Enzyme Kinetics and Inhibition 10/4

Question 1

characteristics of enzymes

Answer 1

1. cataylze chemical reactions without being consumed 2. very selective 3. products of natural selection

Question 2

delta G less than 0

Answer 2

spontaneous reaction

Question 3

delta G greater than 0

Answer 3

non-spontaneous reaction

Question 4

enzyme catalysis reaction

Answer 4

E+S →[ES]→E+P

Question 5

active site

Answer 5

has a shape that accomodates and complements the subtrate, including polarity and charge complentarily to the substrate transition state

Question 6

to be an effective catalyst, should the enzyme bind tighter to the substrate or to the transition state?

Answer 6

the transition state! **this makes TS analogs good inhibitors of enzyme (for drugs)

Question 7

kcat

Answer 7

the rate at which the ES complex converts to free enzyme and product. units: s^-1

Question 8

Km

Answer 8

the dissociation constant for the enzyme substrate complex. units=M

Question 9

Vmax

Answer 9

the maximal value for an enzyme reaction

Question 10

rate saturation equation

Answer 10

[E]₀=[E]+{ES]

Question 11

when [S] is low, the enzyme is mostly ________. how does v increase?

Answer 11

[E]

v increases proportionally to [S]

Question 12

when [S] is high, the enzyme is mostly _____. how does v increase?

Answer 12

[ES]

v increases slowly in proportion to [S]

Question 13

steady state enzyme kinetics equation

Answer 13

v=(Vmax[S])/Km+[S]

Question 14

the upper limit of the forward reaction is

Answer 14

Kcat

Question 15

carbonic anhydrase

Answer 15

catalyzes interconversion of carbon dioxide and bicarbonate

Question 16

reversible inhibitor I

Answer 16

binds and dissociates from an enzyme; doesn’t react, just prevents substrates from reacting

Question 17

irreversible inhibitor

Answer 17

binds to and permanently inactivates an enzyme

Question 18

how does aspirin affect COX (cyclooxygenase)?

Answer 18

aspirin inactivates cox enzymes (cox synthesize prostaglandins, causing inflammation) - aspirin PERMANENTLY acetylates the active site serine residue. this slows blood clotting

Question 19

aspirin toxicity

Answer 19

1. salicylate (the remainder of the aspirin molecule ones it inactivates COX) binds to other proteins causing tinnitus (ear ringing) - can result in SATURATION of liver enzymes
2. anion gap metabolic acidosis - interrupts aerobic respiration, leading to anaerobic production of lactate

Question 20

for reversible enzyme inhibitors, the amount of inhibition depends on:

Answer 20

the concentration of the inhibitor [I]

Question 21

competitive inhibitors prevent substrates from binding to…

Answer 21

the free enzyme. normally binds to the enzyme’s ACTIVE SITE

Question 22

noncompetitive inhibitor

Answer 22

has no effect on substarte binding - prevents reaction of the bound substrate

Question 23

dihydrofolate reductase (DHFR)

Answer 23

enzyme that is used to make DNA

Question 24

what does methotrexate inhibit?

Answer 24

DHFR - used in leukemia (acute lymphoblastic leukemia) treatments. is COMPETITIVE inhibitor

Question 25

there are 5 ways that enzymes can be regulated. they are:

Answer 25

1. substrate/cofactor availability
2. product inhibition
3. allosteric activation and inhibition
4. positive and negative cooperativity
5. post-translational modification

Question 26

negative feedback

Answer 26

the product inhibtis the process from happening again

Question 27

glucose-6-P is catalyzed by:

Answer 27

glucokinase and hexokinase

Question 28

the Km for glucose is higher in ______ than _______. why is this important?

Answer 28

Km is higher in glucokinase (10mM) than hexokinase (0.1 mM). This means that hexokinase has a high affinity for the substrate

Question 29

allosteric regulation of an enzyme occurs where? what type of inhibitors do this?

Answer 29

at a site on the enzyme OTHER that the active site. noncompetitive inhibitors are allosteric inhibitors.

Question 30

thrombin

Answer 30

a blood clotting factor. has 2 confirmations:

1. slow: an anticoagulent (cleaves protein C, a clotting inhibitor)
2. fast form: cleaves fibrinogen; coagulent

conversion between the slow and fast forms is ALLOSTERICALLY REGULATED by the binding of Na⁺

Question 31

amount of slow/fast thrombin in the blood?

Answer 31

serum thrombin is 60%fast/40%slow

Question 32

what type of curve does positive cooperativity give?

Answer 32

sigmoid curve - means that v is less responsive at low [S]

Question 33

glycogen phosphorylase

Answer 33

enzyme that converts glycogen to glucose-1-P. exists in 2 forms.

1. b (native form), T (tense) state - has a high Km, or poor substrate affinity (would want to DISSOCIATE)
2. a form favors R (relaxed) state, has low Km, meaning it has high substrate affinity

(a phosphorylase converts the a form back to the b form)

Question 34

AMP is a(n) ____________ activator

Answer 34

allosteric

Question 35

what is a zymogen?

Answer 35

an inactive precursor that is turned on by proteolytic cleavage, many pancreatic/digestive enzymes are this