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MFM > Enzymes > Flashcards

Enzymes Flashcards

1
Q

what is the lock and key hypothesis

A

substrate fits into a substrate binding site to form a reaction intermediate

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2
Q

what is the induced fit hypothesis

A

enzyme molecule changes shape as the substrate molecule gets close, the change in shape is induced by the substrate binding molecule

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3
Q

what is the significance of the active site

A

substrate binding site usually close to or equal to active site, the proximity, orientation and chemical environment inside active site as well as helping groups (cofactors/coenzymes) allows chemical reaction to proceed more easily

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4
Q

what occurs if mutation or inhibitor affects substrate binding site?

A

enzyme has altered affinity for its substrate (increases Km)

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5
Q

what occurs if mutation or inhibitor affects active site?

A

enzyme will have altered activity (decreased Vmax)

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6
Q

what are the cofactors?

A

metal ions Fe2+, Mg2+, and Zn2+ ,contribute to catalytic process by acting as electrophiles, assist in the binding of the substrate

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7
Q

what are coenzymes

A

non-protein organic molecules like vitamins

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8
Q

what is a transition state?

A

ES in which the bonds are undergoing transformations that are UNLIKE starting material NOR product, usually in a strained or distorted formation, so the energy is increased from the initial state

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9
Q

what does an enzyme do in relation to ES?

A

enzyme binds to its substrate and reduces the activation energy of the reaction by stabilizing the transition state making the substrate more likely to react and speeds up the reaction

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10
Q

what affects the rate of enzyme catalyzed reactions?

A
  1. concentration of enzyme and substrate
  2. pH
  3. temp
  4. activators and inhibitors
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11
Q

what is the relationship between substrate and reaction velocity in a NON-enzymatic reaction?

A

linear, velocity is proportional to substrate concentration

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12
Q

what occurs when an enzyme catalyzed reaction is at a very high substrate concentration?

A

velocity increases until Vmax, where enzyme is saturated, and the velocity of the reaction is zero order - constant and independent of S concentration

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13
Q

what occurs when an enzyme catalyzed reaction is at a very low substrate concentration?

A

the reaction is first order, the velocity is proportional to the concentation of substrate, and velocity increases with respect to substrate concentration

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14
Q

what is drug elimination kinetics?

A

the metabolism of a drug to inactive metabolites usually by the liver in a first order or zero order elimination kinetic method

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15
Q

how are drugs usually excreted?

A

kidney, bile duct, lungs, sweat

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16
Q

what is the first order drug elimination kinetic?

A

a constant FRACTION of drug is eliminated with time, is an exponential decay plot, ie 1/2 is gone in 1 hour, 1/4 in 2 hour, 1/8 in 3 hours, when drug concentration is high, rate of disappearance is also high, the elimination mechanisms are not saturated, a fixed half life

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17
Q

what is the zero order drug elimination kinetic?

A

constant amount of drug eliminated with time, ie 10mg per hour, no fixed half life, the elimination mechanisms can be saturated

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18
Q

what occurs if high doses of drugs or hepatic/renal diseases impair drug elimination?

A

elimination process becomes saturated and zero order,

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19
Q

what occurs at extreme pH

A

proteins are denatured, and active site is distorted and substrate molecules no longer fit in it

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20
Q

what occurs at a slightly different pH than optimal?

A

alters interaction between E and S, so reaction proceeds at slower rate

21
Q

what occurs at extreme temperatures?

A

high and low temps, enzymes denatured and reaction velocity is decreased

22
Q

what is the michaelis-menten model?

A

enzyme and substrate combine at the rate of complex formation (k1) to produce ES, then ES proceeds at the rate of product formation (k2) to produce the product E+P

23
Q

3 assumptions of MM model

A
  1. there is a formation of an ES complex
  2. the concentration of substrate is much greater than [enzyme]
  3. ES does not change with time (the steady state assumption, initially has a burst and then its concentration will not change demonstrably), and the rate of formation of ES is equal to the rate of breakdown of ES
24
Q

what is the MM equation?

