Translation

Question 1

What are the main components of a ribosome and their functions?
A:

Answer 1

Two unequal subunits: small subunit and large subunit

Small subunit: Contains decoding centre where codon/anticodon binding occurs

Large subunit: Contains peptidyl transferase centre (PTC) where peptide bond formation occurs
Contains three tRNA binding sites (A, P, and E) at the subunit interface
PTC is RNA-rich and peptide bond formation is RNA-catalysed

Question 2

What are the three tRNA binding sites on a ribosome and what binds to each?

Answer 2

A site (Aminoacyl): Holds incoming aminoacyl-tRNA
P site (Peptidyl): Holds tRNA with growing peptide chain
E site (Exit): Holds deacylated tRNA before it exits

Question 3

where does ribosome synthesis occur in eukaryotes?
*rRNA transcription and early rRNA processing steps

Answer 3

nucleoli

Question 4

What are the main steps in the translation elongation cycle?

Answer 4

1. Aminoacyl-tRNA binding
2. Peptide bond formation
3. Translocation of the ribosome along the mRNA

Question 5

when is the tRNA released from the E site?

Answer 5

During this process, tRNA is released from the E site when new aminoacyl-tRNA binds to the A site

Question 6

what are the adjacent binding sites of tRNA binding during translation?

Answer 6

A and P site
P and E site

Question 7

Which GTPases are involved in translation elongation and what are their roles?
*GTP is hydrolysed into GDP

Answer 7

1. EF1A (EF-Tu in prokaryotes):
   - Brings aminoacyl-tRNA to the ribosome
2. EF2 (EFG in prokaryotes):
   - Required for translocation

Question 8

How many GTPases are required per translation elongation cycle?

Answer 8

2
(EF1A and AF2)

Question 9

Describe the translation elongation cycle

Answer 9

Aminoacyl-tRNA Binding:
EF1A (called EF-Tu in prokaryotes) brings the aminoacyl-tRNA to the ribosome
This GTPase delivers the tRNA to the A site
When a new aminoacyl-tRNA enters the A site, any tRNA in the E site is released

Peptide Bond Formation:
Occurs at the peptidyltransferase center (PTC) on the large subunit
This is an RNA-catalyzed reaction (the PTC is RNA-rich)
The growing peptide chain is transferred from the P site tRNA to the amino acid on the A site tRNA

Translocation:
Requires another GTPase called EF2 (EFG in prokaryotes)
The ribosome moves along the mRNA

Question 10

How does prokaryotic translation initiation differ from eukaryotic initiation?

Answer 10

Prokaryotic:
Uses Shine-Dalgarno sequence that base-pairs with 16S rRNA
Direct recognition of start codon

Eukaryotic:
Involves cap-binding complex (CBC)
Scanning mechanism from 5’ end
Requires Kozak sequence context
More complex process with additional factors

Question 11

What are the stages of translation?

Answer 11

Initiation

Elongation

Termination

Question 12

What GTPases function in the process of translation?

Answer 12

Guanosine tri phosphate

Elongation
EF1A - binds to charged tRNA and brings them to the ribosomes - hydrolyses GTP after the tRNA has been selected

EF2 - drives the translocation process where the ribosome moves along the mRNA

so they are 2 GTPases required for each cycle of translation elongation

Initiation
EF2 - bind to initiator tRNA and brought to the P site (not the A site) on the ribosome. / then hydrolyses GTP and is released

Termination
RF1 - binds to the A site to trigger termination

RF3 - triggers the release of the terminator factors / hydrolyses GTP / and then allows ribosome complex to be recycled.