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Biochemistry

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Enzymes

Question
2 out of 79
 

Following is an example of competitive enzyme blockage, except:



A Thymidylate synthase by 5FU

B DHFR by methotrexate

C Cyclooxygenase by aspirin

D Coagulation by dicumarol

Ans. C Cyclooxygenase by Aspirin

Competitive inhibition: Km is high but Vmax is same and Reversible Eg.

a. Lactate deHase by oxamate

b. Aconitase by Trans Fluroacetate

c. Succinate deHase by Malonate

d. HMG-CoA-Reductase by HMG

e. Dihydrofolate Reductase by Amethopterin and Trimethoprim

f. Xanthine oxidase by Allopurinol

g. Folate synthetase by Sulfonamides

h. Folate reductase by Methotrexate

i. Monoamine oxidase by MAO — inhibitors

j. Acetylcholine esterase by physostigmine

k. Vit. K by Dicumarol (Anti coagulant)

l. Antimetabolites eg. they competitively inhibit utilization of normal substrate or get themselves incorporated forming dysfunctional macromolecules:-

A. Methotrexate competitively inhibits DHFA (folate antagonist)

B. Purine antagonists eg. 6-MP, Thioguanine and Azathioprine

C. Pyrimidine Antagonist Eg.

1. 5- Fluorouracil is converted in the body to the corresponding nucleotide 5-fluoro-2-deoxy-uridine monophosphate which inhibit thymidylate synthetase

2. Cytarabine: inhibitor of DNA Polymerase blocks generation of cytidilic acid (s-phase specific)

Non-competitive Inhibition

a. Reversible or Irreversible

b. Vmax Lowered and km unaltered.

Aspirin inhibit COX, nonselective and Irreversible i.e. Non-competitive inhibition

Enzymes Flashcard List

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