Biochemistry PS - Translation

Question 1

What allows tRNAmet to bind?

Answer 1

Recruitment of eIF4F to the 5’ cap then eIF4A and eIF4B

Question 2

What do eIF4F, A and B function to do?

Answer 2

Create a binding site for tRNAmet-eIF2, and the 40S ribosomal subunit

Question 3

What happens after eIF4F recruitment?

Answer 3

3’direction scanning of mRNA until AUG is recognised.

Question 4

Why is the AUG codon signification?

Answer 4

It marks the methionine amino acid for synthesis.

Question 5

What happens when AUG is recognised?

Answer 5

eIF5 release alls initaition factors and 60S subunit is recruited.

Question 6

What are the three binding sites of the 60S subunit(right to left)?

Answer 6

Exit, Peptidyl and Aminoacyl

Question 7

What does the tRNA-met do in initation?

Answer 7

It is in the P site, whilst either side are empty

Question 8

How does tRNA associate to the mRNA?

Answer 8

tRNA anticodon arm hydrogen bonds for AUG codon bases.

Question 9

Monocistronic

Answer 9

This means only one gene is produced from a promoter region of a stretch of replication DNA

Question 10

What is eukaryotic mRNA in regards to their expression capabilities?

Answer 10

Monocistronic

Question 11

When is elongation marked as starting?

Answer 11

EF-1A-GTP recruited into initation complex.

Question 12

How is movement of the ribosomal subunits mediated?

Answer 12

EF-1a/EF2 hydrolysis of their associated GTP into GDP.

Question 13

What happens when EF-1a-GTP is first hydrolysed?

Answer 13

40S subunit moves one down, new charged tRNA recruited at A site of 60s, where new EF-1a-gtp is found.

Question 14

What is required for EF-1a-GTP hydrolysis?

Answer 14

codon-anticodon resemblence

Question 15

What happens when EF-1a-GTP hydrolysis occurs secondly?

Answer 15

CC clamps charged tRNA allowing peptidyl transferase to catalyse peptide bond formation.

Question 16

What is peptide bond formation coupled with?

Answer 16

Breakage of bond connecting amino acid to tRNA.

Question 17

What happens after the peptide bonds are formed?

Answer 17

60s moves along, tRNA in the P and A shift to E and P.

Question 18

How quick is tranlastion elongation?

Answer 18

15 amino acids per second.

Question 19

What happens when the termination codon is encounted?

Answer 19

Release factor binds ribosome, cleaving remaining tRNA from PP chain by GTP hydrolyis.s

Question 20

What are the stop codons?

Answer 20

UAA, UAG and UGA

Question 21

What are the two types of regulation mechanisms?

Answer 21

Prevention of incorporation of errors and termination of PP synthesis when an error is incorporated.

Question 22

What an example of prevention of error?

Answer 22

Regualtory proteins binding introns, removed just prior to translation assuming not bound to introns

Question 23

Why are introns potentially bad for mRNA?

Answer 23

Because they are long enough to usuually contain a stop codon spontaneously.

Question 24

What happens if an intron gets through?

Answer 24

Protein markers remain before being stripped away, inducing nuclease destruction of the mRNA

Question 25

Nonsense-mediated decay

Answer 25

This prevents translation of mutant mRNA harbouring premature termination codons by targeting them for degradation.

Question 26

What may assist protein folding?

Answer 26

Nascent Chain Associated Complex or chaperones like HSP40/70/90 or chaperonins?

Question 27

What do chaperones do?

Answer 27

Bind hydrophobic regions to prevent aggregation, allowing time for folding.

Question 28

What do chaperonins do?

Answer 28

Cylindrical structures providing safe-envrionment for folding to occur.

Question 29

What mediates translation of mRNA to amino acid sequence?

Answer 29

Charged tRNA molecules, ie aminoacyl-tRNA synthestase

Question 30

Structure of mRNA in 2D?

Answer 30

Four0clover leaf, containing an anticodon opposing the amino acid attachment site and a D loop opposing the T loop

Question 31

Importance of the anticodon loop?

Answer 31

Base pairs with mRNA sequence

Question 32

Amino acid attachment site...

Answer 32

A 3; 0H group terminated by a CCA end where amino acid is attached by aminoacyl tRNA synthetase

Question 33

What happens when synthetase binds tRNA attachment site?

Answer 33

Part of protein contacts T loop guiding the acceptor arom into enzymes active site

Question 34

D Arm

Answer 34

Recognition site for aminoacyl-tRNA synthetase

Question 35

T Arm

Answer 35

Recognition site for the ribosome to form a tRNA ribosome complex

Question 36

Function of eIF5?

Answer 36

Interacts with 40s iniation complex to promote GTP hydrolysis joining 60S subunit to 40S initaiton complex

Question 37

43S pre-initation complex

Answer 37

A ribonucleoprotein in early translation containg the EIFs

Question 38

First step of intiation

Answer 38

AUG start codon is in the P site of the ribosome with a met-tRNA naticodon base pair ON the mRNA

Question 39

Second step of initaiton

Answer 39

43S PIC contaiing met-tRNA and many EIF recruited to 5' cap of the mRNA

Question 40

Third step of initation

Answer 40

The PIC scans mRNA for complementary codon where GTP-eIF2 anchors PIC to mRNA

Question 41

What happens after GTP-eIF2 hydrolyss?

Answer 41

eIF2-GDP is released, forming the 60S subunitm with aminoacyl site ready for new tRNA

Question 42

EF-1a

Answer 42

Delivers charged tRNA to ribosome in translation.