Session 3 ILOs - Enzymes

Question 1

State the key features of enzymes

Answer 1

Enzymes are catalysts which increase the rate of reaction
They do NOT alter the equilibrium of a chemical reaction - they simply increase the rate at which the equilibrium is reached
Work by lowering the activation energy for a reaction

Question 2

Explain the role of the active site of an enzyme

Answer 2

The active site allows a substrate to bind to the specific region of an enzyme & forms the enzyme-substrate complex.
The active site is formed by amino acids from different parts of the primary sequence and reaction between the enzyme and the substrate is stabilised by surrounding amino acids within the active site
Substrates are bound to enzymes by weak bonds therefore allows the products to be released

Question 3

Describe how reaction rates vary as a function of enzyme concentration (assuming substrate concentration stays the same)

Answer 3

Rate of an enzyme-catalysed reaction is proportional to the enzyme concentration i.e. if you double conc. of enzyme, the rate of reaction doubles

Question 4

Describe how reaction rates vary as a function of substrate concentration (assuming enzyme concentration stays the same)

Answer 4

Rate of an enzyme-catalysed reaction increases as the substrate concentration increases, however this does plateau as the enzymes become saturated

Question 5

Define the 2 terms of activity & international unit of enzyme activity

Answer 5

Vmax and Vo are rates of activity

1 unit = the amount of enzyme that produces 1umol of product per min under standard condition

Question 6

Define Vmax & Km

Answer 6

Vmax = theoretical maximum rate of reaction when all of the enzyme molecules are saturated with substrate and they are proceeding as quickly as they can
Km = substrate concentration that gives half the maximal rate of reaction (Vmax)

Question 7

Describe the effects of the 2 types enzyme inhibitors on their kinetics and be able to between the two from simple graphs

Answer 7

Competitive inhibitor (binds at active site) & non-competitive inhibitor (binds at site away from the active site)

1. Competitive inhibitors
   Km increases, Vmax unaffected
2. Non-competitive inhibitors
   Km unaffected, Vmax decreases