3: Types of proteins

Question 1

What are the two main groups of protein?

Answer 1

Globular proteins and fibrous proteins

Question 2

What are globular proteins?

Answer 2

Compact, water soluble, spherical proteins. Form when proteins fold into their tertiary structure in such a way that the hydrophilic R-groups on the amino acids are on the outside of the protein (so are therefore soluble)

Question 3

What is insulin?

Answer 3

A globular protein. It is a hormone involved in regulation of blood glucose concentration

Question 4

What are conjugated proteins?

Answer 4

Globular proteins that contain a non-protein component (prosthetic group). Proteins without prosthetic groups are called simple proteins

Question 5

Give an example of a prosthetic group

Answer 5

Haem groups. Contain an iron (II) ion. Haemoglobin contains haem groups

Question 6

What is haemoglobin?

Answer 6

Red, oxygen-carrying pigment found in red blood cells. Quaternary protein made from four polypeptides (two alpha and two beta subunits). Each subunit contains a prosthetic haem group. The iron (II) ions present in the haem groups are each able to combine reversibly with an oxygen molecule which is what enable haemoglobin to transport oxygen around the body

Question 7

What are fibrous proteins?

Answer 7

Formed from long, insoluble molecules. Contain a limited range of amino acids, usually with small R-groups. The amino acid sequence is usually quite repetitive leading to very organised structures

Question 8

Give three example of fibrous proteins

Answer 8

Keratin, elastin and collagen

Question 9

What is keratin?

Answer 9

Group of fibrous proteins present in hair, skin and nails. It has a large proportion of sulfur-containing amino acid, cysteine resulting in many strong disulfide bridges forming strong, inflexible, insoluble materials

Question 10

What is elastin?

Answer 10

A fibrous protein found in elastic fibres. Elastic fibres are present in the walls of blood vessels - they give these structures flexibility. Elastin is a quaternary protein made from many stretchy molecules called tropoelastin

Question 11

What is collagen?

Answer 11

A fibrous protein. Connective tissue found in skin, tendons and ligaments. Made up of three polypeptides wound together in a long, strong structure. Flexible