Intro to enzymes

Question 1

What is an enzyme?

Answer 1

Biological catalysts - compounds that increase the rate of a reaction. Enzymes are not consumed in the reactions they catalyze.

Question 2

What effect do enzymes have on equilibrium?

Answer 2

None - they do not alter equilibrium positions.

Question 3

What does the term saturation kinetics mean?

Answer 3

It refers to the fact that at a certain [S], the rate of the reaction will no longer increase. Thus, enzymes increase reaction rates but only to a point. When the amount of enzyme present becomes saturated with substrate, they can’t work any faster so the reaction rate levels off.

Question 4

Eqn for change in Gibbs free energy

Answer 4

ΔG = ΔH - TΔS

Question 5

What is the activation energy?

Answer 5

The energetic barrier between reactants and products, change in energy between reactants and transition state.

Question 6

What is Keq?

Answer 6

[Products] / [Reactants]

Question 7

What is the transition state?

Answer 7

Hypothetical state between substrate conformation and product conformation, in uncatalyzed rxn ligand could slide back down to substrate form or proceed forward to product form

Question 8

What is enzyme binding energy?

Answer 8

Binding energy is the energy that is released when the enzyme interacts with and binds to the substrate

Question 9

What role does binding energy play in lowering activation energy?

Answer 9

Binding occurs through VDW, H-bonds, and ionic interactions. The energy that is released from these interactions is used to alter the shape of the substrate to achieve its transition state. As such, the energy of the transition state (activation energy) of the substrate is lowered. The shape of the active site of the enzyme is complementary to the structure of the transition state of the substrate so that the structure of the transition state is stabilized, and thus lower in energy, than if the enzyme were not present.

Question 10

Why is Vo measured early in the reaction?

Answer 10

Because [S] hasn’t changed substantially

Question 11

Line-weaver Burke Plot:
A) What is the slope?
B) What are the units of the x-axis?
C) What is the x-intercept?
D) What are the units of y-axis?
E) What is the y-intercept?

Answer 11

A) Km / Vmax
B) 1 / [S]
C) -1 / Km
D) 1 / V
E) 1 / Vmax

Question 12

How does competitive inhibition alter the Km? Vmax? Lineweaver burke plot?

Answer 12

Km is higher (lower affinity)
Vmax is unchanged
X-intercept is closer to 0