L5: Enzymes

Question 1

Why are enzymes needed?

Answer 1

1. High energy barrier of metabolic reactions
2. Fixed pH
3. Constant body temperature
4. Low concentration of metabolite
5. Metabolic regulation

Question 2

General features of enzyme

Answer 2

1. Catalytic site
2. Co-enzyme/Co-factor binding site
3. Regulatory site

Question 3

Characteristics of enzyme

Answer 3

1. Specific
2. Sensitive to pH and temperature (initially laws of chemical kinetics, later loss of functional structure)
3. Often require Co-enzyme (organic) / co-factors (inorganic) / prosthetic group (bind very tightly)

Question 4

Monomeric enzyme vs Oligomeric enzyme

Answer 4

Monomeric: Hyperbolic shape curve (level off) as all enzymes have been saturated (rate = SVmax/(k+S))

Oligomeric: Sigmoidal shape curve (positive cooperativity)

Question 5

Mechanisms of lower activation energy

Answer 5

1. Proximity and orientation
2. Electrostatic, acid-base, covalent interaction
3. Charge shielding by ions

Question 6

Mechanisms of action of enzyme

Answer 6

1. Lock and key hypothesis

2. Mechanical strain model (enzyme complementary to transition state —> lower activation energy)

Question 7

Ways of changing enzyme activity

Answer 7

1. Phosphorylation (kinase: add phosphate, phosphatase: remove phosphate)
   - fast
   - reversible
   - alteration of kinetic parameters
2. Allosteric regulator (+: shift curve to left / -ve: shift curve to right)
   - alter activity of catalytic site
3. Synthesis and breakdown of enzyme protein
   - slow
   - irreversible
   - long term regulation
   - alteration in enzyme abundance
4. Proteolysis
   - fast
   - irreversible
5. Activators/ inhibitors

Question 8

Why enzyme used in diagnostic procedure

Answer 8

1. Catalytic function e.g. thrombotic tendency

2. Specific location e.g. liver enzymes

Question 9

Enzymes as therapeutic targets

Answer 9

Drugs designed to inhibit enzyme

E.g. prostaglandin, angiotensin, cholesterol, bacterial cell wall