Enzymes

Question 1

enzymes

Answer 1

biological catalysts that are unchanged by the reactions they catalyze and are reusable
lower the activation energy necessary for biological reactions
do NOT alter the free energy (∆G) or enthalpy (∆H) change that accompanies the reaction nor the final equilibrium position; rather they change the rate (kinetics) at which equilibrium is reached
each catalyzes a single reaction or type of reaction with high specificity

Question 2

oxidoreductases

Answer 2

catalyze redox reactions that involve transfer of electrons

Question 3

transferases

Answer 3

move a functional group from one molecule to another molecule

Question 4

hydrolases

Answer 4

catalyze cleavage with the addition of water

Question 5

lyases

Answer 5

catalyze cleavage without the addition of water and without the transfer of electrons
reverse reaction (synthesis) often more important biologically

Question 6

isomerases

Answer 6

catalyze the interconversion of isomers, including both constitutional isomers and stereoisomers

Question 7

ligases

Answer 7

responsible for joining two large biomolecules, often of the same time

Question 8

exergonic reactions

Answer 8

release energy, ∆G is negative

Question 9

active site

Answer 9

site of catalysis of an enzyme

Question 10

lock and key theory

Answer 10

explains binding to active site

hypothesizes that the enzyme and substrate are exactly complementary

Question 11

induced fit model

Answer 11

explains binding to active site

hypothesizes that the enzyme and substrate undergo conformational changes to interact fully

Question 12

cofactors/coenzymes

Answer 12

metal cation or small organic molecule that allows an enzyme to be active

Question 13

saturation kinetics

Answer 13

as substrate concentration increases, the reaction rate does as well until a maximum value is reached

Question 14

Michaelis-Menten plot

Answer 14

represents relationship between substrate concentration and reaction rate as a hyperbola

Question 15

Lineweaver-Burk plot

Answer 15

represents relationship between substrate concentration and reaction rate as a line

Question 16

cooperative enzymes

Answer 16

display sigmoidal curve because of the change in activity with substrate binding

Question 17

feedback inhibition

Answer 17

regulatory mechanism whereby the catalytic activity of an enzyme is inhibited by the presence of high levels of a product later in the same pathway

Question 18

reversible inhibition

Answer 18

characterized by the ability to replace the inhibitor with a compound of greater affinity or to remove it using mild laboratory treatment

Question 19

competitive inhibition

Answer 19

results when the inhibitor is similar to the substrate and binds to the active site
can be overcome by adding more substrate
vmax is unchanged, Km increases

Question 20

noncompetitive inhibition

Answer 20

results when the inhibitor binds with equal affinity to the enzyme and enzyme-substrate complex
vmax is decreased, Km is unchanged

Question 21

mixed inhibition

Answer 21

results when the inhibitor binds with unequal affinity to the enzyme and the enzyme-substrate complex
vmax is decreased, Km is increased or decreased depending on if the inhibitor has a higher affinity for the enzyme or enzyme-substrate complex

Question 22

uncompetitive inhibition

Answer 22

results when the inhibitor binds only with the enzyme-substrate complex
Km and vmax both decrease

Question 23

irreversible inhibition

Answer 23

alters the enzyme in such a way that the active site is unavailable for a prolonged duration or permanently; new enzyme molecules must be synthesized for the reaction to occur again

Question 24

allosteric sites

Answer 24

can be occupied by activators which increase either affinity or enzymatic turnover

Question 25

phosphorylation/glycosylation

Answer 25

covalent modification with phosphate/carbohydrate

can alter the activity or selectivity of enzymes

Question 26

zygomens

Answer 26

secreted in inactive form and are activated by cleavage