Enzymes and Bioenergetics

Question 1

What’s important to keep in mind about bioenergetics?

Answer 1

Delta G and Keq (energy of system)

Question 2

What’s important to keep in mind about kinetics?

Answer 2

Vmax and Km (speed of rxn system)

Question 3

Gibbs Free Energy Equation

Answer 3

∆G = ∆G0’ + RT ln (conc.products)/(conc. substrates)

Where
∆G0’ :change in free energy under standard conditions
R: the gas constant, 1.99 cal/molK or 8.31 J/molK
T: temperature, Kelvin
ln: natural log

Question 4

What does the net delta G represent?

Answer 4

Net delta G is the difference in chemical bond energy between the substrates and the products .

Question 5

If delta G is negative, what happens?

Answer 5

If ∆G is negative, the reaction will proceed spontaneously in the forward direction. Energy is released.

Question 6

If delta G is positive, what happens?

Answer 6

If ∆G is positive, the reaction will proceed spontaneously in the reverse direction.

Question 7

Define delta G naught.

Answer 7

Free energy change when starting with equimolar substrates and products.

Question 8

Define delta G naught prime.

Answer 8

Free energy change when starting with equimolar substrates and products at 25° C and pH 7.0.

Question 9

Define equilibrium constant Keq.

Answer 9

Describes how likely a reaction is to go forward/produce substrate.

Question 10

What is the principle behind the Gibbs free energy equation?

Answer 10

Unfavorable energetics can be overcome by manipulating the concentration of products and the concentration of substrates.

Question 11

What is the key difference between reactions in the lab and reactions in the body?

Answer 11

Reactions in the body have enzymes that act as catalysts.

Question 12

Define transition complex.

Answer 12

Max amount of tension in chemical system=peak in activation energy. Just as likely to go forward as it is reverse.

Question 13

How do enzymes speed up reactions?

Answer 13

1. Provide proximity and orientation of reactants
2. Ensure specificity of substrates and products
3. Stabilize the transition complex

Question 14

What is an additional way that enzymes can overcome unfavorable energetics?

Answer 14

Link reactions together.

Ex. Hexokinase LINKS phosphorylation of glucose to hydrolysis of ATP .

Question 15

In Michaelis-Menten equation, what are the constants?

Answer 15

Vmax and Km (units molar) ; these constants stay with the specific enzyme .

Question 16

What is the asymptote represent on the Michaelis-Menten curve?

Answer 16

Vmax

Question 17

What is the relationship between Km and activity of enzyme?

Answer 17

The lower the Km, the more active the enzyme.

Question 18

What do allosteric activators or inhibitors do to the Michaelis-Menten curve?

Answer 18

Changes curve from sigmoidal to hyperbolic curve.

Question 19

On a Lineweaver-Burke plot, what happens when -1/Km shifts to the right? To the left?

Answer 19

To right, Km getting bigger, enzyme activity less.

To left, Km getting smaller, enzyme activity more.

Question 20

What role does Pyruvate Kinase M2 (PKM2) play in cancer?

Answer 20

Chokes off glycolysis. Allows glycolytic intermediates to be diverted to biosynthetic pathways that provide building blocks for cell proliferation.

Question 21

What do competitive inhibitors do to the Km and Vmax?

Answer 21

Competitive inhibitors increase Km and don’t change Vmax.

Question 22

What do noncompetitive inhibitors do to the Km and Vmax?

Answer 22

Noncompetitive inhibitors decrease Vmax but don’t change Km.

Question 23

What do allosteric inhibitors do to the Michaelis Menten plot? What about Km and Vmax?

Answer 23

Allosteric inhibitors change the Michaelis Menten plot from hyperbolic to sigmoidal. Both Km and Vmax may be changed.