3.7 Types of proteins

Question 1

What are the three types of proteins?

Answer 1

Globular
Conjugated
Fibrous

Question 2

Features of globular proteins:

Answer 2

compact
water soluble (essential for function)
roughly spherical in shape
form when proteins fold into their tertiary structures where the HYDROPHOBIC R groups are kept away from the aqueous environment
HYDROPHYLLIC R groups on the outside

Question 3

Features of conjugated proteins:

Answer 3

Globular proteins that contain a non-protein component = a prosthetic group

Question 4

What is a protein without a prosthetic group called?

Answer 4

A simple protein

Question 5

Different types of prosthetic groups:

Answer 5

Lipids = lipoproteins
Carbohydrates = glycoproteins
Metal ions/molecules derived from vitamins

Question 6

Example of a prosthetic group

Answer 6

Haem groups containing Fe II ions found in haemoglobin

Question 7

Features of fibrous proteins:

Answer 7

long, insoluble molecules
high number of amino acids with hydrophobic R groups
limited range of amino acids with small R groups
Amino acid sequence is repetitive = organised structure
form strong, long molecules which aren’t folded into complex 3 dimensional shapes
Stabilised with hydrogen bonds

Question 8

Why are small R groups important in fibrous proteins?

Answer 8

Allows them to be close together to twist together and form a VERY STRONG structure

Question 9

Examples of globular proteins:

Answer 9

Insulin

Question 10

Examples of conjugated proteins:

Answer 10

Haemoglobin
Catalase

Question 11

Examples of fibrous proteins:

Answer 11

Keratin
Elastin
Collagen

Question 12

Structure/function of insulin:

Answer 12

Hormone involved in regulation of blood glucose concentration
Transported in bloodstream so needs to be soluble
Have to fit in specific receptors on cell membranes (need precise shapes)

Question 13

Structure/function of haemoglobin:

Answer 13

Quaternary protein made from 4 polypeptides (2 alpha, 2 beta subunits) - each subunit contains prosthetic haem group with Iron II ions which combine with the oxygen to transport it
Enables oxygen to be transported around the body and released when needed

Question 14

Structure/function of catalase:

Answer 14

Enzyme - catalyses reaction and is specific to reaction
Quaternary protein containing 4 haem prosthetic groups
Iron II ions allows it to interact with hydrogen peroxide = speeds up its breakdown (common by-product of cellular chemical reactions that can damage cells if not broken down)

Question 15

Structure/function of keratin:

Answer 15

Group of fibrous proteins present in hair, skin and nails
Large proportion of sulfur-containing amino acid (cysteine)
This results in strong, disulphide bonds = strong, inflexible and insoluble
Degree of disulphide bonds determines flexibility:
- Hair = more flexible
- Nails = less flexible

Question 16

Why is there an unpleasant smell when hair or skin is burnt?

Answer 16

Due to large quantity of sulfur in disulphide bonds

Question 17

Structure/function of elastin:

Answer 17

Fibrous protein found in elastic fibres (with small protein fibres)
Elastic fibres are present in blood vessel walls + alveoli (flexibility)
Quaternary protein made from many stretchy molecules called tropoelastin

Question 18

Structure/function of collagen:

Answer 18

Fibrous protein
Connective tissue - skin, tendons, ligaments, nervous system
Number of different forms - all made of 3 polysaccharides wound togteher in a long, rope-like, strong structure
Provides flexibility