proteins

Question 1

Erythrocytes contain haemoglobin, which is a globular protein.Blood vessel walls contain collagen, which is a fibrous protein.
Describe the differences between globular and fibrous proteins using haemoglobin and collagen as examples.
In your answer you should refer to collagen and haemoglobin.

Answer 1

Globular
ball shaped or spherical
hydrophilic , R groups on outside, hydrophobic R groups on inside
form H-bonds with water so
soluble
haemoglobin transports oxygen / CO2
haemoglobin contains prosthetic group haem Fe2+
(to allow oxygen to be carried) ;
(polypeptide chains within) haemoglobin have tertiary
structure (in a ball shape) ;
Fibrous
linear / long (chain)
(chains can) form (H) bonds with adjacent chains
(within a molecule) ;
insoluble / few hydrophilic groups ;
strong / provide strength ;
have structural role ;
collagen has high proportion of glycine , so chains can
lie close together
collagen forms , crosslinks / covalent bonds between
molecules
crosslinks / ends of molecules, are staggered to avoid weak points
collagen forms part of , tendon / cartilage / bone

Question 2

State one property of collagen that makes it a useful component of blood vessel walls.

Answer 2

strength / toughness / insolubility ;

Question 3

Describe the structure of the collagen molecule.

Answer 3

peptide bonds between amino acids in polypeptide
every 3rd amino acids is same - glycine ;
spiral / helix (left-handed)
glycine / small R group , allows closeness /
twisting (of polypeptide chains) ;
three polypeptide chains ;
hydrogen / H , bonds between (polypeptide)
chains ;
no / few, hydrophilic (R) groups on outside (of
molecule) ;
(adjacent molecules joined by) crosslinks ;
crosslinks / ends of molecules , being
staggered ;
fibril ;

Question 4

State one function of haemoglobin.

Answer 4

transport / AW , of, oxygen / O2 ;

Question 5

Describe three other ways in which the structure of haemoglobin differs from that of collagen.

Answer 5

haemoglobin (has / is):
globular ;
hydrophobic (R) groups on inside / hydrophilic
(R) groups on outside ;
4 , chains / sub-units / polypeptides ;
idea that subunits are (two) different types ;
α / alpha , helix ;
idea that proportion of glycine similar to that ,
of other amino acids / in other proteins ;

Question 6

Peptide bond (3)

Answer 6

• bond between two amino acids
• between amino group and carboxyl group
• formed through condensation/ dehydration reaction

Question 7

Secondary structure of protein

Answer 7

• partially 3D structure maintained by hydrogen bonds
• alpha helix
• beta pleated

Question 8

Tertiary structure

Answer 8

• interactions between the R groups to create a 3D shape
• hydrophobic interactions
• disulphide bonds
• iconic bonds

Question 9

Quaternary structure and example

Answer 9

• more than one tertiary structures fitted together
• weak R group interactions
• Van de Waal forces between sub units
• eg Haemoglobin

Question 10

Describe Haemoglobin

Answer 10

• globular
• 4 subunits
• 2 beta chains, 2 alpha chains
• 4 haem groups
• transports oxygen in the blood; haem group contain iron binds to oxygen

Question 11

Insulin

Answer 11

Hormone that controls blood glucose concentration

Globular

Question 12

How are proteins used in signalling

Answer 12

Hormones
Act as chemical messengers at receptors of cells

Enzymes
Change receptors

Question 13

Keratin

Answer 13

Fibrous

Structural protein

Found in; hooves, hair, scales, nails