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MCAT Biochemistry > Enzymes > Flashcards

Enzymes Flashcards

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MCAT flashcards
1
Q

Enzymes

A

incredibly important as biological catalysts

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2
Q

catalysts

A

do not impact the thermodynamics of a reaction; Hrxn and equilibrium position do not change but the reaction proceeds at a much faster rate

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3
Q

Key points about enzymes

A
  • lower the activation energy
  • increase rate of reaction
  • do not alter the equilibrium constant
  • are not changed or consumed in the reaction (appear in both reactants and products)
  • are pH and temperature sensitive
  • do not affect the overall ΔG of reaction
  • are specific for a particular reaction or class of reactions
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4
Q

enzyme specifity

A

enzymes will only catalyze a single reaction/class of reactions for a particular substrate

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5
Q

oxidoreductase

A

catalyze redox reactions; transfer electrons between biological molecules; often has a cofactor that acts as an electron carrier

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6
Q

reductant

A

electron donor

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7
Q

oxidant

A

electron acceptor

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8
Q

transferase

A

catalyze the movement of a functional group from one molecule to another

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9
Q

kinase

A

catalyze the transfer of a phosphate group to another molecule

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10
Q

hydrolase

A

catalyze the breaking of a compound into two molecules by addition of water

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11
Q

lyase

A

catalyze the cleavage of one molecule into two products; do not require water and do not act as oxidoreductases

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12
Q

synthase

A

synthesis of two molecules into one molecule

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13
Q

isomerase

A

catalyze the rearrangement of bonds within a molecule; catalyze reactions between stereoisomers as well as constitutional isomers

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14
Q

ligases

A

catalyze addition or synthesis reactions, generally between large similar molecules and often require ATP; nucleic acid synthesis/repair

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15
Q

lyase

A

catalyze addition or synthesis reactions, generally between small similar molecules and often require ATP

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16
Q

endergonic reaction

A

require energy input (ΔG>0)

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17
Q

exergonic reaction

A

energy is given out (ΔG<0)

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18
Q

activation energy

A

catalysts lower the activation energy to make it easier for the substrate to reach its transition state

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19
Q

enzyme-substrate complex

A

physical interaction between substrate and enzyme

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20
Q

active site

A

the location within the enzyme where the substrate is held during chemical reaction

21
Q

lock and key theory

A

proposes that the enzymes active site is already in the appropriate conformation for the substrate to bind

22
Q

induced fit model

A

the substrate induces a change in the shape of the enzyme; the enzyme returns to its original state after the interaction

23
Q

cofactors/coenzymes

A

bind to the active site of the enzyme and participate in the catalysis of a reaction

24
Q

apoenzymes v. holoenzymes

A

apoenzymes: enzyme without its cofactors
holoenzymes: enzyme with its cofactors

25
Q

prosthetic groups

A

tightly bound cofactors/coenzymes necessary for enzyme function

26
Q

cofactors

A

generally inorganic molecules or metal ions; often digested as dietary minerals

27
Q

coenzymes

A

small organic groups, the vast majority of which are vitamins or derivates of vitamins such as NAD+, FAD or coenzyme A

28
Q

water-soluble vitamins

A

B complex and vitamin C (Ascorbic acid)

29
Q

fat-soluble vitamins

A

A,D,E,K

30
Q

saturation

A

at this rate, enzyme is working at maximum velocity (Vmax)

31
Q

Michaelis-Menten

A

E+S()ES->E+P

where is k(1) and the second -> is Kcat

32
Q

Michaelis-Menten

A

v=(Vmax[S])/(Km+[S]) or v=(Kcat[E][S])/(Km+[S])

Km=substrate concentration at which half of the enzyme’s active sites are full

33
Q

Kcat

A

measures the number of substrate molecules turned over per enzyme molecule per second

Vmax=[E]Kcat

34
Q

catalytic efficiency

A

Kcat/Km; a large Kcat or a small Km will result in higher catalytic efficiency

35
Q

Lineweaver-Burk plots

A

-1/Km is the intercept of the line and the x-axis

1/Vmax is the intercept of the line with the y-axis

36
Q

cooperative enzymes

A
  • represented as a sigmoidal shape
  • have multiple subunits/active sites
  • attachment to one active site can lead the other sites to go from the tense (T) state to the relaxed (R) state
  • detachment from one active site can lead the other states to go from the relaxed (R) state to the tense (T) state
37
Q

Hill’s coefficient

A

portrays if there is cooperative binding or not
Hill’s coefficient > 1, positive cooperative binding
Hill’s coefficient < 1, negative cooperative binding
Hill’s coefficient = 1, no cooperative binding

38
Q

temperature and enzymes

A
  • enzyme-catalyzed reactions tend to double in velocity for every 10 degrees C until optimum temp reached
  • after this optimal temp, activity falls off sharply as they begin to denature at high temps
39
Q

pH and enzymes

A

human enzymes work best around 7.4; work less efficiently lower or higher

40
Q

feedback inhibition

A

once there is enough of a given product, the product binds to the active site of an enzyme, making them unavailable to make more product

41
Q

competitive inhibition

A

involves occupancy of the active site; can be overcome by adding more substrate; no effect to Vmax, but Km is increased

42
Q

noncompetitive inhibition

A

bind to an allosteric site instead on the active site, which induces a change in enzyme conformation; cannot be overcome by adding more substrate; bind equally well to E and ES; lowers Vmax but does not effect Km

43
Q

mixed inhibition

A

same as noncompetitive inhibitor in that in can bind to an allosteric site on both E or ES but has different affinity for each; alters Km, decreases Vmax

44
Q

uncompetitive inhibition

A

bind only to ES complex; lowers Vmax and Km

45
Q

allosteric enzymes

A

have multiple binding sites; alternate between active and inactive forms;

46
Q

allosteric sites

A

sites different from the active sites that bind either activators or inhibitors

47
Q

covalently modified enzymes

A

enzymes can be activated or deactivated by covalent modification, aka phosphorylation

48
Q

glycosylation

A

covalent attachment of sugar to an enzyme

49
Q

zymogens

A

enzymes are secreted as zymogens; regulatory domain must be removed in order for active site to be exposed

MCAT Biochemistry (5 decks)

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