Lecture 11

Question 1

What is a progress curve?

Answer 1

Measures the appearance of product( or disappearance of substrate) with time at steady state.

Question 2

What are the symbols for Initial velocity?

Answer 2

V0, V1, Vinit

slope of line at beginning

Question 3

What is the effect of enzyme concentration on reaction rate?

Answer 3

If there is sufficient excess of substrate, then as the amount of enzyme is increased, the rate of reaction increases.
(Initial velocity is proportional to enzyme concentration when substrate is in excess.)

Question 4

What is the effect of substrate concentration on reaction rate?

Answer 4

• There is usually a fixed amount of enzyme and varying amount of substrate.
• As substrate concentration is increased, the initial rate increases in a linear way at first, but aas all enzyme active sites become occupied, the rate of reaction stops increasing

Question 5

What is maximum velocity?

Answer 5

At some point the reaction reaches a maximum speed regardless of how much substrate is available - this is called maximum velocity.

Question 6

What is catalysis?

Answer 6

The acceleration of a chemical reaction via a catalyst.

Question 7

What is the overall process?

Answer 7

Enzyme plus substrate exist separately in a solution, they bind together to form an enzyme substrate complex which then reacts at some rate to form enzyme plus product. (we want to find rate of complex - product)

Question 8

What is the Mechaelis-Menten equation?

Answer 8

Used to determine an enzymes kinetic parameters.
Velocity we observe at beginning is related to maximum velocity by the ratio of substrate concentration to Km value plus substrate concentration.

Question 9

What assumptions are made from the model reaction?

Answer 9

• Product is not converted back to substrate
• The rate of ES formation equals the rate of its breakdown
• Measuring initial rates insures (S) does not change significantly and (s) is much greater than (E).

Question 10

Time course of reaqtcion?

Answer 10

(ES) at any time will govern the rate.

“steady rate” refers to time during which (ES) does not change

Question 11

Assumptions made when Mechaelis-Mentin model fits?

Answer 11

• All ES complexes have same rate of reaction
• (S) is in vast excess to (E)
• Rate of ES formation = rate of it’s breakdown
• Initial rate is measured. That is early enough that (S) does not change significantly
• The reverse reaction does not occur

Question 12

What are allosteric enxymes?

Answer 12

Change shape and activity, and control metabolic pathways.

Question 13

Features of allosteric enzymes?

Answer 13

They often have multiple subunits and display cooperative behaviour.

Question 14

Why do cooperative enzymes not follow the Michaelis Menten equation?

Answer 14

• Sigmoidal curve not hyperbolic.
• responds more steeply to intermediate changes in (S)
• evolve at regulatory points in metabolic pathways
• Recall hemoglobin.

Question 15

Role of inhibitors and activators in regards to conformation?

Answer 15

Inhibitors stabilize the T form.

Activators stabilize the R form.