AL - Kinetics 3

Question 1

What is a Lineweaver-Burke plot used for?

Answer 1

Helps determine Vmax and Km values

Question 2

What are the axis for a Lineweaver-Burke plot?

Answer 2

Y-axis: 1/v

X-axis: 1/[S]

Question 3

How do you work out Vmax and Km values from a Lineweaver-Burke plot?

Answer 3

Y-intercept: 1/Vmax

X-intercept: -1/Km

Question 4

What are 2 problems of the Lineweaver-Burke plot?

Answer 4

• Data fitting is biased towards high 1/[S], low [S] data
• Data at low [S] are less reliable as signal changes are smaller.

Question 5

What is considered a better alternative to the Lineweaver-Burke plot?

Answer 5

The Hanes-Woolf plot

Question 6

What are irreversible inhibitors? (2)

Answer 6

• Covalently modify the enzyme
• Permanently inhibit the reaction until fresh protein is synthesised

e.g ASPIRIN (inhibits cyclooxygenase)

Question 7

What are reversible inhibitors? (2)

Answer 7

• Temporarily bind to the enzyme
• Activity is restored when the inhibitor is displaced or removed

Question 8

What are the 4 types of reversible inhibitors?

Answer 8

1. Competitive inhibitors- Compete with the substrate to occupy the active site
2. Uncompetitive inhibitors- Bind to the enzyme-substrate complex and prevent catalysis
3. Mixed inhibitors- Bind to both the free enzyme and ESC (with different affinities)
4. Non-competitive- Bind to enzyme-free and ESC equally well

Question 9

What is the Y-intercept, X-intercept and gradient of a Hanes-Woolf plot?

Answer 9

Y-intercept: Km/Vmax
X-intercept: -Km
Gradient: 1/Vmax

Question 10

How does a competitive inhibitor affect Km and Vmax values?

Answer 10

Km: Increases

Vmax: Stays the same

Question 11

How does an uncompetitive inhibitor affect Km and Vmax values?

Answer 11

Km: Decreases

Vmax: Decreases