B: Translation

Question 1

Translation initiation

Answer 1

1. Small ribosomal subunit binds
2. Met-tRNA attaches to start codon on small ribosomal unit.
3. Large ribosomal subunit binds.

Question 2

Translation elongation

Answer 2

1. Aminoacyl-tRNA enters A site next to Met-tRNA and binds to matching codon.
2. Peptide bond forms between adjacent amino acids, so methionine transfers to amino acid in A site.
3. Methionine forms N-terminus, and Val forms C-terminus. New amino acids added will form C-terminus.
4. Once peptide bond is formed, mRNA is pulled forward through ribosome by one codon, so empty tRNA drifts out via E (exit) site. A site is empty so cycle can repeat.

Question 3

Translation termination

Answer 3

Termination
1. Stop codon enters A site.
2. Stop codons are recognized by release factor proteins.
Hydrolyse ester linkage, protein is released.

Question 4

How are amino acids attached to tRNAs? formula

Answer 4

Amino acid + tRNA + ATP + aminoacyl-tRNA –> AMP + 2Pi + charged tRNA-met.