BGM1002/L19 Translation II

Question 1

What are ribosomes made of?

Answer 1

Ribonucleoprotein (RNA-protein)

Question 2

How abundant are ribosomes?

Answer 2

10% of total protein
80% RNA

Question 3

Describe the composition of 70S ribosomes.

Answer 3

50S + 30S subunits

Question 4

What does the ‘S’ in 70S stand for?

Answer 4

Svedberg unit
Measure sedimentation rate in a centrifuge thus size and shape

Question 5

Describe the structure of the 50S ribosomal subunit.

Answer 5

31 different L proteins
23S rRNA
5S rRNA

Question 6

Describe the structure of the 30S ribosomal subunit.

Answer 6

21 S proteins
16S rRNA

Question 7

What is required for translation initiation?

Answer 7

Initiation factors IF1, IF2, IF3 and GTP
Initiator tRNA: fMet-tRNA^fMet

Question 8

What is required for translation elongation?

Answer 8

Elongation factors EF-Tu, EF-Ts, EF-G and GTP

Question 9

What is required for translation termination? (2)

Answer 9

Stop codon
Release factors RF1 and RF2

Question 10

What is the name of initiator tRNA in bacteria?

Answer 10

N-formylmethionine (fMet)

Question 11

What happens to methionine once it is removed from the initiator tRNA?

Answer 11

Formyl group transferred to methionine by formyltransferase

Question 12

Which part of the ribosome binds to Shine Dalgarno sequence/ribosome binding site to initiate translation?

Answer 12

30S subunit

Question 13

Where does initiator tRNA bind to initiate transcription?

Answer 13

Start codon AUG

Question 14

Name the 3 sites of the ribosome involved in initiation of translation.

Answer 14

A site: amino acyl site
P site: peptidyl site
E site: exit site

Question 15

What binds to form the 70S ribosomal complex?

Answer 15

50S and 30S ribosomal subunits

Question 16

How is the 30S ribosomal subunit positioned on the 16S rRNA?

Answer 16

Base pairing between Shine Dalgarno sequence and 16S rRNA

Question 17

Where do IF1 and IF3 bind?

Answer 17

30S subunit

Question 18

Where does IF2 bind?

Answer 18

Complex with GTP

Question 19

How is IF3 released from 30S ribosomal subunit?

Answer 19

Charged initiator tRNA binds to mRNA

Question 20

What displaces IF1 and IF2 during initiation? What is produced?

Answer 20

50S ribosomal subunit
GDP + Pi

Question 21

Describe the process of translation elongation. (3)

Answer 21

Aminoacyl tRNA binds to A site
Peptide bond formation
Translocation

Question 22

What is required for delivery of charged tRNA to the A site?

Answer 22

EF-Tu, EF-Ts + GTP

Question 23

What is required for translocation of RNA through ribosomes?

Answer 23

EF-G + GTP

Question 24

What occurs when GTP is hydrolysed in the presence of EF-Tu?

Answer 24

EF-Tu-GDP complex forms

Question 25

How is the EF-Tu-GDP complex broken down?

Answer 25

EF-Ts exchanges GDP for GTP

Question 26

Describe peptide bond formation in translation. (2)

Answer 26

Amino group of aminoacyl-tRNA attacks carbonyl group of ester linkage of peptidyl-tRNA
Deacylated tRNA released

Question 27

What sequences does RF1 recognise?

Answer 27

UAA and UAG

Question 28

What sequences does RF2 recognise?

Answer 28

UAA and UGA

Question 29

What does RF3.GTP do?

Answer 29

Helps RF1 and RF2 conduct termination

Question 30

What is the role of RRF and EF-G?

Answer 30

Promote dissociation of ribosome

Question 31

How is the energy for termination provided?

Answer 31

GTP hydrolysis