This set of Drug Biotechnology Questions and Answers for Experienced people focuses on “Phase 1 Reactions – 2”.
1. Which one is the rate-limiting step in the oxidation of xenobiotics?
a) Binding of the substrate to Fe3+
b) Electron transfer from NADPH to the above complex
c) The enzyme-substrate complex combines with a molecule of oxygen forming a ternary complex
d) Ternary complex gains an electron from the NADPH
Explanation: The rate-limiting step is the transfer of an electron from NADPH to the complex of substrate and cytochrome 450. The gaining of an electron by cytochrome 450 reduces the Fe3+ to Fe2+. This step is considered the rate-limiting step of the oxidation of xenobiotics.
2. What provides the atom of oxygen for making of water?
a) From the cytochrome 450
b) From the environment
c) From the activated oxygen P-450 substrate complex
d) From cytochrome reductase
Explanation: One atom of oxygen from the activated oxygen P450 complex is transferred to the substrate to yield the oxidized product and the other atom forms water. The free oxidized form of cytochrome P-450 is ready to attach to another molecule of substrate.
3. What is the major end product of oxidation of aromatic carbon atoms?
d) Arene oxide
Explanation: The oxidation of aromatic carbon atoms proceeds via formation of a reactive intermediate arene oxide. This arene oxide in most cases is converted into arenols and in some cases produces minor products such as catechols and glutathione conjugates.
4. Which one of the following is reactive and a known carcinogenic?
a) Cytochrome P-450
d) Arene oxide
Explanation: The oxidation of aromatic carbon atoms proceeds via formation of a reactive intermediate arene oxide. This arene oxide is a known carcinogenic or even cytotoxic in some instances.
5. Which of the following is not a common N containing functional groups which undergo reduction reactions?
a) Nitro compounds
b) Azo compounds
c) N-oxide compounds
d) Nitrite compounds
Explanation: The N-containing functional groups that commonly undergo bioreduction are nitro, azo, N-oxide compounds. Reduction of the nitro group proceeds via formation of nitroso and hydroxylamine intermediates to yield amines.
6. Esters on hydrolysis yields alcohol and carboxylic acid.
Explanation: Esters on hydrolysis yield alcohol and carboxylic acids with the release of a water molecule. The reaction is catalysed by esterase.
7. Which enzymes catalyses the hydrolysis of amides?
Explanation: The reaction of hydrolysis of amides is catalysed by amidases. The reaction involves C-N bond cleavage thus yielding carboxylic acid and amine. Amides are hydrolysed slowly in comparison to esters.
8. What is the end product of hydrolysis of Lidocaine?
a) 2, 6-Xylidine, N, N-Dimethylglycine
b) 2, 5- Xylidine, Dimethylglycine
c) Xylidine, glycine
d) 1, 6-Xylidine
Explanation: The reaction of hydrolysis of amides is catalysed by amidases. Lidocaine is a secondary amide with an organic substituent on N-atom. Thus providing us with 2, 6-Xylidine, N, N-Dimethylglycine as the end product.
9. What is the end product of hydrolytic dehalogenation of DDT?
a) Dichloro diphenyl ethylene
b) 1- chloro diphenyl dichloroethylene
c) Trichloro triphenyl trichloroethylene
d) Dichloro diphenyl dichloroethylene
Explanation: In the hydrolytic dehalogenation a molecule of HCL is removed from the substrate. Thus in case of Dichloro diphenyl trichloroethane when a molecule of HCL is removed we get Dichloro diphenyl dichloroethylene as the product.
10. What does the hydrolysis of Aspirin yield us with?
a) Salicylic acid only
b) Salicylic acid and CH3COOH
d) Succinic acid
Explanation: Esters like aspirin with large alcoholic and small acidic group when hydrolysed in the presence of esterase yields us with salicylic acid and CH3COOH as the end product.
Sanfoundry Global Education & Learning Series – Drug and Pharmaceutical Biotechnology.
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