Lecture 15 - Enzymes

Question 1

How do enzymes work?

Answer 1

Provide alternate pathway for reaction to occur by lowering the ΔG (Energy of activation) for the transition state. Forms multiple weak interactions with substrate, releasing energy which is used to lower the activation energy.
Do not affect equilibrium point, just the rate of reaction
Can bind to 2 substrate and help with orientation, create charge on substrate, or create strain on substrate to force it to transition state

Question 2

What are the 2 models of enzyme binding

Answer 2

Lock and key –> substrate and enzyme fit perfectly. why would it go to transition state/products, needs large energy to do that, how do products fit in active site?
Induced fit –> substrate and enzyme not perfect fit, but close, creates strain to force substrate to transition state which optimizes binding and weak interactions, both undergo conformational change, keeps TS under strain to force it to either products or back to reactants

Question 3

What are cofactors and coenzymes?

Answer 3

Cofactors are metal ions, coenzymes are organic compounds not synthesized by body. Can stabilize transition state, help orient substrate. Can be either prosthetic or transient

Question 4

What is the Michaelis-Menten equation?

Answer 4

Vo=Vmax [S]/([S}+Km)

Levels off at high [S] because all of the active sites on an enzyme are saturated

Question 5

What does Km indicate?

Answer 5

Affinity for substrate, high Km=low affinity

Question 6

What is Kcat?

Answer 6

substrate converted to products when enzyme fully saturated, indication of speed fo reaction

Question 7

How do you measure efficiency?

Answer 7

Kcat/Km, high affinity, high turnover
Some enzymes approach diffusion rate, can only process substrates at rate encountered in solution (every collision productive)

Question 8

What are allosteric enzymes?

Answer 8

have multiple active sites, binding to one site can influence binding at another site (cooperative binding) can be negative or positive

Question 9

What are the two types of inhibition

Answer 9

Competitive –> inhibitor resembling substrate binds to active site, directly competes for active site. Can fix by increasing substrate concentration
Non-competitive –> inhibitor binds to allosteric site, has negative allosteric effect on substrate binding, influences active site conformation

Question 10

What are irreversible inhibitors?

Answer 10

bind to enzyme and inactivate, usually toxic