lecture 4: Enzymes as catalysts

Question 1

RNAs that act as enzymes called?

Answer 1

Ribozymes

Question 2

Turnover Number

Answer 2

Substrate to product per second

Question 3

What enzymes catalyze oxidation-reduction reactions?

Answer 3

Oxidoreductases

Question 4

What enzymes catalyze transfer of C, N, or P containing groups?

Answer 4

Transferases

Question 5

What enzyme catalyze cleavage of bonds by addition of water?

Answer 5

Hydrolases

Question 6

What enzymes catalyze cleavage of CC, CS and CN bonds?

Answer 6

Lyases

Question 7

What enzymes catalyze rearrangement of bonds

Answer 7

Isomerases

Question 8

What enzymes catalyze formation of bonds between carbon and O, S, N coupled to hydrolase (glue to other parts of molecule)

Answer 8

Ligases

Question 9

What are holoenzymes?

Answer 9

complex enzymes with 2 parts: protein component-apoenzyme or cofactor that could be coenzyme or prosthetic group

Question 10

What is beneficial about compartmentalization of enzymes?

Answer 10

1. Isolate
2. Provide favorable environment
3. Organize into purposeful pathways

Question 11

Isoenzymes and examples?

Answer 11

Different enzymes that catalyze the same reaction.
Ex. Low Km Hexakinase (High affinity)
High Km Glucokinase (Low affinity)

Question 12

Proenzymes/zymogens? example?

Answer 12

inactive precursor enzymes, cleaved to activate.

Ex. blood coagulation cascade

Question 13

Activation-transfer coenzymes vs oxidation-reduction coenzymes

Answer 13

Activation-transfer form covalent bonds with substrate

Oxidation-reduction do not form covalent bonds, donate or accept electrons (NAD, FAD)

Question 14

What enzyme catalyzes oxidation of ethanol, active site contains Zn2+, requires NAD+ for oxidation

Answer 14

ADH (Alcohol dehydrogenase)

Question 15

What enzyme converts acetaldehyde (the product of ethanol oxidation, responsible for liver disease from alcoholism) to acetate

Answer 15

ALDH (Acetaldehyde dehydrogenase)

Question 16

How does alcohol cause fatty liver?

Answer 16

ADH is inhibited by excess NADH, NADH also is not allowed to oxidize fatty acids that will build up in liver.

Question 17

How does penicillin work as inhibitor?

Answer 17

It forms covalent bond with active site serine of glycopeptidyl transferase, inactivating the enzyme

Question 18

How does allopurinol work as an inhibitor?

Answer 18

It works as irreversible or “suicide inhibitor” of xanthine oxidase that decreases urate inhibitor and is used in treatment of gout.

Question 19

How does organophosphorus (nerve gas) work as an inhibitor?

Answer 19

form covalent intermediate with acetylcholinesterase. Meaning that excess acetylcholine is in the cell

Question 20

How does aspirin work as an inhibitor?

Answer 20

covalently acetylates active site of cyclooxygenase (COX), which is a key enzyme in prostaglandin synthesis

Question 21

Explain each Heavy Metal Toxicity (Inhibitors)
Hg
Pb
Al
Fe

Answer 21

Hg: reacts with selenium required for such selenoenzymes as thioredoxin reductase, which is involved in antioxidant activity.

Pb: is an example of a metal that inhibits by replacing normal functional metal in the enzyme.
Its toxicity may be caused by replacement of Ca2+ in calmodulin and protein kinase C

Al: interferes with iron transport by binding to transferrin and albumin that can cause anemia.

Fe: overload can lead to iron toxicity because high concentration of iron can cause liver failure.