Translation - lecture 4

Question 1

What does aatRNA stand for?

Answer 1

Aminoacyl - transfer RNA (basically tRNA)

Question 2

What does it mean when tRNA is ‘charged’?

Answer 2

Coupled with the correct amino acid

Question 3

What is aminoacylation?

Answer 3

Covalently attach the correct amino acid to the tRNA ( as specified by the anticodon)

Question 4

What does aaRSs stand for?

Answer 4

Aminoacyl-tRNA synthetases

Question 5

How do aaRSs select the right tRNA to be acylated?

Answer 5

Recognisng specific rTNA identifiers present on the acceptor step and anticodon loop. Highly conserved sequences i.e, G1,G2,G3.

Question 6

How does the tRNA attach to the ribosome?

Answer 6

Ribosomes select aa-tRNA based only on there codon - anticodon interactions

Question 7

What ribosomes are made of?

Answer 7

Made of rRNA and ribosomal proteins. have 2 subunits ; large and small. Subunits are not self assembling. combine only in presence of mRNA and aatRNA

Question 8

What are the 4 steps involved in chain initiation?

Answer 8

• Formation of 43S pre- initiation complex
• formation of the initiation complex
• positioning at the start codon
• association of large subunit

Question 9

What are the 3 steps of polypeptide synthesis?

Answer 9

1 - chain initiation
2 - chain elongation
3 - chain termination

Question 10

What does elF stand for?

Answer 10

Elongation factor

Question 11

Mechanism of forming the 43S pre - ignition complex

Answer 11

40S - elF3 already bound with elF1A . Then elF2 binds coupled with tRNA via GTP. elf5 also binds

Question 12

Binding the 43S complex to the mRNA

Answer 12

elF4 complex binds to the mRNA which causes the poly A tail to bind to this too.
pre- initiation complex binds to the elF4 complex

4E,4G and 4A bind first then 4B binds

Question 13

Positioning the initiation complex at the start codon

Answer 13

• initiation complex unwinds mRNA using elF4 helicase

- initiation complex stops at the AUG start site

Question 14

Association of the large subunit (60S)

Answer 14

irreversible GTP hydrolysis mediates the association of the 60S - elF6 to the small subunit by the action of elF5.
factor displacement

Question 15

Whats happened after setting up the initiation complex?

Answer 15

ribosome formed with a methionine at the P position

Question 16

First step of chain elongation

Answer 16

aatRNA binding. Binds to the A site on the ribosomes . This is mediated by ef1

Question 17

Second step of chain elongation

Answer 17

GTP hydrolysis induces conformational change in the ribosome . EF1 dissociates.

Question 18

Third step of chain elongation

Answer 18

Peptide bond formation. amino acid from P transferred to form peptide bond on the A site

Question 19

fourth step of chain elongation

Answer 19

GTP hydrolysis moves the tRNAs left , positioning in the E and P sites instead

Question 20

Termination of the chain

Answer 20

Release factors bind to stop condons.

This induces peptidyl transferase to transfer water instead of aatRNA. Release

Question 21

What antibiotics inhibit translation in prokaryotes?

Answer 21

streptomycin and chloramphenicol

Question 22

What antibiotics inhibit translation in eukaryotes

Answer 22

cycloheximide

Question 23

What antibiotics inhibit translation in both prokaryotes and eukaryotes?

Answer 23

puromycin

Question 24

what enzyme catalyses the formation of a peptide bond?

Answer 24

peptidyl transferase