3.7 Types of proteins

Question 1

What are the two main groups of proteins? (2 marks)

Answer 1

Globular and fibrous

Question 2

Describe the tertiary structure of globular proteins. (1 mark)

Answer 2

The hydrophobic R-groups on the amino acids are kept away from the aqueous environment, and the hydrophilic R-groups are on the outside of the protein.

Question 3

Are globular proteins soluble in water, why/why not? (2 marks)

Answer 3

Yes, globular proteins are soluble in water, due to the hydrophobic R-groups being kept on the inside of the molecule and the hydrophilic R-groups being kept on the outside.

Question 4

State three main characteristics of globular proteins. (3 marks)

Answer 4

Compact
Roughly spherical shape
Water soluble

Question 5

Give an example of a globular protein. (1 mark)

Answer 5

Insulin
Haemoglobin
Catalase

Question 6

Why is it important that globular proteins are water soluble, use insulin as an example. (1 mark)

Answer 6

Hormones are transported in the blood, so need to be soluble.

Question 7

What is a conjugated protein? (2 marks)

Answer 7

A globular protein that contains a prosthetic group.

Question 8

What is a prosthetic group? (1 mark)

Answer 8

A non-protein component.

Question 9

Give 2 examples of prosthetic groups. (2 marks)

Answer 9

Lipid
Carbohydrate
Metal ions

Question 10

Why is haemoglobin a conjugated protein? (1 mark)

Answer 10

It contains haem prosthetic groups.

Question 11

Describe the structure of haemoglobin. (2 marks)

Answer 11

2 alpha and 2 beta subunits
Each subunit contains a prosthetic haem group.

Question 12

What prosthestic group does catalase contain? (1 mark)

Answer 12

Haem

Question 13

What enables catalase to interact with hydrogen peroxide and speed up its breakdown. (1 mark)

Answer 13

The iron II ions in the haem prosthetic groups.

Question 14

What does catalase speed up the breakdown of? (1 mark)

Answer 14

Hydrogen peroxide

Question 15

What is a fibrous protein? (1 mark)

Answer 15

They are formed from long, insoluble molecules, that are string. They do not fold into complex 3D shapes.

Question 16

Explain why the structure of fibrous proteins is long and organised. (3 marks)

Answer 16

There is a high proportion of amino acids with hydrophobic R-groups in their primary structures.
Contain a limited range of amino acids with small R-groups.
The amino acid sequence in the primary structure is repetitive.

Question 17

Give 3 examples of fibrous proteins. (3 marks)

Answer 17

Keratin
Elastin
Collagen

Question 18

Where us keratin found in the body? (1 mark)

Answer 18

Hair, skin, nails

Question 19

Where is elastin found in the body? (1 mark)

Answer 19

Walls of blood vessels and in the alveoli in the lungs.

Question 20

Where is collagen found in the body? (1 mark)

Answer 20

Connective tissue: skin, tendons, ligaments, nervous system

Question 21

What makes keratin so strong? (2 marks)

Answer 21

Contains a large proportion of the sulfur containing amino acid, cysteine.
This results in strong disulfide bridges forming.

Question 22

Why are nails less flexible than hair? (1 mark)

Answer 22

There are more disulfide bridges in the keratin in the nails.

Question 23

Describe the structure of elastin. (3 marks)

Answer 23

Many stretchy molecules called tropoelastin are linked to form a large, insoluble, stable, cross-linked structure.

Question 24

Why is elastin stretchy? (2 marks)

Answer 24

It is made up of many tropoelastin molecules that are able to stretch and recoil without breaking.

Question 25

Describe the basic structure of collagen. (1 mark)

Answer 25

Three polypeptide chains wound around each other in a triple helix structure to form a tough, rope-like protein.