W10 Enzyme kinetics

Question 1

What does a catalyst do?

Answer 1

Provides an alternative pathway for the reaction in which the rate-determining step has a lower Gibbs activation energy.

Question 2

What is the difference between Non-catalysed reaction and catalysed reaction?

Answer 2

Non-catalysed reaction proceeds through a single transition state, whereas the mechanism for the catalysed reaction involves the formation of an intermediate

Question 3

What is the lock and key model?

Answer 3

Enzyme and Substrate are perfectly complementary
(+/- regions must match up in this model)
Free enzyme and Free substrate bind
Substrate binds REVERSIBLY
Reaction takes place
ESC forms
Products leave

Question 4

Examples of non-covalent interactions

Answer 4

Ionic bonds
Hydrogen bonds
Van der Waals forces

Question 5

What are the two distinct steps in an enzyme catalysed reaction?

Answer 5

1. reversible (substrate binding)
2. irreversible (formation of product)

Question 6

What happens in the Michaelis Menten Model? (3)

Answer 6

1. The enzyme binds a single substrate
2. Two distinct steps. The substrate binds reversibly but product formation is irreversible (always remember the reaction arrows…)
3. A steady state approximation applies: a method used to estimate the overall reaction rate of a multi-step reaction. It assumes that the rate of change of
   intermediate concentration (ES) in a multi-step reaction are constant.
   Can only be applied when the first step of the reaction is significantly slower than subsequent step in an intermediate-forming consecutive reaction

Question 7

What is the Steady State Approximation?

Answer 7

• Occurs very soon after start of reaction
  -Means the [ES] remains constant.
  -Rate of formation of ES = Rate of consumption of ES (conversion to E + P)

Question 8

According to the Steady State approximation..?
- The total concentration of the Enzyme increases over the time
- The concentration of the Enzyme-substrate complex and the concentration of the free enzyme remain steady over most of the reaction time
- The total concentration of the Enzyme decreases over the time
- At the initial phase of the reaction the concentration of the free enzyme increases

Answer 8

= B

Question 9

According to the lock and key model the shape of the active site only becomes complementary after the substrate has bound. True or false?

Answer 9

False

Question 10

What is the turnover number?

Answer 10

The number of substrate molecules converted into product by an enzyme molecule in a unit time when the enzyme is fully saturated with substrate.

The higher the number, the higher the efficiency

Question 11

At Vmax:
-The rate of reaction remains constant at the maximum value
-The reaction is of first order with respect to substrate concentration
-The enzyme active site is not saturated and available to bind fresh substrate
-The enzyme can increase its rate of reaction if more substrate is given

Answer 11

The rate of reaction remains constant at the maximum value

Question 12

What is KM equal to?

Answer 12

Substrate concentration at which the reaction velocity is half of V maximum (Vmax/2).

Question 13

What does a low KM mean?

Answer 13

Low KM means higher affinity for the enzyme, so a small amount of substrate is required to reach Vmax/2