Chapter 3.13 - Protein synthesis: Translation

Question 1

What is translation?

Answer 1

The process by which the complementary code carried by mRNA is decoded by tRNA into a sequence of amino acids, this occurs at a ribosome

Question 2

What are ribosomes composed of?

Answer 2

A large and small subunit which are composed of proteins and a form of RNA, rRNa

Question 3

What is the purpose of rRNA in ribosomes?

Answer 3

They maintain the structural stability of the protein synthesis sequence and plays a biochemical role in catalysing the reaction

Question 4

What are the steps in translation?

Answer 4

1. The ribosome attaches to the mRNA strand at a start codon
2. A tRNA molecule, carrying a specific amino acid and with an anticodon that is complementary to the start codon, binds to the mRNA
3. A second tRNA molecule with an anticodon complementary to the next mRNA codon, and also carrying a specific amino acid, attaches to mRNA
4. The amino acids carried by the first two tRNA molecules are linked together via a peptide bond using ATP
5. The first tRNA molecule detaches from mRNA and is free to collect another amino acid for future use
6. The ribosome moves along mRNA, allowing another tRNA molecule, which carries the next amino acid, to bind to the next codon on mRNA
7. The process from step 4 to 6 is repeated, which elongates the polypeptide chain
8. At any point during this process, two tRNA molecules can be attached to the ribosome.
   The sequence continues until the ribosome reaches a stop codon on mRNA
9. The completed polypeptide chain detaches from the ribosome

Question 5

What happens to the structure of the amino acid chain as it elongates?

Answer 5

As the amino acids are joined together forming the primary structure of the protein, they fold into secondary and tertiary structure. The protein may undergo further modification at the Golgi apparatus before it fully functional and ready to carry out its role

Question 6

What determines the folding and bonds formed in proteins?

Answer 6

The sequence of amino acids in the primary structure

Question 7

How can multiple identical polypeptides be synthesised simultaneously?

Answer 7

Many ribosomes can follow on the mRNA behind the first