Antioxidants and Free Radicals Quiz

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18 Questions

What is the role of antioxidants in protecting cells?

Preventing damage to cellular components caused by free radicals

How do antioxidants terminate the chain of free radical reactions?

By getting oxidized themselves or removing free radical intermediates

Which classification of antioxidants is based on their solubility?

Water & Fat soluble antioxidants

What is the main function of chelating elements like metals in antioxidant mechanisms?

Preventing the formation of free radicals

Which type of antioxidants include Ascorbic acid, Uric acid, and glutathione?

Water-soluble antioxidants

How are natural and synthetic antioxidants classified?

Based on their source

What happens when a weak bond breaks in a molecule?

It leaves an unpaired electron in the atomic orbital

Which of the following is an example of oxygen-containing free radicals?

Singlet oxygen

What is the primary oxygen radical formed when an oxygen molecule acquires an electron?

Superoxide anion

Which macromolecules of the cell can be damaged by highly unstable and reactive free radicals?


Under what conditions are oxidants formed as normal products of aerobic metabolism in cells?

Under pathophysiological conditions

What is the term used to describe an excited state of O2 in which the spin of one unpaired electron is changed?

Singlet oxygen

What is the tripeptide made up of cysteine, glycine, and glutamine called?

Glutathione (GSH)

Which enzyme can utilize glutathione as a substrate to remove free radicals like hydrogen peroxide?

Glutathione peroxidase

What is considered a biomarker of oxidative stress in conditions like hypertension?

Uric acid

Which antioxidant protects the integrity of erythrocyte membrane by scavenging peroxyl radical and hydroxyl radicals?

Uric acid

Which fat-soluble antioxidant is considered a chain-breaking antioxidant?

Vitamin E

Where are fat-soluble antioxidants normally localized in cells to help protect cell membranes?

Cell membrane

Study Notes

Antioxidants and Free Radicals

Glutathione (GSH)

  • Tripeptide composed of cysteine, glycine, and glutamine
  • Present in all human cell types in reduced form (GSH) and oxidized form (GSSG)
  • Acts as an antioxidant by donating hydrogen atoms and reducing free radicals directly or as a substrate for enzymes like glutathione peroxidase

Uric Acid

  • End product of purine metabolism in humans
  • Last two reactions in uric acid formation generate free radicals, making it a biomarker of oxidative stress in conditions like hypertension
  • Acts as a free radical scavenger, quenching singlet oxygen and scavenging peroxyl and hydroxyl radicals, protecting erythrocyte membrane integrity
  • Major antioxidant in plasma, protecting cells from oxidative damage


  • Chain-breaking antioxidant that becomes oxidized to biliverdin, but can be recycled back to bilirubin by biliverdin reductase
  • Protects cells from oxidative damage

Fat-Soluble Antioxidants

  • Hydrophobic in nature, localized in cell membranes, and protect against lipid peroxidation
  • Examples include vitamins (Vit. A, Vit. E)

Definition and Classification of Antioxidants

  • Molecules that prevent damage to cellular components from free radical reactions
  • Classified based on properties, source, function, and solubility (water-soluble and fat-soluble)
  • Other classification methods include natural and synthetic, enzymatic and non-enzymatic, endogenous and exogenous, and primary and secondary antioxidants

Free Radicals

  • Molecules with unpaired electrons, formed when a weak bond breaks
  • Examples include superoxide anion radicals, nitric oxide radical, singlet oxygen, and hydrogen peroxide
  • Formed as a normal product of aerobic metabolism, but can cause oxidative damage when produced in excess

Test your knowledge on antioxidants and free radicals with this quiz. Learn about the definition of antioxidants and how they protect cells from damage caused by free radicals. Explore the different ways in which antioxidants work in the body.

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