Chapter 6- The Behavior of Proteins: Enzymes Flashcards

1
Q

catalysis

A

the process of increasing the rate of chemical reactions

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2
Q

enzymes

A
  • biological catalysts, usually globular proteins with self-splicing RNA as the only exception
  • can increase the rate of a reaction by a factor of 10^20
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3
Q

standard free energy (changeG)

A

the difference between the energies of reactants and products under standards conditions

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4
Q

do enzymes alter the equilibrium constant of a reaction or free energy change?

A

nope

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5
Q

activation energy

A

the energy required to start a reaction

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6
Q

what type of reaction has a higher activation energy?

uncatalyzed or catalyzed

A

uncatalyzed (so the rate is slower)

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7
Q

sponanteous reactions have what type of delta g

A

negative

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8
Q

transition state

A

intermediate stage in a reaction where old bonds break and new bonds form

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9
Q

what happens to the rate of a chemical reaction when you increase temperature?

A

goes faster

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10
Q

isoenzymes

A

multiple forms of an enzyme that catalyze the same overall reaction but have subtle physical and kinetic parameters

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11
Q

rate constant

A

a proportionality constant in the equation that describes the rate of a reaction

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12
Q

exponents in the rate equation are determined…

A

experimentsally

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13
Q

first order

A

described a written whose rate depends on the first power of the concentration of a single reactant

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14
Q

second order

A

describes a reaction whose rate depends on the product of the concentrations of two reactants

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15
Q

zero order

A
  • refers to a reaction that proceeds at a constant rate, independent of the concentration of reactant
  • sometimes depends on catalysts
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16
Q

substrate

A

-reactant in an enzyme-catalyzed reaction

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17
Q

where does the substrate bind? and by what type of interactions?

A

enzyme; noncovalent

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18
Q

active site

A

part of enzyme where substrate binds and reactant takes place

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19
Q

why does substrate bind to enzyme

A

because of highly specific interactions between the substrate and the side chains and backbone groups of the amino acids making up the active site

20
Q

lock and key model

A

substrate and active site exactly match each other in shape

21
Q

induced fit model

A

binding of the substrate induces a conformational change in the enzyme that results in a complementary fit after substrate is bound

22
Q

MM rate constant Eqn Terms

A

k1: rate constant for formation of ES
k-1: rate constant for ES–> E + S
k2: rate constant for ES—> E + P

23
Q

rate depends on

A

substrate concentration

24
Q

Vmax

A

maximum velocity

25
Km
- substrate concentration at which the reaction performs at one half its vmax - inverse measure of the affinity of the enzyme for the substrate - equals the concentration of substrate at which 50% of the enzyme active sites are occupied by substrate
26
lower Km=
higher affinity of enzyme for substrate
27
steady state
formation of ES complex equals the rate of its breakdown
28
michealis constant
Km; a numerical value for strength of binding of a substrate to an enzyme
29
michealis-menten eqn formula
V= Vmax [S] ________ Km + [S]
30
When [S]=Km, then...
V= Vmax [S] ________ [S] + [S] and V= Vmax ______ 2
31
what type of curve describes the rate of a nonallosteric enzymatic reaction?
hyperbolic
32
Lineweaver-Burk Double Reciporcal Plot
- graphical method for analyzing the kinetics of enzyme-catalyzed reaction - x axis: 1/[S]= (nm)-1 - y axis: 1/Vo= sec/nm - slope: Km/Vmax
33
Keq=
[E][S] _____ [ES]
34
larger Km
less tightly enzyme bound to substrate
35
turnover number (kcat)
- number of moles of substrate that react per second per mole of enzyme - assumes enzyme is fully saturated with substrate and reaction is proceeding at max rate
36
chymotrypsin
- proteolytic enzyme that preferentially hydrolyzes amide bonds (peptide bonds) adjacent to aromatic amino acid residues - can cleave peptide bonds - catalyzes hydrolysis of ester bonds - hyperbolic
37
ATCase
- allosteric enzyme that catalyzes an early reaction in pyrimidine biosynthesis - signmodial
38
ATCcase and hemoglobin are
allosteric proteins (myoglobin and chymotprsin aren't)
39
inhibitor
substance that decreases the rate of enzyme catalyzed reaction
40
reversible inhibtor
can bind enzyme and then be released, leaving enzyme in original condition
41
irreversible inhibitor
reacts with enzyme to produce protein that is not enzymatically active and from which the original enzyme can't be regenerated
42
compettive inhibitor
- decreases enxyme activity caused by binding of substrate in active site - inhibitor competes with substrate for active site - SLOPE CHANGES - KM INCREASES
43
how can competitive inhibition be overcame?
very high substrate concentration
44
noncompetitive inhibitor
- substrate binds to place other than the active site, but distorts active site so that reaction is inhibited - SLOPE CHANGES - VMAX DECREASES
45
Uncomepetitive inhibitor
- inhibitor can bind to ES, but no free E - lines are parallel - Vmax decreased - apparent Km decreased
46
irrevisible inhibition
covalent binding of an inhibitor to an enzyme, causing permanent inactivation
47
suicide substrates (trojan horse)
molecules used to bind to an enzyme irreversibly and inactivate it