Unit 1: Translation

Question 1

What is a codon ?

Answer 1

3 consecutive bases that specify a single amino acid

Question 2

Codons are degenerate, what does this mean ?

Answer 2

That multiple codons can code for the same amino acid

Question 3

What is a reading frame ?

Answer 3

• The way nucleotides in mRNA are grouped into codons (sets of three) for translation into a protein
• Different codons can be read depending on start point for rf

Question 4

What is an anticodon ?

Answer 4

A triplet of bases that is complementary to codon on mRNA

Question 5

On a tRNA molecule, where does the amino acid attach ?

Answer 5

• At the top
• 3’ end

Question 6

What are the 3 sites in a ribose (all included in the large subunit) ?

Answer 6

• E site
• P site
• A site

Question 7

What is the function of the P site ?

Answer 7

• Holds the tRNA with growing polypeptide attached

Question 8

What is the function of the E site ?

Answer 8

• It holds a tRNA that will exit

Question 9

What is the function of the A site ?

Answer 9

• It holds an aminoacyl tRNA

Question 10

Explain the elongation cycle (5)

Answer 10

1) Aminoacyl tRNA binds to A site with help of EF1 which hydrolyses GTP to GDP +pi to release energy
2) This changes conformation of EF1
3) Peptide bond forms between amino acids with help of peptidyl transferase
4) Translocation occurs and moves ribosome to next codon
5) This is repeated until stop codon is reached

Question 11

What is the most common start codon ?

Answer 11

AUG

Question 12

Explain the process of translation initiation (6)

Answer 12

1) Small ribosomal subunit binds near the 5’ cap
2) Start codon AUG is recognised
3) Initiator tRNA binds to P site on ribosome
4) Once initiator tRNA complex is bound to start codon, large ribosomal subunit will bind
5) This completes the ribosome structure
6) RIbosome also requires GDP and elF2 to start elongation

Question 13

Explain the process of translation termination (4)

Answer 13

1) When ribosome reaches stop codon on mRNA, A site of ribosome accepts a protein called a release factor instead of tRNA
2) Release factor hydrolyses bond between tRNA in the P site and the last amino acid of the polypeptide chain
3) Polypeptide is freed from the ribosome
4) Ribosomal subunits and other components dissemble

Question 14

What are 4 example of antibiotics that target translation ?

Answer 14

1) Streptomycin
2) Chloramphenicol
3) Erythromycin
4) Tetracycline