PL 2 - Kinetics

Question 1

What does a rate vs. substrate concentration graph look like for an enzyme-catalysed reaction?

Answer 1

Curved concave graph, positive gradient slowly decreasing

Question 2

What is the order with respect to the substrate at low and high concentrations?

Answer 2

Low concentrations: The order with respect to the substrate is 1
High concentrations: The order with respect to the substrate is 0

Question 3

Why are enzymes specific?

Answer 3

• Enzymes are proteins with tertiary level structure and hence have a specific 3D shape
• Enzymes have an active site which is highly specific and binds to complementary substrate only (forming an enzyme-substrate complex), allowing the reaction to occur

Question 4

How is enzyme activity affected by temperature?

Answer 4

• As temperature increases, enzymes and substrate have more kinetic energy
• Therefore there are more frequent and successful collisions, forming more enzyme-substrate complexes
• Rate of reaction increases

Question 5

What happens to the enzyme if temperature is too high?

Answer 5

• The enzyme becomes denatured
• Some hydrogen bonds and other tertiary structure bonds are broken/altered
• Hence the tertiary structure of the enzyme is different, along with the shape of its active site
• Active site is no longer complementary to the substrate; it cannot bind to form enzyme-substrate complexes
• Rate of reaction decreases

Question 6

Why are enzymes sensitive to pH?

Answer 6

• All enzymes have an optimum pH
• Anything outside this range will result in a lower enzyme activity
• A wildly different pH may alter tertiary structure bonds etc. and denature the enzyme, decreasing rate of reaction

Question 7

What is competitive inhibition?

Answer 7

• A competitive inhibitor has a similar shape/structure to the substrate
• It competes with the substrate for the active site of the enzyme, preventing it from binding
• This lowers the number of enzyme-substrate complexes formed, decreasing rate of reaction