Biochemistry MCQs: Free Radicals and Antioxidants Nutrient

Q-1. Which of the following act as antioxidants?
a) Vit. C
b) Vit. D
c) Selenium
d) Glutathione peroxidase
e) Vit. E

Answer: a, c, d and e
Naturally occurring antioxidants:
Beta carotene and ubiquinone
Ascorbic acid
Vit E or tocopherol
Glutathione peroxidase

Q-2. Which of these have antioxidant properties?
a) Tocopherol
b) Reduced glutathione
c) Citrulline
d) Lycopene

Answer: a, b and d
See above explanation.

Q-3. Which of the following reduces oxidative stress except?
a) Glutathione peroxidase
b) Catalase
c) Xanthine oxidase
d) Ceruloplasmin
e) Super oxide dismutase

Answer: Xanthine oxidase
Xanthine oxidase contains molybdenum and plays an important role in the conversion of purine base to uric acid.

Q-4. Reperfusion injury is caused by
a) Vitamin E
b) Calcium ion
c) Magnesium ion
d) Superoxide ion

Answer: Superoxide ion
Reperfusion of ischemic tissues results in formation of toxic reactive oxygen species, including superoxide anions (O2−), hydroxyl radicals (OH−), hypochlorous acid (HOCl), hydrogen peroxide (H2O2) and peroxy-nitrite derived from NO.

Q-5. During phagocytosis, the metabolic process called respiratory burst involves the activation of
a) Oxidase
b) Hydrolase
c) Peroxidase
d) Dehydrogenase

Answer: Oxidase
The biochemical mechanism of microbial killing and degradation following phagocytosis is called respiratory burst.
The respiratory burst of activated macrophages is increased utilization of glucose via the pentose phosphate pathway to reduce NADP+ to NADPH, and increased utilization of oxygen to oxidize NADPH to produce oxygen radicals as cytotoxic agents to kill phagocytosed micro-organisms.
Important point:
The respiratory burst oxidase (NADPH oxidase) is a flavo-protein that reduces oxygen to super-oxide.

Q-6. Enzyme responsible for respiratory burst reaction
a) Dehydrogenase
b) Peroxidase
c) Hydroxylase
d) NADPH oxidase

Answer: NADPH oxidase
See above explanation.

Q-7. Reactive oxygen intermediates are released by
a) NADPH oxidase
b) Catalase
c) Glutathione peroxidase
d) Super oxide dismutase

Answer: NADPH oxidase
See above explanation.

Q-8. Which of the following elements is known to influence the body’s ability to handle oxidative stress?
a) Calcium
b) Iron
c) Potassium
d) Selenium

Answer: Selenium
The peroxides that are formed by radical damage to lipids in membranes and plasma lipo-proteins are reduced to fatty acids by glutathione peroxidase, a selenium dependent enzyme. This forms oxidized glutathione, which no longer has protective properties.
The oxidized glutathione is reduced by NADPH dependent glutathione reductase.
Important point:
Glutathione (GSH) is a tri-peptide consisting of Glutamic acid, cysteine and glycine.

Q-9. Glutathione peroxidase contains
a) Chromium
b) Manganese
c) Zinc
d) Selenium

Answer: Selenium
See above explanation.

Q-10. All are true about glutathione except: (AIIMS Nov 2008 and May 2008)
a) It converts hemoglobin to methemoglobin
b) It scavenges free radicals and superoxide ions
c) It is tri-peptides
d) It conjugates xenobiotics

Answer: It converts hemoglobin to methemoglobin
See above explanation.
Important point:
A number of potentially toxic electrophilic xenobiotics are conjugated to the nucleophilic GSH. The enzyme catalyzing this reaction is called glutathione-S-transferase and present in high amounts in liver cytosol and in lower amount in other tissues. GSH is an important defense mechanism against certain toxic compounds.