Regulation And Inhibition Of Enzymes

Question 1

Free energy of activation

Answer 1

. Energy difference between reactants and TS

Question 2

Rate of reaction determined by___

Answer 2

. Molecules that have sufficient energy to overcome TS barrier
. Rate determined by # substrate converted to product per unit time

Question 3

T/F pH and temp do not affect enzyme activity

Answer 3

F

Question 4

Vo in Michealis Menten

Answer 4

Initial velocity

Question 5

Vmax in Michael is menten

Answer 5

. Max velocity

Question 6

Km in Michealis Menten

Answer 6

Michealis constant 
(K-1 + K2)/K1
. Equivalent to 1//2 Vmax on graph 
. Represent enzyme affinity to substrate 
. Small Km: high affinity
. Opposit for large Km

Question 7

Lineweaver-Burke Plot

Answer 7

. Double reciprocal plot
. I/[S] vs 1/Vo
. Intercept on x-axis: -1/Km
. Intercept on y axis: 1/Vmax

Question 8

Competitive inhibition

Answer 8

. Binds to same site as substrate on enzyme
. Overcome by inc. substrate
. Unaffected Vmax
. Km increased because it takes more substrate to achieve Vmax (X intercept closer to Y intercept in lineweaver Burke)

Question 9

Examples of competitive inhibitors

Answer 9

. Malonate for succinate

. Anti-hyperlipidemic agents inhibit HMG coreductase that catalyze 1st step in cholesterol

Question 10

Noncompetitive inhibition

Answer 10

. Inhibitor and substrate bind to different sites of enzyme
. Binding usually irreversible
. Vmax decreased because adding more substrate won’t overcome inhibition (Y intercept farther away from X axis)
. Km unaffected because inhibitor doesn’t bind to substrate binding site

Question 11

Example of noncompetitive inhibitor

Answer 11

. Lead

Question 12

Allosteric enzymes

Answer 12

. Regulated by effectors that bind noncovalently at site other than active site
. Contain multiple subunits
. Usually catalyze rate-determining steps in pathways

Question 13

Negative vs positive effectors

Answer 13

. Negative: inhibit enzyme activity
. Positive: inc. enzyme activity
. Can both effect Vmax, km, or both

Question 14

Homotropic effectors

Answer 14

. Substrate itself serves as effector
. Usually positive
. Presence of 1 substrate molecule at one site of enzyme (allosteric) enhances catalytic properties at catalytic site

Question 15

Do allosteric enzymes follow Michealis Menten kinetics?

Answer 15

NO, sigmoidal curve not hyperbolic

Question 16

. Heterotropic effector

Answer 16

. Effector different than substrate

. Feedback inhibition

Question 17

Kinases

Answer 17

. Phosphorylate things utilizing ATP as phosphate as donor

Question 18

Phosphatase

Answer 18

. Cleave phosphate groups from phorphylated enzymes

Question 19

Does phosphorylation of glycogen phosphorylase increase or decrease activity?

Answer 19

Increase

Question 20

Does phosphorylation of glycogen synthase increase or decrease activity?

Answer 20

Decrease

Question 21

What kind of enzymes are usually regulated by it’s rate of synthesis?

Answer 21

. Those needed at one stage of development or under selective physiological conditions