Enzymes

Question 1

Ser-proteases

Answer 1

Consist only of proteins (ser=one a.a.)

• Trypsin
• chymotrypsin
• elastase
• acetylcholin esterase

Question 2

Cofactors

Answer 2

Bound to enzymes.

-Metal ions (ion-sulfur clusters, Zn, carbonic anhydrase)

Question 3

Coenzymes

Answer 3

Intermed. carrier of e-, specific atoms or funct.gr.

-Water sol. vit. derivates (NAD+, PALP, TPP)

Question 4

Haloenzyme

Answer 4

Enzyme+coenzyme

Question 5

Apoenzyme

Answer 5

Enzyme-coenzyme

Question 6

Prosthetic groups

Answer 6

Tightly bound organic cofactors

• FAD
• NAD+, NADH+H+

Question 7

Serine proteases

Answer 7

Hydrolyse peptide bonds of proteins

• Chymotrypsin
• Trypsin
• Elastin

Question 8

Major enzymes prod. by pancreas

Answer 8

• Chymotrypsin
• Trypsin
• Elastin

Question 9

Substrate binding site of Chymotrypsin

Answer 9

Ser-189, Gly-216

Question 10

Substrate binding site of Trypsin

Answer 10

Asp-189, Gly-216

Question 11

Substrate binding site of Elastase

Answer 11

Ser-189, Val-216

Question 12

Inhibition of ser-proteases

Answer 12

At Ser-195 by diisopropylphospho-fluoridate DIPF

Question 13

Mechanism of enzyme action

Answer 13

Michaelis-Munten theory

E+S ES E+P

Question 14

Activation energy

Answer 14

Free energy between initial and transitional state

Question 15

Factors affecting enzyme activitiy

Answer 15

• Non-specific: affecting velocity at each enzymatic reaction (temp, pH, denaturation)
• Specific: affecting only certain Es/certain groups of Es (conc. of reactants, inorganic effectors, organic effectors)

Question 16

Michaelis constant - Km

Answer 16

Km is the substrate conc. at which the velocity of the reaction is half the max. value -> the E is saturated in 50% by substrate.

Question 17

Enzyme inhibitors

Answer 17

-Non-specific -> denaturation: acid&bases, temp., alcohol, heavy metals, red. agents
-Specific
1.Irreversible: Ser-proteases, SH-containing E´s (heavy metals), cytochrome oxidase (CN-ions)
2.Reversible: bound to other than S-site
a)Competetive: sim. as S, bound to S-binding site
B)Non-competetive: bound to another part of the E. Allosteric, feedback

Question 18

Controlling enzyme action

Answer 18

1. Regulation of its conc. by repressing/inducing its synthesis
2. Red. by inhibitors/incr. by effectors: allosteric phosphorylation, zymogen, isoenzymes, modulator proteins (CAP)

Question 19

Gene induction

Answer 19

Turning on of transcription = incr. mRNA prod.

Question 20

Gene repression

Answer 20

Turning off of transcription = drcr. mRNA prod.

Question 21

Allosteric regulation

Answer 21

The molec. bind to an allosteric site, sep. from the active site, and inhib./stim. the enzyme activity

Question 22

Feedback inhibition

Answer 22

A type of allosteric regulation. The final product is an allosteric inhib. of the first enzyme in the pathway.

Question 23

Phosphorylation

Answer 23

Covalent modification of an enzyme, by addition of a specific funct. gr. -> activate/inhib. the enzyme

Question 24

Zymogen activation

Answer 24

Covalent modification of an enzyme.

• Zymogen=proenzyme; inactive precursor form of enzyme
• Activation site=site of cleavage
• Activated by specific regulatory protease

Question 25

Isoenzymes

Answer 25

Differ slightly in aa. sequence and consequently in catalytic properties. Have diff. Km.

• Isoform A: high Km-works best in tissues w. high S-conc.
• Isoform B: low Km-works best in tissues w. low S-conc.

Question 26

Oxidoreductases

Answer 26

One oxidiced, one reduced

Question 27

Transferases

Answer 27

Transfer groups.

1. Aldehyde-, ketotransferase
2. Acyltransferase
3. Aminotransferase
4. Phosphotransferase
5. C1 fragments

Question 28

Hydrolases

Answer 28

Hydrolytic cleavage of diff. bonds.

1. Esterases
2. Glycosidases
3. Peptidases
4. Amidases

Question 29

Lyase synthase

Answer 29

Elimination/addition, without breakdown of ATP

Question 30

Isomerases

Answer 30

Isomerization

Question 31

Lyase synthetase

Answer 31

(ATP). Joining of two molecules, without breakdown of atp.