Polypeptide synthesis - translation

Question 1

Why is tRNA so specific?

Answer 1

There are about 60 different tRNAs therefore each amino acid has one or more tRNA molecule. Particular tRNA has a specific anticodon and attaches to a specific amino acid.

Question 2

How are proteins synthesised into a polypeptide after mRNA has passed out of the nuclear pore?

Answer 2

• A ribosome becomes attached to the starting codon on the mRNA.
• tRNA molecule with the complementary anticodon sequence moves to the ribosome and pairs up with the codon on the mRNA and this tRNA will carry a specific amino acid.
• The ribosome moves along the mRNA, bringing 2 tRNA along with it at a time.
• The 2 amino acid on the tRNA will be joined together by a peptide bond using an enzyme and ATP which is hydrolysed to provide the required energy.
• The ribosome will move to the 3rd codon and it will be linked with the previous 2 amino acids.
• As this happens, the first tRNA is released from its amino acid and is free to collect another amino acid from the amino acid pool in the cell.
• The process continues until a long chain of polypeptide is formed and it stops when it reaches the stop codon. At this point, the ribosome, mRNA and tRNA all separate and the chain is complete.

Question 3

What happens after when the long chain of polypeptide if formed?

Answer 3

• The polypeptide is coiled or folded, producing a secondary structure.
• The secondary structure is folded forming a tertiary structure.
• Different polypeptide chain along with any non-protein groups are linked to form the quaternary structure.