June 2018 QP Paper 2 AS

Question 1

Compare the properties and functions of fibrous and globular proteins.

Answer 1

Properties:

Fibrous proteins are rod-like in shape, while globular proteins are sphere-like. In addition, fibrous proteins are insoluble as a result of numerous hydrophobic side groups, while globular proteins have hydrophilic groups on their outside, making them soluble.

Functions:

Fibrous proteins have structural roles in the body, such as collagen in bones and keratin in hair. In contrast, globular proteins have physiological or metabolic functions, such as hormones like insulin, or enzymes like protease.

Question 2

Describe the food test for proteins.

Answer 2

1. Add some of the food sample to a test tube and add equal volume of sodium hydroxide solution.
2. Add a few drops of copper sulfate to solution in test tube and mix.
3. A positive test will turn the colour of solution to purple, compared to a negative test turning blue.

Question 3

What is the difference between conjugated and globular proteins?

Answer 3

Conjugated proteins are globular proteins with a prosthetic group.