Chapter 8 ENZYMES: KINETICS

Question 1

the quantitative measurement of the rates of enzyme-catalyzed reactions and the systematic study of factors that affect these rates, constitutes a central tool for the analysis, diagnosis, and treatment of the enzymic imbalances that underlie numerous human diseases

Answer 1

Enzyme kinetics

Question 2

In the blood, the appearance or a surge in the levels of particular enzymes serve as

Answer 2

clinical indicators for pathologies such as myocardial infarctions, prostate cancer, and damage to the liver

Question 3

lists the initial chemical species (substrates) present and the new chemical species (products) formed for a particular chemical reaction, all in their respective proportions or stoichiometry

Answer 3

balanced chemical equation

Question 4

The term often used to designate the reactants whose formation is thermodynamically favored

Answer 4

“products”

Question 5

used to describe reactions in living cells where the products of reaction (2) are immediately consumed by a subsequent enzyme-catalyzed reaction or rapidly escape the cell, for example, CO2

Answer 5

Unidirectional arrows

Question 6

describes in quantitative form both the direction in which a chemical reaction will tend to proceed and the concentrations of reactants and products that will be present at equilibrium

Answer 6

Gibbs free energy (change ΔG)

Question 7

True or False

The sign and the magnitude of the free energy change
determine how far the reaction will proceed.

Answer 7

True

Question 8

True or False

If ΔG^0 is a negative number, Keq will be greater than unity, and the concentration of products at equilibrium will exceed that of the substrates.

Answer 8

True

Question 9

True or False

If ΔG^0 is positive, Keq will be less than unity, and the formation of substrates will be favored.

Answer 9

True

Question 10

is independent of the mechanism of the reaction, and provides no information concerning rates of reactions

Answer 10

ΔG^0

Question 11

The concept of the ____ is fundamental to understanding the chemical and thermodynamic basis of catalysis.

Answer 11

Transition state

Question 12

also called the collision theory—of chemical kinetics states that for two molecules to react they

(1) must approach within bond-forming distance of one another, or “collide,” and
(2) must possess sufficient kinetic energy to overcome the energy barrier for reaching the transition state.

Answer 12

kinetic theory

Question 13

The sum of the molar ratios of the reactants defines the ______ of the reaction.

Answer 13

kinetic order

Question 14

is the factor by which the rate of a biologic process increases for a 10 degree celsius increase in temperature

Answer 14

Temperature coefficient

Question 15

referred to as the variable reactant or substrate, can be determined by maintaining the concentration of the other reactants in large excess over the variable reactant

Answer 15

Kinetic Order

Question 16

True or False

All enzymes accelerate reaction rates by lowering ΔGf for
the formation of transition states.

Answer 16

True

Question 17

Catalysis by enzymes that proceeds via a unique reaction

mechanism typically occurs when the transition state intermediate forms a covalent bond with the enzyme

Answer 17

Covalent Catalysis

Question 18

The rate of almost all enzyme-catalyzed reactions exhibits a

significant dependence on ______.

Answer 18

hydrogen ion concentration

Question 19

Most intracellular enzymes exhibit optimal activity at pH values

Answer 19

between 5 and 9

Question 20

Most measurements of the rates of enzyme-catalyzed reactions employ relatively short time periods, conditions that are considered to approximate ______

Answer 20

initial rate conditions

Question 21

illustrates in mathematical terms the relationship between initial reaction velocity vi and substrate concentration [S]

Answer 21

Michaelis-Menten equation

Question 22

used to determine the kinetic mechanism of an enzyme inhibitor

Answer 22

Lineweaver-Burk plot

Question 23

The activity of impure enzyme preparations typically is

expressed as a

Answer 23

specific activity

Question 24

is an exclusive property of multimeric enzymes that bind substrate at multiple sites

Answer 24

Cooperative Behavior

Question 25

For enzymes that display positive cooperativity in binding

the substrate, the shape of the curve that relates changes in vi to changes in [S] is

Answer 25

Sigmoidal

Question 26

originally derived to describe the cooperative binding of O2 by hemoglobin

Answer 26

Hill equation

Question 27

In Hill equation, If n is greater than 1, the enzyme is said to exhibit

Answer 27

positive cooperativity

Question 28

Compounds that mimic the transition state of an enzyme catalyzed reaction

Answer 28

transition state analogs

Question 29

Compounds that take advantage of the catalytic machinery of an enzyme

Answer 29

mechanism-based inhibitors

Question 30

the inhibitor (I) binds to the substrate-binding portion
of the active site thereby blocking access by the substrate.

Answer 30

competitive inhibition

Question 31

The structures of most classic competitive inhibitors therefore tend to resemble the structure of a substrate, and thus are termed ____

Answer 31

substrate analogs

Question 32

____ acts by decreasing the number of free enzyme molecules available to bind substrate, that is, to form ES, and thus eventually to form product

Answer 32

competitive inhibitor

Question 33

True or False

a competitive inhibitor has no effect on Vmax but raises
K′m, the apparent Km for the substrate.

Answer 33

True

Question 34

is sometimes employed as an alternative to the

Lineweaver-Burk plot for determining inhibition constants.

Answer 34

Dixon plot

Question 35

are substrate analogs that bind to the active site, preventing enzyme-substrate complex formation

Answer 35

Competitive inhibitors

Question 36

substrate analogs transformed by the catalytic machinery of the enzyme into a product that blocks the function of the same catalytic subunit.

Answer 36

Suicide or mechanism based inhibitors

Question 37

bind to the free enzyme and enzyme-substrate complex at the allosteric site and lower the catalytic efficiency of the enzyme.

Answer 37

Simple noncompetitive inhibitors

Question 38

used both to distinguish between competitive and noncompetitive inhibitors and to simplify evaluation of inhibition constants.

Answer 38

Double-reciprocal plots

Question 39

applies to mechanisms in which one or more products are released from the enzyme before all the substrates have been added

Answer 39

Ping-pong

Question 40

involve covalent catalysis and a transient, modified form of the enzyme

Answer 40

Ping-pong reactions

Question 41

Ping-pong Bi-Bi reactions are often referred to as

Answer 41

double displacement reactions

Question 42

are used to complement kinetic analyses and to distinguish between ordered and random Bi-Bi reactions

Answer 42

Product inhibition studies

Question 43

a drug needs to be resistant to degradation by enzymes present in the patient or pathogen

Answer 43

drug metabolism

Question 44

Inhibitor looks like substraye and competes for same active site; Km is increased and Vmax has not changed

Answer 44

Competitive inhibitors

Question 45

Inhibitor binds to another site different from active site; Km not changed; Vmax lowered

Answer 45

Noncompetitive inhibitors

Question 46

Vmax/protein

- to compare impure preparations of same enzyme

Answer 46

Specific Activity

Question 47

Vmax/mol of enzyme; to compare across homogenous enzymes

Answer 47

Turnover Number

Question 48

Vmax/Number of active sites

Answer 48

Catalytic Constant

Question 49

Type of Inhibitoon on HGM-CoA reductase; Dihhdrofolate reductase; Angiotensin converting enzyme

Answer 49

Competitive

Question 50

Type of inhibition in Thymidilate synthase; cyclooxugenase; bacterial transpeptidase and monoamine oxidase

Answer 50

Suicide