Question 1

Which of the following best describes a free radical in the context of biochemistry?

Accepted Answer

A molecule with at least one unpaired electron

Question 2

Which reaction is responsible for the formation of hydroxyl radicals in the presence of iron overload?

Accepted Answer

$$ \mathrm{H_2O_2 + Fe$$^{2+}$$ \rightarrow OH^- + OH^\cdot + Fe$$^{3+}$$} $$

Question 3

Which enzyme catalyzes the dismutation of superoxide to hydrogen peroxide?

Accepted Answer

Superoxide dismutase (SOD)

Question 4

What is the primary antioxidant function of Vitamin E (α-tocopherol) in cell membranes?

Accepted Answer

Chain-breaking antioxidant that protects polyunsaturated fatty acids (PUFAs) from oxidation

Question 5

Which of the following is a key feature of hydrogen peroxide ($$ \mathrm{H_2O_2} ) in $$biological systems?

Accepted Answer

It is membrane-permeable and a precursor to hydroxyl radical

Question 6

Which of the following reactions describes the formation of peroxynitrite ($$ \mathrm{ONOO^-} $$)?

Accepted Answer

$$ \mathrm{NO^\cdot + O_2$^\cdot^- \rightarrow ONOO^-} $$

Question 7

Which antioxidant enzyme requires selenium as a cofactor and incorporates it as selenocysteine in its active site?

Accepted Answer

Glutathione peroxidase (GPx)

Question 8

During a respiratory burst in phagocytes, which compound is produced by myeloperoxidase using hydrogen peroxide and chloride?

Accepted Answer

Hypochlorous acid ($$ \mathrm{HOCl} )$$

Question 9

Which of the following is a biomarker for lipid peroxidation and membrane damage?

Accepted Answer

Malondialdehyde (MDA)

Question 10

Which dietary antioxidant is water-soluble and directly scavenges superoxide, hydroxyl, and peroxyl radicals?

Accepted Answer

Vitamin C (ascorbic acid)

Question 11

Which of the following is NOT a required cofactor for nitric oxide synthase (NOS) activity?

Accepted Answer

Selenium

Question 12

Which antioxidant system converts oxidized glutathione (GSSG) back to its reduced form (GSH) using NADPH?

Accepted Answer

Glutathione reductase

Question 13

Carotenoids primarily act as antioxidants by:

Accepted Answer

Quenching singlet oxygen ($$ \mathrm{^1O_2} ) $$and scavenging peroxyl radicals ($$ \mathrm{ROO^\cdot} )$$

Question 14

Which of the following is a major cellular source of superoxide ($$ \mathrm{O_2$^\cdot^-} ) in $$human cells?

Accepted Answer

Mitochondrial electron transport chain (ETC)

Question 15

Which of the following statements about melatonin is TRUE?

Accepted Answer

It crosses cell membranes and the blood-brain barrier

Question 16

Which of the following is a function of uric acid in plasma?

Accepted Answer

Scavenges hydroxyl radical ($$ \mathrm{OH^\cdot} $$), peroxynitrite ($$ \mathrm{ONOO^-} $$), and singlet oxygen ($$ \mathrm{^1O_2} )$$

Question 17

Which of the following is a consequence of peroxynitrite ($$ \mathrm{ONOO^-} ) $$formation in cells?

Accepted Answer

Protein nitration and mitochondrial DNA damage

Question 18

Which of the following is a chain-breaking antioxidant that acts in the lipid phase and protects cell membranes?

Accepted Answer

Vitamin E (α-tocopherol)

Question 19

Which enzyme is responsible for high-capacity removal of hydrogen peroxide ($$ \mathrm{H_2O_2} ) in $$peroxisomes?

Accepted Answer

Catalase

Question 20

Which of the following is a major subclass of flavonoids?

Accepted Answer

Anthocyanins

Oxidants and Anti-Oxidant Systems: Biochemical Mechanisms and Cellular Protection

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