Biological molecules - Proteins and Enzymes

Question 1

What is the function of haemoglobin as a protein

Answer 1

Transports oxygen

Question 2

What is the function of antibodies as a proein

Answer 2

Defends the body against infection

Question 3

What is the function of enzymes as a protein

Answer 3

Biological catalysts

Question 4

What is the function of actin + myolin as a protein

Answer 4

involved in muscle contraction

Question 5

How are dipeptides formed

Answer 5

A condensation reaction between 2 amino acids forms a peptide bond

Question 6

How are polypeptides formed

Answer 6

Many peptode bonds between many amino acids

Question 7

What is the primary structure

Answer 7

Number and sequence of amino acids in a polypeptide chain

Question 8

What is the secondary structure

Answer 8

• The folding of the polypeptide chain into an alpha helix or a beta pleated sheet
• Structure is maintained by hydrogen bonds between the NH group of one amino acid and the C=O bond

Question 9

What is the tertiary structure

Answer 9

The further folding of the polypeptide chain into a specific 3D shape

Question 10

What are the 3 different types of bonds between R groups in the tertiary structure

Answer 10

• Hydrogen Bonds which are weak bonds but many together are strong
• Ionic Bonds, also weak bonds which form between oppositely charged R groups
• Disulphide Bridges - Covalent bonds which form between sulphur containing R groups

Question 11

What is the quaternary structure

Answer 11

More than one polypeptide chain joined together

Question 12

Biuret test

Answer 12

• Add Biuret solution to a sample
• For positive test result there will be a colour change from blue to purple/lilac

Question 13

Describe the induced fit model

Answer 13

• Enzyme-substrate complex formed between substrate and enzyme active site
• Binding substrate induces the change in shape of the active site so it becomes complementary to the substrate
• This puts pressure on the bonds in the substrate which cause them to break more easily
• When producs leave, the active site returns to its previous shape allowing it to bind to another substrate

Question 14

Effect of temperature on rate of enyme activity

Answer 14

• As temperature increases to optimum, enzyme and substrate molecules have more KE and are more likely to form enzyme-substrate complexes
• Beyond optimim - hydrogen bonds holding tertiary structure start to break which changes shape of active site so no longer specific

Question 15

Effect of pH on rate of enyme activity

Answer 15

• Up to optimum - rate of enzyme activity increases
• After optimum - Hydrogen nd ionic bonds in the tertiary structure are broken. Active site changes shape. No enzyme substrate complexes are formed

Question 16

Effect of substrate concentration on rate of enyme activity

Answer 16

• As substrate conc increases the rate of reaction increases and then plateaus
• RoR is low at low substrate concentrations as the substrate is the limiting factor
• As substrate conc increases the substrate is no longer the limiting factor and therefore RoR increases
• At high substrate cones all enzyme sites are filled so no more enzyme substrate complexes can form. The concentration of enzymes is now the limiting factor

Question 17

Effect of enzyme concentration on rate of enzyme activity

Answer 17

• The more enzymes in a solution, the more likely they are to collide with a substrate and form an enzyme substrate complex
• Increasing the enzyme concentration increases the rate of reaction
• If the amount of the substrate becomes limiting, increasing enzyme concentration will have no effect on the rate of reaction

Question 18

What are the 2 types of inhibitors

Answer 18

• Competitive inhibitors
• Non-competitive inhibitors

Question 19

Effect of a competitive inhibitor rate of enzyme activity

Answer 19

• They have similar structures to the substrates
• They fit into the active site but do not react
• They prevent the normal substrate from binding and hence slow the rate of reaction as less enzyme substrate complexes can be formed

Question 20

Effect of a non-competitive inhibitor on rate of enzyme activity

Answer 20

• They bind to a site on the enzyme other than the active site
• They alter the shape of the active site so that the substrate cannot fit
• No more enzyme substrate complexes can be formed and the rate of reaction is decreased