58 WJEC Biology AS Level - Study And Revision Guide - Neil Roberts (1.5 Nucleic Acids And Their Functions)

Question 1

Describe the steps in translation.

Answer 1

1. Initiation: ribosome attaches to the START codon.
2. tRNA molecule with a complementary anticodon to the first codon, binds to the first attachment site on the ribosome.
3. A second tRNA molecule joins to the second attachment site, and a ribosomal enzyme catalyses the formation of a peptide bond between the two amino acids. This is known as elongation.
4. The first tRNA molecule is released and the ribosome now moves one codon along the mRNA, which exposes a free attachment site and another tRNA molecule joins and the process is repeated.
5. This repeats until a STOP codon is reached, when the polypeptide is released. This is called termination.
6. Usually several ribosomes bind to a single mRNA strand at the same time. This is called a polysome.

Question 2

Draw a diagram of translation.

Answer 2

Question 3

What does translation produce?

Answer 3

Translation produces a polypeptide.

Question 4

What is post-translational modification?

Answer 4

After a polypeptide is made, further modification is needed in order to produce a protein with a secondary, tertiary or quaternary structure.

Modification also occurs to produce molecules such as glycoproteins, lipoproteins, and complex quaternary structures such as haemoglobin.

Question 5

Where does post-translational modification occur?

Answer 5

This modification occurs within the Golgi body.

Question 6

What is necessary to form haemoglobin?

Answer 6

To form haemoglobin, two alpha chains and two beta chains (coded by two different genes) need to be assembled together with iron as a prosthetic group.

Question 7

Answer 7

Question 8

Answer 8