Enzymes

Question 1

The transfer of electrons between biological molecules (oxidation-reduction rxns) are catalyzed by which enzymes?

Answer 1

Oxidoreductases
-Reductant: e- donor
-Oxidant: e- acceptor
Ex: dehydrogenase, reductase, oxidase

Question 2

The movement of functional groups from one molecule to another are catalyzed by?

Answer 2

Transferases

-Kinases are part of this class (responsible for catalyzing transfer of phosphate group from ATP to another molecule)

Question 3

The breaking of a compound into two molecules by the addition of H2O is catalyzed by which enzymes?

Answer 3

Hydrolases

-Ex: phosphatase, peptidase, nuclease, lipase, and etc.

Question 4

A single molecule being cleaved into 2 products is carried out by which enzymes?

Answer 4

Lyases

-also carries out synthesis of 2 molecules into a single one (synthases)

Question 5

The rearrangement of bonds within a molecule are catalyzed by-?

Answer 5

Isomerases

-Catalyze rxns between stereoisomers and constitutional isomers

Question 6

The synthesis/addition of similar large molecules are catalyzed by which enzymes?

Answer 6

Ligases (often requires ATP)

-Nucleic acid synthesis and repair

Question 7

Some enzymes require non-protein molecules to catalyze a rxn called…?

Answer 7

Coenzymes & cofactors

• Usually kept @ low conc. in cells
• Enzymes w/o: apoenzymes
• Enzymes w/: holoenzymes
• Prosthetic groups: tightly bound cofactors/coenzymes that are necessary for enzyme function

Question 8

Inorganic molecules or metal ions that are generally digested as dietary minerals are?

Answer 8

Cofactors

Question 9

Small organic groups of vitamins or vitamin derivatives are?

Answer 9

Coenzymes

Question 10

What is the only way to increase vmax?

Answer 10

Increase enzyme conc

-Induce expression of gene encoding the enzyme

Question 11

When the rxn rate is = to 1/2 vmax…?

Answer 11

Then Km = [S]

Question 12

The [S] conc at which half the [E]’s active sites are full is referred to as?

Answer 12

Km (michaelis constant)

• Can be a measure of affinity of an enzyme for its substrate
• Intrinsic property=cannot be altered/changed by changes in conc of enzyme and substrate

Question 13

When [S]

Answer 13

Changes in substrate conc will greatly affect the rxn rate

Question 14

When [S]>Km….?

Answer 14

Changes in substrate conc increase much more slowly as it approaches vmax

Question 15

The # of substrate molecules converted to product per enzyme molecule per second is termed?

Answer 15

Kcat

-Typically between 101-103

Question 16

Catalytic efficiency of an enzyme refers to the ratio of…?

Answer 16

Kcat/Km

-Large Kcat or small Km will result in higher catalytic efficiency (more efficient enzyme)opii

Question 17

If Hill’s coeff>1…?

Answer 17

Positive cooperative binding is occuring

-After 1 ligand is bound, the affinity of the enzyme for further ligands increases

Question 18

If Hill’s coeff<1…?

Answer 18

Negative cooperation binding occurs

-After 1 ligand is bound, the affinity for the enzyme for further ligands decreases

Question 19

If Hill’s coeff=1…?

Answer 19

The enzyme doesn’t exhibit cooperative binding

Question 20

Inhibition that involves the occupancy of an enzyme’s active site that can be overridden by adding more substrate is termed?

Answer 20

Competitive Inhibition

• Vmax: no effect
• Km: is increased

Question 21

Inhibition to the allosteric site of an enzyme that causes an irreversible conformational change is termed?

Answer 21

Noncompetitive Inhibition

• Vmax: decreased (less enzyme available to react)
• Kmax: no effect

Question 22

When an inhibitor can bind to an enzyme and enzyme substrate complex, but have different affinity for each is termed?

Answer 22

Mixed inhibition

• Bind on allosteric site
• Km effect varies
• Vmax: decreases

Question 23

Inhibitors that bind only to the enzyme substrate complex and essentially lock the substrate in the complex, preventing its release is termed?

Answer 23

Uncompetitive inhibition

-Vmax and Km: decreases

Question 24

Enzymes that have more than one binding site are termed?

Answer 24

Allosteric enzymes

-Alternate between active and inactive form

Question 25

Dangerous enzymes that need to be highly regulated and controlled are secreted as inactive…?

Answer 25

Zymogens