26 WJEC Biology AS Level - Marianne Izen - 2nd Edition

Question 1

Describe the secondary structure of protein

Answer 1

This is the shape that the polypeptide chain forms as a result of hydrogen bonding between the -O on -CO groups and the -H on-NH groups in the peptide bonds along the chain.

This causes the long polypeptide chain to be twisted into a 3D shape.

The spiral shape is the a-helix.

Another, less common, arrangement is the ẞ-pleated sheet.

The protein keratin has a high proportion of a-helix and the protein fibroin, in silk, has a high proportion of ẞ-pleated sheet.

Question 2

Answer 2

A - a- 1,4- glycosidic

B - ester

C - peptide

Question 3

Answer 3

A - tertiary

B - secondary

C - primary

D - quarternary

Question 4

Describe the primary structure of proteins

Answer 4

This is the order of the amino acids in a polypeptide chain.

Polypeptides have up to 20 different types of amino acid.

They can be joined in any number, order and combination, so there is a huge number of possible polypeptides.

The primary structure is determined by the base sequence on one strand of the DNA molecule.