A

velocity of product formation= rate of formation of product (k2) x concentration of ES

is equal to velocity = vmax x ([S])/Km + [S]

25
Q

what is Km

A

the substrate concentration at half of the max velocity, aka the affinity of the enzyme to substrate, a lower Km indicates a higher affinity, a higher Km indicates a lower affinity

26
Q

what best describes the MM graph?

A

it is a combination of zero and 1st order kinetics, where when the S is low, it is 1st order, but when S is high, it is 0 order, aka a hyperbolic curve

27
Q

what is Kcat?

A

k2, turnover number, max number of substrate molecules converted to product per enzyme molecule per unit time, =Vmax/enzyme molecule #, units are time^-1

28
Q

what does a lower Km indicate?

A

higher affinity and tighter binding, achieves Vmax at low [S]

29
Q

what does a higher Km indicate?

A

a lower affinity and weak binding, achieves Vmax at high [S] (takes higher S to achieve Vmax)

30
Q

what is vmax?

A

theoretical max velocity of reaction at the saturating substrate concentration

31
Q

what is the lineweaver-burk double reciprocal plot?

A

the double reciprocal of MM graph where Km and Vmax can be determined easier

32
Q

where is Km on a lineweaver Burk plot?

A

hits X axis, is -1/Km

33
Q

where is Vmax on lineweaver Burk plot

A

hits y axis, is 1/vmax

34
Q

types of enzyme inhibitors

A

both decrease rate of enzymatic reactions

  1. irreversible - also called suicide inhibitor or mechanism based inhibitor
  2. reversible
35
Q

what do irreversible enzyme inhibitors do?

A

inhibitor irreversibly inactivates enzyme by destroying or covalently modifying key AA residues - the enzyme CANNOT function anymore, and inhibition cannot be stopped, decreases substrate binding and decreases RR

36
Q

how does penicillin act as an enzyme inhibitor?

A

it irreversibly inhibits glycopeptidyl transferase which is required for bacterial cell wall synthesis

37
Q

how does aspirin act?

A

irreversibly inactivates COX1 and COX2

38
Q

what does lead do to the body?

A

irreversibly inhibits ALA dehydratase and ferrochelatase (needed for heme biosynthesis)

39
Q

what do organophosphate compounds do to the body?

A

malathion, parathion, nerve gas sarin, DFP irreversibly inactivate acetylcholinesterase by forming covalent complex with active site serine in Ach-ase

40
Q

MOA of allopurinol

A

binds irreversibly to active site of xanthine oxidase, which then converts allopurinol into its active metabolite, oxypurinol, which binds tightly to the active site and is only slowly released

41
Q

what does xanthine oxidase do?

A

converts hypoxanthine to xanthine and then to uric acid

42
Q

2 types of reversible inhibitors

A
  1. competitive

2. non competitive

43
Q

what is a competitive inhibitor?

A

inhibitor resembles substrate but cannot undergo catalytic step, competes with substrate for binding, SO IT CHANGES THE KM (USUALLY INCREASE), BUT VMAX STAYS THE SAME

44
Q

example of competitive inhibitor

A

statin drugs - competitively inhibit rate limiting step in cholesterol synthesis
ex. HMG CoA reductase inhibitor is lipitor, structural analog of HMG CoA

45
Q

example of competitive inhibitor

A

methotrexate, structural analog of folic acid and inhibits dihydrofolate reductase and stops thymidine biosynthesis, inhibits DNA replication and mitosis in rapidly growing cells - an antimetabolite

46
Q

what is a non-competitive inhibitor?

A

a molecule or ion that binds on a site on th eenzyme so that it affects Vmax - not on substrate binding site, enzyme can bind both substrate and inhibitor, but cannot make a product, decreases kcat and Vmax, no effect on Km

47
Q

example of non-competitive inhibitor

A

physostimine, for MG, binds reversibly to Ach-ase away from active site, Km remains the same bc normal binding not affected, but reduces catalytic activity of enzyme, reducing Vmax

48
Q

example of non-competitive inhibitor

A

captopril, for HTN, reversible noncompetitive inhibitor of ACE (angiotensin-converting enzyme)

49
Q

ACE inhibitor mechanism

A

renin in kidney converts angiotensinogen to angiotensin I, then proteolytically cleaved to make angiotensin II by ACE, angiotensin II increases renal fluid/electrolyte retention

MFM (39 decks)

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