Proteins

Question 1

Protein uses

Answer 1

-collagen-elasticity
-antibodies-immune response
-enzymes
-blood clot-fibrin + platelets
-keratin

Question 2

Proteins contain

Answer 2

H
C
O
S
N

Question 3

Amino acids

Answer 3

-toxic in high amounts
-excess broken down by deamination in liver to urea

Question 4

2 amino acids condensation

Answer 4

Dipeptide-covalent=strong

Question 5

Polypeptide

Answer 5

Many amino acids
Nh2 00000000 COOH

Question 6

Proteins function and structure

Answer 6

Function related to order of amino acids
= must be produced correctly from mRNA

Question 7

Fibrous proteins

Answer 7

Répétitive séquence of amino acids

Insoluble In water

Structured

Question 8

Secondary structure a helix

Answer 8

The chain of amino acids is not straight but twists into a shape called the secondary structure.
The helix is held together by hydrogen bonds between the – NH of one amino acid and the –CO four places ahead of it in the chain.

Question 9

Secondary structure B pleated sheet

Answer 9

Other chains fold in a zig-zag structure.
Hydrogen bonds occur between the –NH group of one amino acid and the –CO group further down the strand.

β bends allows the change of direction of the peptide chain to get a folded structure.

Question 10

Tertiary structure

Answer 10

When coils and pleats start to fold, they form tertiary structures. They are held together by:
• H-bonds =O HN-
• Ionicbonds–NH3-COO-
• Disulphide bridge –CH2S- SCH2-
• BondingbetweenR-groups gives rise to a 3D shape

Question 11

Globular protein

Answer 11

Hydrophobic parts of the R groups move to the centre of the polypeptide to avoid water, whereas hydrophilic parts move towards the water.
These interactions cause the twisting of the amino acid chain which changes the shape of the protein to form globular proteins.
This makes the protein water soluble because water molecules can easily cluster around them.

Question 12

Fibrous vs globular

Answer 12

Fibrous proteins
• Repetitive sequences of amino acids
• Insoluble in water
• Structural
• e.g. collagen
Globular proteins
• Almost spherical in shape
• Soluble in water due to position of hydrophilic/phobic R groups
• 3D shape
• e.g. enzymes

Question 13

Collagen

Answer 13

Collagen molecules are made of repeating sequences of amino acids that form spiral structures.
Collagen protein is made of 3 polypeptide chains wound together like a rope. Hydrogen bonds hold the chains together.
Collagen is a STRUCTURAL protein and can be found in artery walls, tendons and bones (reinforced with calcium phosphate).

Question 14

Haemoglobin

Answer 14

Haemoglobin is a globular protein that has a quaternary structure.
It is made up of two α-globin and two β-globin polypeptide chains (each having it’s own tertiary structure).
The polypeptide chains are held together by similar bonds as the tertiary structure.
The haem area is called a “prosthetic” group. A molecule of oxygen can bind to each haem group (contains iron).

Question 15

Peptidases

Answer 15

• Exopeptidases - hydrolyse peptide bonds on the ends of polypeptides in the stomach
• Endopeptidases – hydrolyse peptide bonds within polypeptides in the stomach
• Dipeptidases – hydrolyse dipeptides membrane bound enzymes in the ileum