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MCAT biochem > Enzymes > Flashcards

Enzymes Flashcards

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MCAT flashcards
1
Q

enzymes

A

biological catalysts that speed up the rate of a reaction by lowering the energy of activation
- sensitive to temp, pH, and are specific for specific reactions

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2
Q

what happens to enzymes during a reaction?

A

they are not changed or consumed and do not effect Keq/ equillibrium of a reaction or affect thermodynamic perameters

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3
Q

can enzymes make an unfavorable reaction favorable?

A

no because they do not affect ΔG, ΔS or ΔH

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4
Q

t/f: enzymes can increase the rate of a reaction

A

true

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5
Q

t/f: enzymes can alter equilibrium

A

false

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6
Q

t/f: enzymes reduce the activation energy (Ea)

A

True

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7
Q

t/f: enzymes can change Δh, Δg, Δs

A

false

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8
Q

t/f: enzymes are sensitive to temp and pH

A

true

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9
Q

t/f enzymes are consumed during a reaction

A

false

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10
Q

reaction coordinate diagram

A

shows how the reactants progress to products and how much gibbs free energy changes

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11
Q

activation energy

A

the amount of energy needed to overcome for a reaction to proceed

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12
Q

what direction do enzymes speed up a reaction

A

forward and backward (avoid altering equillibrium)

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13
Q

where does an enzyme interact with substrate

A

at the active site

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14
Q

active site

A

binding site: where substrate binds via intermolecular forces and catalytic site of enzyme

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15
Q

orthosteric regulators

A

interact with an enzyme at its active site

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16
Q

allosteric regulators

A

bind somewhere besides the active site

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17
Q

lock and key theory

A

active site of an enzyme and the substrate fit together like a puzzle with no change in terciary or quartenary structure
- old and outdated model

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18
Q

induced fit model

A

enzyme and substrate are seen as affecting one another. the initial binding causes a conformational shift

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19
Q

oxidoreductases

A

catalyze electron transfer reactions
- example –> dehydrogenases

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20
Q

transferase

A

transfer a functional group between molecules
ex: dna polymerase

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21
Q

hydrolase

A

catalyze hydrolysis
- lactase (add water to break apart)
- proteases

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22
Q

lyases

A

cleave bonds through non-hydrolysis mechanisms
- pyruvate decarboxylase

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23
Q

pyruvate decarboxylase

A

enzyme used in fermenting alcohol
pyruvate –> aldehyde via decarboxylation,

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24
Q

isomerases

A

catalyze isomerization
ribose 5 phosphate isomerase

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25
Q

ligase

A

join molecules together with COVALENT bonds
- pyruvate carboxylase

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26
Q

pyruvate carboxylase

A

adds a cooh group to pyruvate to make it oxaloacetate

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27
Q

phosphotases

A

remove phosphates

28
Q

kinases

A

add phosphates

29
Q

rate limiting step of glycolysis`

A

pfk1 making 1,6 fructose bisphosphotate

30
Q

what product DIRECTLY inhibits pfk-1

A

increased ATP levels

31
Q

mechanism of blood clotting

A

positive feedback

32
Q

feed-forward regulation

A

an enzyme is regulated by an upstream product

33
Q

pyruvate kinase activity is increased by what

A

increased levels of fructose 16bisp

34
Q

cooperativity

A

enzyme has multiple active sites and binding at one site facilitates binding at another
- example: hemoglobin

35
Q

what does a cooperativity graph look like

A

sigmoidal (s shaped)
saturation of enzymes (y) and substrate present (x)

36
Q

hill coefficient

A

degree of cooperativity of an enzyme

37
Q

hill coefficient of >1

A

positive cooperativity

38
Q

hill coefficient of <1

A

negative cooperativity (binding of first ligand decreases binding affinity for next)

39
Q

Vmax

A

maximum rate of reaction for an enzyme to convert a specific reactant into product
- all enzymes are saturated
- units of substate/ time

40
Q

Km

A

concentration of substrate where half of the enzymes are saturated (1/2 vmax)
- measures the affinity of an enzyme for a substrate

41
Q

michaelis-mentin equation

A

V = (Vmax[s])/ Km + [s]

42
Q

how does changes in substrate concentration and enzyme affect the km

A

it does not change km

43
Q

linewiever-burke plots

A

x axis is -1/ km
y axis is 1/vmax

44
Q

what happens on a lineweiver burke plot if vmax is decreased

A

the y intercept will move up (farther from 0)

45
Q

what happens on a linweiver burke plot if km is decreased

A

the x intercept will move farther from 0

46
Q

inhibitors

A

reduce the effictive activity of enzymes
- can be reversible or irreversible

47
Q

how do reversible inhibitors interact with enzymes?

A

through non-covalent interactions

48
Q

how do irreversible inhibitors interact with enzymes

A

through covalent interacitons

49
Q

competitive inhibitors

A

reversible
- compete with substrate for binding at the active site
- vmax stays same, km increases
- can be outcompeted by adding more substrate

50
Q

noncompetitive inhibitors

A

reversible inhibitors that bind to an allosteric site
-they can bind to enzyme regardless of whether the substrate is bound or not
- reduce vmax and km remains same

51
Q

uncompetitive inhibitor

A

reversible inhibitor that interacts with the enzyme-substrate complex at an allosteric site
- prevents enzyme from letting go of substrate so catalysis is reduced
- vmax decreased, km decreased

52
Q

mixed inhibition

A

inhibitor can bind to the free enzyme at an allosteric site or the E-S complex
- VMAX ALWAYS DECREASES and effect on km is variable
- if it prefers the active site, km increases
- if it prefers ES complex, km decreases

53
Q

effect of competitive inhibition on vmax and km

A

vmax –> same
km –> increase

54
Q

effect of noncompetitive inhibition on vmax and km

A

vmax –> decreases
km –> stays same =

55
Q

effect of uncompetitive inhibition on vmax and km

A

vmax : decrease
km: decrease

56
Q

what kind of inhibition causes a decrease in Vmax and an increase in KM

A

mixed inhibition where it prefers to bind to free enzyme

57
Q

phosphorylation

A

kinases add a phosphate group
- can be considered activation

58
Q

what amino acid residues are phosphorylated

A

serine, threonine, tyrosine

59
Q

dephosphorylation

A

phopshotases remove phosphate groups
inactivate residue

60
Q

glycosylation

A

add a sugar to a molecule

61
Q

zymogens

A

proenzymes
inactive forms that must be cleaved

62
Q

cofactors

A

inorganic (metal ions) or organic molecules that must be present for an enzyme to function

63
Q

coenzymes

A

organic cofactors (vitamins)

64
Q

prosthetic group

A

coenzymes that are tightly bound to an enzyme
- heme in hemoglobin

65
Q

holoenzyme

A

complete enzyme with cofactors/coenyzmes

66
Q

Kcat

A

turnover rate
number of substrate converted to product per second

67
Q

kcat equation

A

vmax/[E]

MCAT biochem (11 decks)

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