Biochem L4

Question 1

Explain what the enzymes are and how they function in biological systems.

Answer 1

• Enzymes are protein catalysts that increase the velocity of chemical reaction.
• all chem. creations in body mediated by enzymes.

Question 2

List the advantages of the enzyme compartmentalization within the cell.

Answer 2

• Isolate reaction, from other competing reactions.
• Provide favorable environment for reaction
• Organize enzymes into purposeful pathways

Question 3

Discuss the mechanism of enzyme action to accelerate chemical reactions.

Answer 3

???

Question 4

Explain the difference between holoenzymes and apoenzymes.

Answer 4

Holoenzymes is a complex enzyme consist of two parts, 1. a protein called apoenzyme.
2. a cofactor ( non-protein)
( can be loosely-bond-coenzyme)
(tightly bond-prosthetic group)

Question 5

Explain the difference between holoenzymes and apoenzymes.

Answer 5

Holoenzymes is a complex enzyme consist of two parts, 1. a protein called apoenzyme.
2. a cofactor ( non-protein)
( can be loosely-bond=coenzyme)
(tightly bond=prosthetic group)

Question 6

List the functional groups involved in enzymatic catalysis.

Answer 6

• Amino acids found in active site, are Serine in active site, trypsin, chymotrypsin.
• Gastric protease (pepsin) has aspartate in active site

Question 7

Define the role of coenzymes in catalysis.

Answer 7

Coenzymes usually produced from vitamins. 2 Major classes of coenzymes; Activaiton-Transfer coenzyme : form covalent bond with substrate.
Oxidation-reduction Coenzymes: no covalent bond with substrate.
????

Question 8

Define the role of coenzymes in catalysis.

Answer 8

Coenzymes usually produced from vitamins, participate in catalytic reactions. 2 Major classes of coenzymes; Activaiton-Transfer coenzyme : form covalent bond with substrate.
Oxidation-reduction Coenzymes: no covalent bond with substrate.
????

Question 9

Explain the difference between functional and dietary vitamin deficiencies and list at least two diseases resulted from the vitamin deficiency.

Answer 9

Functional vitamin deficiency:

• caused by inhibition of coenzyme synthesis.
• Failure of intracellular transport

Dietary vitamin deficiency:
-Inadequate vitamin intake due to either its lack in the diet or problems with its absorption

• thiamin deficiency : beriberi
• PLP forms covalent intermediate with amino group of AAs transamination reaction can cause sideroblastic anemia.

Question 10

Know the functions of metal ions in catalysis and the mechanisms of heavy metal toxicity.

Answer 10

-Metal ions assist in substrate binding.
-They can accept and donate electrons
-Participate in coenzyme binding to enzyme:
*Mg2+ required for binding of phosphate groups of coenzymes to enzyme.
*ATP is usually bound to enzyme through Mg2+
*Zn2+ participate in catalysis by interacting with : alcohol molecule in alcohol dehydrogenase active site.
and CO2 in carbonic anhydrase active site.

_______heavy metal toxicity__

• Heavy Metals toxicity is caused by tight binding of metals to a functional groups of enzymes.
• MERCURY : can bind with selenium required in a reductase reaction, is inactivation can increase cellular oxidative damage and tissue damage.
• LEAD: Inhibit by placing themselves in the normal functional metal spot in the enzyme.
• ALLUMINUM: interferes with iron transport by binding to transferrin and albumin that can cause anemia.

Question 11

Explain how pH and temperature affect the efficiency of enzymatic reactions.

Answer 11

Different enzymes show different responses to changes in temp. and pH.

ex. Gastric peptidase ( pepsin) is active in low pH
ex. Trypsin in pancreatic peptidase active in slightly acidic pH.

Question 12

Describe the use of inhibitors to regulate enzymatic activity.

Answer 12

Inhibitors decrease the rate of enzymatic reaction.

ex. Allopurinol is a suicide inhibitor of the enzyme xanthine oxidase

Question 13

Explain the effect of competitive and noncompetitive inhibitors on the kinetic of enzymatic reactions.

Answer 13

Competitive inhibitor:
Specifically at the catalytic site, where it competes with substrate for binding. Inhibition is reversible by substrate.
____Kinetic effect _____
(Vmax is unchanged )
(Km as defined by S required for 1/2 maximal activity, is increased.)

Noncompetitive inhibitor: Binds E or ES complex other than at the catalytic site. Substrate binding unaltered, but ESI complex cannot form products. Inhibition cannot be reversed by substrate.
_____(Kinetic effect)______
(Km appears unaltered)
(Vmax is decreased proportionately to inhibitor concentration.)

Question 14

Define the mechanism-based inhibition.

Answer 14

• Penicillin forms a covalent bond with the active-site serine of glycopeptidyl transferase thereby inactivating enzyme.
• Allopurinol is an irreversible or “suicide” inhibitor of xanthine oxidase that decreases urate production and is used in treatment of gout.
• Organophosphorus toxins ( nerve gas Sarin) form covalent intermediate with acetylcholinesterase.
• The formed serine-intermediate cannot be hydrolyzed by water.
• Aspirin – covalently acetylates active site of cyclooxygenase (COX), which is a key enzyme in prostaglandin synthesis.
• It permanently inhibits COX-1, a constitutively expressed in all tissues.
• It changes substrate specificity of COX-2, which is an inducible form of the enzyme.

Question 15

Know the differences between covalent and transition-state inhibitors.

Answer 15

???? Could be that transition state analogous bind more tightly than substrate or product.