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Biochemistry

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Enzymes

Question
15 out of 79
 

Km decreases but Vmax same —enzyme is



A Competitive
B Non — competitive

C Irreversible
D Uncompetitive

Ans. A competitive

(Note — question is wrong, please correct it for competitive inhibition km ed and Vmax-same)

Enzyme inhibition:

1. Competitive inhibition —

a. Reversible

b. Inhibitor and substrate resemble each other in structure

c. Inhibitor binds to active site of enzyme

d. Vmax is same (constant)

e. Km is increased.

f. Complex is E-I, inhibitor cannot binds with E-S complex.

g. When the conc. of substrate is increased, the effect of inhibitor can be reversed, forcing it out

form E-I complex.

Enzyme

Substrate

Competitive inhibitor

• Lactate dehydrogenase

Lactate

Oxalate

• Succinate dehydrogenase

Succinate

Malonate

• Xanthine oxidase

Hypoxanthine

Allopurinol

• Folate synthetase

PABA

Sulfonamides

• Fe/ate reductase

Folic acid

Methotrexate

2. Non — competitive Inhibition

a. Reversible or Irreversible

b. Inhibitor and substrate does not resemble each other in structure

c. Inhibitor does not binds the active site

d. Vmax is lowered

e. Km is unaltered (constant)

f. Inhibitor can binds with E-S - complex

Both competitive and non-competitive inhibition— follows Michaelis-Menten equation (Hyperbolic

curve)

3. Allosteric Inhibition: Give a sigmoid kinetics: a mixed kind of inhibition when a inhibitor

binds to the enzyme at a site other than the active site but an a different region in the enzyme called allosteric site.

Types -

a. K-enzymes eg. Aspartate carboxylase and phosphofructokinase Km but Vmax is constant.

b. M-Enzymes eg. Acetyl Co-A carboxylase: - Vmax and Km is constant.

Enzymes Flashcard List

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