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Flashcards in Enzyme Kinetics Deck (60):
1

In the Michaelis-Menten Kinetcs, the ___ is always rate limiting step

k2/kcat

2

Enzyme kinetics are important for:

1. Drug design
2. Drug interactions
3. Toxins (making anti-toxins)

3

In enzyme kinetcs catalyzed reactions, the stubstrate:

will be used up until equilibrium is attained

4

In the very beginning there is a very ____relationship

linear

5

As substrate comes ____, product goes ____

down; up

6

What is going on during pre-steady state

concentration of ES is building up

7

What is going on during the steady state

After pre steady state, concentration of ES and any other intermediates reaches point where concentrations are approx constant,

8

What is the steady state kinetics experiment like

1. Set up several reactions
2. [E] same in each
3. Different substrate conc.
4. Plot amount of P formed against time
5. Measure velocity

9

What does the michaelis menten equation describe

the curve obtained by plotting Vo, initial velocity against [S], the substrate concentration

10

What is Km

The michaelis menten constant which is the substrate concentration at which Vo= 1/2 Vmax

11

When substrate concentration is much less than Vmax, what kind of relationship do you get

linear= 1st order kinetics

12

When substrate concentration is much higher than Km:

The eqn reduces to Vo=Vmax; adding more substrate doesnt make a difference. This is called 0 order kinetics.

13

What is the lineweaver-burk equation

Transforms michaelis menten equation into equation that gives a straight line plot

14

What is the slope = to in a lineweaver burk plot

Km/Vmax

15

What does Km depend on

1. Substrate used
2. pH
3. Temperature

16

Hexokinase is the first enzyme in

glycolysis; phosphoralates glucose

17

What does Km mean

Can be used to calculate the fraction of active sites filled at any substrate concentration

18

Km is related to the rate constants of each step in the ____reaction

catalytic

19

WHat is Kd

the dissociation constant for the ES complex; provides a measure of the affinity of the enzyme for its substrate.

20

Another way to describe kcat is that it is the:

turnover constant=number of substrate molecules converted to product per unit time by a single enzyme molecule saturated with substrate.

21

What is catalytic efficiency = to

the factor kcat/km

22

What are two broad classes of enzyme inhibitors

1. Reversible
2. Irreversible

23

Aspirin inhibits which enzyme

cylooxygenase; which is used for inflammation/pain

24

ACE inhibits which enzyme

angiotensin converting enzyme; which then dec blood pressure

25

Statins inhibit which enzyme

HMGCoA reductase; lowers cholestrol

26

Simbrinza inhibis which enzyme

Carbonic anhydrase; glaucoma

27

What are the three types of reversible inhibitors

1. competitive
2. uncompetitive
3. mixed inhibition (non-competitive)

28

What is a competitive inhibitor

a compound that resembles a normal substrate; competes with substrate for binding to active site but no reaction occurs when bound.

29

What does a compettive inhibitor curve look like

Vmax doesnt change, just takes more substrate to get there. Km (increases) and slope changes.

30

What is DIFP

An irreversible inhibitor; it combines with reactive serine 195 and makes a covalent bond and just sits there. Doesnt come off

31

What are target enzymes for DIFP

1. Acetylcholinesterase
2. Chymotrypsin

32

What is penicillin

An irreversible inhibitor; once bound in active site, beta lactam ring covalently reacts with active site serine (enzyme activity irreversibly destroyed)

33

What are suicide inhibitors

Special class of irreversible inhibitor. Bind to active site and begin to participate in normal enzyme reactions. Form an intermediate that is covalently bound to an active site reactive group as a normal step in reaction. Do not undergo further steps

34

What is an ex of a suicide inhibitor

Flourouracil: impt chemotherapeutic agent in cancer treatment that targets production of DNA precursors.

35

What are the four major mechanisms of regulation of enzyme activity

1. Stimulation and inhibition by control proteins.
2. Reversible covalent modification
3. Proteolytic activation
4. Allosterism

36

Neutrophils are

the first cells that arrive and invade foreigners. Break down ECM in area.

37

What is alpha 1 antitrypsin

potent elastase inhibitor; binds strongly, blocks active site -- deficiency causes emphysema (CT in lung damaged)

38

What is elastase

released by neutrophils responding to bacterial infection; degrades collagen and elastin

39

What is reversible covalent modification

reversible attachment of small functional group. Often phosphoryl group. Alters activiy: enzymes in glycogen metabolism

40

WHat is proteolytic activation

Zymogen: inactive precursor of enzyme; irreversibly activated by proteolytic cleavage of one or more peptide bonds.

41

What are examples of proteolytic activation

blood clotting enzymes, digestive enzymes, angiotensin II

42

Kinases

phosphoralates things

43

What is allosterism

A change in the conformation and as a result activity - of an enzyme resulting from the binding of a compound at a site on the enzyme other than the active binding site.

44

What is a modulator (effector)

regulatory metabolite that modulates enzyme activity, usually by reversible, non covalent binding

45

Allosteric enzymes show ____rate curves

sigmoid (instead of hyperbolic)

46

Positive modulators ____substrate affinity

increase

47

Negative modulators (inhibitors)____substrate affinity

decrease

48

Sigmoidal substrate activity curves are consistent with subunits exhibiting

cooperativity (hemoglobin)

49

WHat is cooperativity

The influence of the binding of a ligand to one subunit on the binding of a ligand to a second subunit; usually involves conformational change

50

What are the two observations that the models for allosterism explain?

1. Sigmoidal curve with substrate alone (no modulators)
2. Change in curve in response to positive and negative modulators

51

What are the two models of allosterism

1. Concerted (symmetry) model
2. Sequential model

52

What does the concerted/symmetry model propose

an allosteric enzyme molecule can exist in only two states:
1. Tense state
2. Relaxed state

53

What is relaxed state

All subunits are in active or high affinity state

54

What is tense state

all subunits are in inactive or low affinity state

55

What is an activator:

Binds to R form, shifting equilibrium and increasing substrate binding

56

What is an inhibitor

Binds preferentially to T form, shifting equiliubrium, decerases substate binding

57

What is the sequential model

Binding of ligand to any one subunit causes a conformational change in that subunit; change partially transmitted to one or more adjacent subunits.

58

What is activator binding

causes conformational change to increase subunit affinity for substrate or can increase effect transmitted by subunit

59

What is inhibitor binding

Causes conformational change to decrease subunit affinity for substrate or can dec effect transmitted by subunit.

60

The best example of allosteric regulation is:

hemoglobin