Translation

Question 1

info in mRNA to make protein is in…

Answer 1

Open Reading Frame

Question 2

Trp unusual amino acid because?

Answer 2

Only encoded by 1 triplet

Question 3

How much of ribosomal mass is rRNA?

Answer 3

2/3

Question 4

In bacteria what are rRNAs called? (named after density centrifugation)

Answer 4

5S, 16S, 23S

Question 5

What does 23S do?

Answer 5

23S gives core peptidyl transferase activity of ribosome (ie. peptide bond forming)

Question 6

What does tRNA look like?

Answer 6

see notes for diagram

Question 7

What enzyme attaches amino acids to tRNA and what bond does it catalyse formation of?

Answer 7

Aminoacyl-tRNA synthetase

Ester bond between carboxyl group on amino acid and 2’/3’ hydroxyl group on 3’ terminal adenosine of tRNA

Question 8

What is the main cause of tRNA size differences?

Answer 8

The variable/extra arm, 4-21 bases long

Question 9

How many ORFs can prokaryotes have and what does this mean?

Answer 9

> 1

Multiple proteins can be translated from different ORFs on one mRNA

Question 10

What is the Shine-delgarno sequence and how far is it from the AUG codon?

Answer 10

AGGAGG
6-8 nt before AUG codon
Binds to 16S bacterial RNA in the small subunit

Question 11

What is coupled bacterial translation?

Answer 11

When it occurs before transcription is finished

Question 12

What is the difference with eukaryotic translation?

Answer 12

Each mRNA only has 1 ORF, transciption and processing of mRNA in nucleus means transciption and translation can’t be coupled

Question 13

Give 4 steps of prokaryotic translation initiation

Answer 13

1) 16S rRNA binds and helps position 30S ribosomal subunit to help bind initiator codon, further helped by Initiator Factor 3 (IF3) and more IFs
2) First initiator tRNA= fMet tRNA (formylated methionine-tRNA)
3) 50S subunit recruited
4) GTP hydrolysis by IF2 and release of IFs

Question 14

What is different about eukaryotic initiation?

Answer 14

40S subunit interacts with eIFs (eukaryotic initiation factors) to recognise and be recruited to the 5’ capping structure on mRNA
Complex scans to AUG (no Shine-Delgarno), releases eIFs , 40S binds 60S and elongation proceeds

Question 15

Transcription start site is not the same as…

Answer 15

Translation start site

Question 16

How does elongation differ in eukaryotes and prokaryotes?

Answer 16

Trick q, its the same

Question 17

What are the main catalytic sites of the ribosome?

Answer 17

P site, A site, E site

Question 18

What do these sites do?

Answer 18

Facilitate amino-acyl tRNA arrival, peptide bond formation via peptidyl transferase and tRNA exit

Question 19

Elongation is helped by accessory protein… (not specific just broad term for them)

Answer 19

Elongation factors (EF) prokaryotes and eEF in eukaryotes

Question 20

What are stages of elongation?

Answer 20

1) Complex of EF and GTP and aminoacyl-tRNA enters ribosome at A site
2) If codon:anticodon recognition ribosome changes conformation and hydrolyses GTP
3) EF releases amino-acyl tRNA and leaves
4) Free amino-acyl end of tRNA moves into peptidyltransferase centre of large ribosome and peptide bond forms between aminoacyl compotents of tRNA in A and P site
5) specific type of elongation factor EF-G:GTP gets recruited, GTP gets hydrolysed, aids release of tRNA from P site

Question 21

What happens if there is a termination codon in the A site?

What is eg. of termination codon?

Answer 21

Release factors 1 and 2 (RF1/2) recognise termination codon eg. UAA and stimulate ribosome dissociation
Ribosomal components can then reassemble for another round of translation