Paper 1 - Proteins and Enzymes

Question 1

What are proteins?

Answer 1

Polymers made up of one or more chains of amino acid monomers

Question 2

Amino acid structure

Answer 2

amino group - side chain - carboxyl group

Question 3

What is a dipeptide ?

Answer 3

2 amino acids joined together with a peptide bond in a condensation reaction

Question 4

Fibrous proteins

Answer 4

• Long, thin molecules
• insoluble in water
• parallel chains + many cross linkages = long fibres
• strong + stable
• eg. Keratin in hair

Question 5

Globular proteins

Answer 5

• Compact
• soluble in water
• e.g. Enzymes, antibodies, haemoglobin etc

Question 6

Test for proteins

Answer 6

1. Add a few drops of biuret solution
   2.it present-colour change of pale blue to lilac

Question 7

Primary structure of a protein

Answer 7

The sequence of amino acids in the polypeptide

Question 8

Secondary structure of a protein

Answer 8

1. Polypeptide chain coils into an alpha helix
2. Polypeptide chain folds into a beta pleated sheet

• hydrogen bonds

Question 9

Tertiary structure of a protein

Answer 9

Folding of the secondary structure into a specific 3D shape = functional properties

• disulphide, ionic, hydrogen bonds

Question 10

Quaternary structure of a protein

Answer 10

More than one polypeptide chain eg. Hb

Question 11

What are enzymes?

Answer 11

Globular proteins that act as biological catalysts

Question 12

Lock and Key Model

Answer 12

Substrate (key) is complimentary to the active site (lock) so they bind perfectly

Question 13

Induced fit model

Answer 13

The active site mould itself around the substrate and then becomes fully complementary = strain on the substrate and its bonds and lowers the energy needed to break the bonds

Question 14

Immobilised enzymes

Answer 14

Enzymes that have been trapped into an inert matrix which prevents them from moving

• Makes recovery and reuse of enzymes easier
• Ensures that the enzymes doesn’t contaminate the final product
• Allows for continuous processes
• Offers enzyme stability in temp. and pH = greater efficiency

Question 15

What are the factors affecting enzyme action?

Answer 15

1. Temperature
2. pH
3. Substrate concentration
4. Enzyme concentration

Question 16

Temperature on Enzyme Action

Answer 16

Higher temperature:
- increase in kinetic energy of enzyme + substrate molecules
- collide with enough energy more frequently
- increases rate of reaction

Question 17

Explain denaturation

Answer 17

When optimum temperature is reached, hydrogen bonds break → changes tertiary structure of enzyme → alters shape of active site → substrate will no longer fit the active site ( no longer complimentary)

Question 18

pH on Enzyme Action

Answer 18

• Increase / decrease = decrease in rate of enzyme activity
• H+ ions affect the hydrogen + ionic bonds in enzymes which hold the tertiary structure
  → change in shape of active site
  → enzyme is no longer complimentary to the substrate
  → no ES complexes form

Question 19

Define pH

Answer 19

Concentration of hydrogen ions present in a solution

pH = -log10 H+

Question 20

Substrate concentration on Enzyme Action

Answer 20

As more substrate is added, all active sites become occupied - rate is at maximum = enzyme saturated → line plateaus

Substrate conc is no longer a limiting factor

Question 21

Enzyme concentration on Enzyme Action

Answer 21

As the conc increases, there are more active sites available to form ES complexes = rate of reaction increases

All substrates become occupied = enzymes in excess - free ones with no substrate to bind to

Question 22

Competitive inhibitors

Answer 22

Similar shape to substrate so can bind to the active site→ presents the substrate from entering it = no ES complexes formed

Question 23

Non-competitive inhibitors

Answer 23

Attach themselves to the allosteric site → altering the shape of the active site → substrate = no longer complimentary → no ES complexes formed