control of enzyme activity

Question 1

kinetic explanation of enzymes

Answer 1

enzymes lower the delta G of the transition state (not the reaction!)
at really high concentration of substrate, enzyme will be saturated. even if substrate concentration is increased, there will still be a Vmax

Question 2

Vmax

Answer 2

• defined by a specific substrate concentration and cannot be increased by adding more substrate
• will increase by adding more enzyme

Question 3

Km

Answer 3

binding affinity
- adding more enzyme will increase the Vmax
- enzymes with higher ES affinity will reach 1/2 Vmax at a lower substrate concentration

Question 4

catalytic efficiency

Answer 4

= kcat (enzyme’s turnover number) / km

Question 5

positive cooperative binding

Answer 5

substrate binding increases protein affinity for subsequent substrates

Question 6

negative cooperative binding

Answer 6

substrate binding decreases protein affinity for subsequent substrates

Question 7

non-cooperative binding

Answer 7

substrate binding does not affect affinity for subsequent substrates

Question 8

T state

Answer 8

low affinity of hemoglobin for O2 (TOW RIGH)

Question 9

R state

Answer 9

high affinity of hemoglobin for O2 (TOW RIGH)

Question 10

competitive inhibition

Answer 10

inhibitor binds to the active site of the enzyme
Km (slope) increases (higher concentration of substrate is required to overcome effects of inhibitor)
Vmax (y-intercept) doesn’t change

Question 11

uncompetitive inhibition

Answer 11

inhibitor binds to allosteric site of enzyme substrate complex (affinity of substrate to enzyme increases but enzymatic activity decreases)
Km (slope) decreases
Vmax (y-intercept) decreases

Question 12

non-competitive inhibition

Answer 12

inhibitor binds to allosteric site of enzyme and decreases catalytic activity of active site regardless of whether substrate is already bound
Km (slope) is unchanged
Vmax (y-intercept) decreases

Question 13

mixed inhibition

Answer 13

inhibitor binds to allosteric site of enzyme, tends to have preference to binding to ES or E
Km increases if E binding preferred, decreases if ES binding preferred
Vmax decreases

Question 14

Allosteric enzymes

Answer 14

allosteric site present for molecules to bind and either upregulate or downregulate the enzyme function

Question 15

methylation

Answer 15

modification of a protein, DNA, or other molecule by addition of a methyl group (CH3)
methylation of DNA decreases gene expression

Question 16

acetylation

Answer 16

modification of a protein, DNA, or other molecule group by addition of an acetyl group (H3CC(O)OH)
(electron withdrawing acetyl group loosens DNA / histone interaction)
acetylation of DNA increases gene expression

Question 17

glycosylation

Answer 17

addition of a sugar to a protein, lipid, or other molecule

Question 18

suicide inhibition

Answer 18

suicide inhibitors covalently bind to enzymes and prevent them from catalyzing reactions

Question 19

zymogens

Answer 19

inactive form of an enzyme that requires covalent modification to become active
ex: digestive enzyme of pancrease trypsinogen