Chapter 6- The Behavior of Proteins: Enzymes

Question 1

catalysis

Answer 1

the process of increasing the rate of chemical reactions

Question 2

enzymes

Answer 2

• 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

Question 3

standard free energy (changeG)

Answer 3

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

Question 4

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

Answer 4

nope

Question 5

activation energy

Answer 5

the energy required to start a reaction

Question 6

what type of reaction has a higher activation energy?

uncatalyzed or catalyzed

Answer 6

uncatalyzed (so the rate is slower)

Question 7

sponanteous reactions have what type of delta g

Answer 7

negative

Question 8

transition state

Answer 8

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

Question 9

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

Answer 9

goes faster

Question 10

isoenzymes

Answer 10

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

Question 11

rate constant

Answer 11

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

Question 12

exponents in the rate equation are determined…

Answer 12

experimentsally

Question 13

first order

Answer 13

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

Question 14

second order

Answer 14

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

Question 15

zero order

Answer 15

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

Question 16

substrate

Answer 16

-reactant in an enzyme-catalyzed reaction

Question 17

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

Answer 17

enzyme; noncovalent

Question 18

active site

Answer 18

part of enzyme where substrate binds and reactant takes place

Question 19

why does substrate bind to enzyme

Answer 19

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

Question 20

lock and key model

Answer 20

substrate and active site exactly match each other in shape

Question 21

induced fit model

Answer 21

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

Question 22

MM rate constant Eqn Terms

Answer 22

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

Question 23

rate depends on

Answer 23

substrate concentration

Question 24

Vmax

Answer 24

maximum velocity

Question 25

Km

Answer 25

• 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

Question 26

lower Km=

Answer 26

higher affinity of enzyme for substrate

Question 27

steady state

Answer 27

formation of ES complex equals the rate of its breakdown

Question 28

michealis constant

Answer 28

Km; a numerical value for strength of binding of a substrate to an enzyme

Question 29

michealis-menten eqn formula

Answer 29

V= Vmax [S]
________
Km + [S]

Question 30

When [S]=Km, then…

Answer 30

V= Vmax [S]
________
[S] + [S]

and

V= Vmax
______
2

Question 31

what type of curve describes the rate of a nonallosteric enzymatic reaction?

Answer 31

hyperbolic

Question 32

Lineweaver-Burk Double Reciporcal Plot

Answer 32

• 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

Question 33

Keq=

Answer 33

[E][S]
_____
[ES]

Question 34

larger Km

Answer 34

less tightly enzyme bound to substrate

Question 35

turnover number (kcat)

Answer 35

• 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

Question 36

chymotrypsin

Answer 36

• 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

Question 37

ATCase

Answer 37

• allosteric enzyme that catalyzes an early reaction in pyrimidine biosynthesis
• signmodial

Question 38

ATCcase and hemoglobin are

Answer 38

allosteric proteins (myoglobin and chymotprsin aren’t)

Question 39

inhibitor

Answer 39

substance that decreases the rate of enzyme catalyzed reaction

Question 40

reversible inhibtor

Answer 40

can bind enzyme and then be released, leaving enzyme in original condition

Question 41

irreversible inhibitor

Answer 41

reacts with enzyme to produce protein that is not enzymatically active and from which the original enzyme can’t be regenerated

Question 42

compettive inhibitor

Answer 42

• decreases enxyme activity caused by binding of substrate in active site
• inhibitor competes with substrate for active site
• SLOPE CHANGES
• KM INCREASES

Question 43

how can competitive inhibition be overcame?

Answer 43

very high substrate concentration

Question 44

noncompetitive inhibitor

Answer 44

• substrate binds to place other than the active site, but distorts active site so that reaction is inhibited
• SLOPE CHANGES
• VMAX DECREASES

Question 45

Uncomepetitive inhibitor

Answer 45

• inhibitor can bind to ES, but no free E
• lines are parallel
• Vmax decreased
• apparent Km decreased

Question 46

irrevisible inhibition

Answer 46

covalent binding of an inhibitor to an enzyme, causing permanent inactivation

Question 47

suicide substrates (trojan horse)

Answer 47

molecules used to bind to an enzyme irreversibly and inactivate it