Enzyme Kinetics & Inhibition

Question 1

enzyme

Answer 1

catalysts that speed up the rate of reaction by lowering the activation energy without being changed themselves; virtually all enzymes are proteins although some catalytically active RNAs exist

Question 2

Gibbs free energy of activation

Answer 2

the difference in free energy between the substrate and transition state that must be overcome for the reaction to proceed; the transition state has the highest free energy in the pathway

Question 3

Free energy change (delta G)

Answer 3

difference in energy level between the product and substrate

• negative = spontaneous
• positive = unfavorable and non-spontaneous

Question 4

substrate binds the active site of the enzyme by what kinds of forces?

Answer 4

• multiple weak forces such as electrostatic interactions, H-bonds, van der Waals, and hydrophobic ineractions
• in some cases also reversible covalent bonds

Question 5

oxidoreductases

Answer 5

transfer electrons

-ex: dehydrogenases

Question 6

transferases

Answer 6

transfer of a functional group from one molecule to another

-ex: hexokinase

Question 7

hydrolases

Answer 7

break bonds by adding water

-ex: trypsin

Question 8

lyases

Answer 8

cleave bonds without the addition of water

-ex: pyruvate decarboxylase

Question 9

isomerases

Answer 9

transfer of groups within a molecule

-ex: maleate isomerase

Question 10

ligases

Answer 10

responsible for joining two large biomolecules (often of the same type)…bond formation coupled to ATP hydrolysis
-ex: pyruvate carboxylase

Question 11

synthase vs. synthetases

Answer 11

synthetases require high energy phosphates (such as ATP or GTP) to catalyze bond formation, whereas synthases do not

Question 12

isoenzymes

Answer 12

different forms of an enzyme which catalyze the same reaction, but which exhibit different physical or kinetic properties

Question 13

the shape of the resulting graph when V0 is plotted against [S]

Answer 13

hyperbolic curve

Question 14

cooperative enzymes show what kind of curve?

Answer 14

sigmoidal

Question 15

irreversible inhibitors

Answer 15

bind tightly, often covalently, and permanently inactivate the enzyme

Question 16

Michaelis-Menten equation

Answer 16

V0 = (Vmax * [S]) / (Km + [S])

Question 17

LB plots

Answer 17

used for determining Vmax and Km by measuring V0 at different [S] by plotting 1/V0 against 1/[S] in a double reciprocal plot
intercept on the y-axis = 1/Vmax
intercept on the x-axis = -1/Km
slope = Km/Vmax

Question 18

two amino acids susceptible to irreversible inhibition

Answer 18

Ser and Cys which have reactive -OH and -SH groups respectively

Question 19

competitive inhibitor

Answer 19

similar to substrate and binds at active site
increases Km (leaves Vmax unchanged)
can be overcome by increasing [S]

Question 20

noncompetitive inhibitor

Answer 20

binds E and ES with equal affinity
decreases Vmax (leaves Km unchanged)

Question 21

mixed inhibitor

Answer 21

binds E and ES with unequal affinity
decreases Vmax
may alter Km depending on if the inhibitor has higher affinity for E or ES

Question 22

uncompetitive inhibitor

Answer 22

binds ES complex only
Km and Vmax both decrease because it prevents ES complex from dissociating (thus creates stronger affinity between E and S in complex which lowers Km)

Question 23

phosphorylation

Answer 23

covalent modification with a phosphate that alters activity or selectivity of enzymes
alters tertiary structure of enzyme

Question 24

glycosylation

Answer 24

covalent modification with carbohydrates that alters activity or selectivity of enzymes

Question 25

zymogen activation

Answer 25

irreversible hydrolysis of one or more peptide bonds