3.7- Types Of Proteins

Question 1

What are globular proteins?

Answer 1

• compact
• water soluble
• roughly spherical in shape.

Formed when proteins fold into their tertiary structures in such a way that the hydrophobic R-groups on the amino acids are kept away from the aqueous environment.
Solubility is important because they regulate many necessary processes such as chemical reactions, immunity, muscle contraction.

Question 2

Insulin

Answer 2

• globular protein
• hormone that regulates blood glucose concentration.
• transported in blood so has to be soluble.
• have precise shapes as they need to fit into specific receptors on cell surface membranes.

Question 3

What are conjugated proteins?

Answer 3

• globular proteins that contain a prosthetic group (non-protein component).
• Haem groups are examples of prosthetic groups, they contain an iron ion (Fe2+).

Question 4

Haemoglobin

Answer 4

Conjugated protein.

• quaternary protein made from 4 peptides: two alpha +two beta.
• each subunit has a prosthetic haem group.
• the iron ions present in haem groups can combine reversibly with an oxygen molecule = allows transportation.

Question 5

Catalase

Answer 5

• an enzyme.
• quaternary protein with 4 prosthetic haem groups.
• iron ions allow it to interact with hydrogen peroxide and speed up its breakdown.
• hydrogen peroxide= byproduct of metabolism which damages cells if allowed to accumulate however catalase stops this.

Question 6

What are fibrous proteins?

Answer 6

• formed from long insoluble molecules.
• insoluble due to the presence of a high proportion of amino acids with hydrophobic R-groups in their primary structures.
• amino acid sequence is usually quite repetitive so leads to very organised structures.
• make strong, long molecules which are not folded into complex 3D shapes like globular proteins.

Question 7

Keratin

Answer 7

• present in hair, skin, nails.
• large proportion of cysteine so results in many strong disulfide bonds.
• strong, inflexible and insoluble.
• degree of disulfide bonds determines flexibility
• unpleasant smell when burnt is due to the large quantities of sulfur present.

Question 8

Elastin

Answer 8

• fibrous protein found in elastic fibres which are present in the walls of blood vessels and alveoli in lungs; give these structures the flexibility to expand and return to normal size.
• quaternary protein. Made by linking many soluble molecules called tropoelastin. This makes a large, insoluble, stable and cross-linked structure.

Question 9

Collagen

Answer 9

• connective tissue found in skin, tendons, ligaments and the nervous system.
• made up of 3 polypeptides wound in a long and strong rope like structure.
• has flexibility.

Question 10

What are essential and non- essential amino acids?

Answer 10

20 different amino acids are commonly found in cells.

• 5 of these are considered non-essential as the body is able to make them from other amino acids.
• 9 are essential and can only be obtained from what we eat.
• a further 6 are considered conditionally essential as they are only needed by infants and growing children.