Exam 3: Lecture 19

Question 0

Analysis of reaction rates

Answer 0

• A–>P
• Rate (V) = quantity of loos of A or gain of P over time
• Considering only loss of A: V=k[A] (units of M (molarity))

Question 1

What is enzyme kinetics?

Answer 1

• The study of biochemical reactions that are catalyzed by enzymes.
• Focused on reaction rates

Question 2

Second order reaction

Answer 2

• 2A–>P

* V = K[A]^2

Question 3

Steady-state Kinetics assumptions:

Answer 3

1. ES is in rapid equilibrium with E and S
2. Rate of ES formation = rate of ES breakdown, therefore ES is essentially constant
3. S»>E, therefore S is essentially constant
4. Initial velocity of reaction is measured from time = 0 (thus, V0)

Question 4

_____ is the substrate concentration that produces ______ for the catalyzed reaction

Answer 4

•Km, 1/2 Vmax

Question 5

Vo =

Answer 5

• Vmax [S]/[S] + Km

* Therefore, when S = Km, then Vo = Vmax/2

Question 6

Km

Answer 6

• Has units of molarity (M)
• Is independent of enzyme amount and purity
• Is dependent on assay conditions such as pH, presence of inhibitors or activators, temp, and ionic strength. This is b/c Km is constructed purely of rate constants.

Question 7

Vmax

Answer 7

• Has units of umol/min
• Is dependent on amount of enzyme used
• Is the highest reaction rate that can be attained b/c all of the enzyme is saturated with substrate

Question 8

Kcat

Answer 8

• Kcat = Vmax/[Etotal]
• either the catalytic constant or turnover number
• Tells how many molecules of substrate the enzyme can convert into product each second at saturating

Question 9

Lineweaver-Burk Plot

Answer 9

• 1/Vo = Km/Vmax [S] + 1/Vmax

* be able to find numbers off graph

Question 10

Why would an enzyme reaction need multiple substrates with different Km values to obtain the desired product?

Answer 10

•different affinity for the active sites

Question 11

Kcat/Km

Answer 11

• measure of catalytic efficiency

* maxes out at the simple diffusion rates

Question 12

Bisubtrate reactions

Answer 12

• most biochemical reactions start with 2 substrates and end with two products
• mostly transfer a functional group from one substrate to the other
• Sequential and Double-displacement (ping-pong) reactions

Question 13

Sequential Reactions

Answer 13

•All substrates bind to the enzyme before any product is released

Question 14

Double-displacement (ping-pong) reaction

Answer 14

• One of the products is released before a second substrate binds

Question 15

Enzyme Inhibition

Answer 15

• Interfere with catalysis by slowing or halting enzymatic reactions
• important pharmaceutical agents
• Competitive, Uncompetitive, and Noncompetitive inhibitors