Session 3 - Enzymes

Question 1

Explain the effects of enzymes on chemical reactions

Answer 1

Catalyse reactions
Increase reaction rate
Don’t alter equilibrium
Accelerate attainment of equilibrium
Reduce the activation energy of reaction

Question 2

What is the difference between an active site in a cleft and a crevice?

Answer 2

Active sites found in clefts are those between subunits and crevices are those between folds

Question 3

Define the standard rate of enzyme activity

Answer 3

1 unit = the amount of enzyme that produces 1 micro mole of product per min under standard conditions.

Question 4

Define Vmax, Km and V0

Answer 4

Vmax = maximum theoretical rate of enzyme activity. All enzymes are saturated by substrate
Km = the substrate concentration where the reaction velocity is half of Vmax
V0 = Initial rate of reaction

Question 5

What features in a line weaver burn plot indicate Km, Vmax and what does the gradient represent?

Answer 5

Km - x intercept = -1/Km

Vmax - y intercept = 1/Vmax

Gradient = Km/Vmax

Question 6

What effect do competitive inhibitors have on Km and Vmax and how is this seen on a line weaver burk plot?

Answer 6

Km increases, Vmax is unaffected (the substrate can out compete the inhibitor).
The y intercept is the same but the gradient is steeper

Question 7

What effect do non-competitive inhibitors have on Km and Vmax and how is this seen on a line weaver burk plot?

Answer 7

Km unaffected; Vmax decreases

On the graph this is seen by the x intercept staying the same and the gradient getting steeper