

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6
Q

how is fidelity of genetic code ensures

A

degenerate; more than 1 tRNA for each amino acid

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7
Q

tRNA diagram

A

diagram from NAGE 7

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8
Q

aminoacyl tRNA synthetase: function

A

bind tRNA to amino acid

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9
Q

aminoacyl tRNA synthetase: diagram

A

diagram from NAGE 7

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10
Q

peptidyl transferase: function

A

form peptide bonds between amino acids

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11
Q

chloramphenicol: function

A

inhibits peptidyl transferase

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12
Q

polyribosome definition

A

ribosomes working in multiple copies on mRNA

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13
Q

mRNA → protein sequence: initiation process

A

subunits dissociate (60S and 40S); complex forms with Met-tRNA (binds to P site; only Met can binds to 40S as first amino acid); eIFs (initiation factor) recognises and binds to mRNA; GTP → GDP + Pi for correct base pairing on eIF-2 after contact with first AUG (Met); 60S binds following conformational change caused by GTP hydrolysis

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14
Q

initiation inhibition

A

inhibited by streptomycin

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15
Q

mRNA → protein sequence: elongation process

A

new tRNA binds (with amino acid) to A (amino acyl) site; peptide bond formation by peptidyl transferase on 60S; tRNA translocates to P and first tRNA dissociates; ribosome shifts down one codon with aid of elongation factors using GTP; GTP hydrolysis allows pause so if incorrect base pair it will dissociate; elongation repeats

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16
Q

elongation inhibition

A

inhibited by puromycin

17
Q

mRNA → protein sequence: termination

A

recognition of STOP codon; release factors (proteins) bind to empty A; release of peptide chain (+H2O) catalysed by peptidyl transferase; ribosome and release factors dissociate

18
Q

termination inhibition

A

inhibited by chloramphenicol

19
Q

ribosome recognition: start and end sequences

A

start at AUG (Met); end at first inframe termination codon: UAG, UAA, UGA

MCD NAGE (17 decks)

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