Vitamins and Cofactors Flashcards

Vitamin C (ascorbic acid) acts as an antioxidant primarily by:

Answer: Donating electrons to neutralize free radicals

Ascorbic acid is a potent reducing agent that donates electrons to neutralize reactive oxygen species and can regenerate other antioxidants such as vitamin E.

Vitamin K is required for the gamma-carboxylation of which proteins critical for blood clotting?

Answer: Clotting factors II, VII, IX, and X

Vitamin K-dependent gamma-glutamyl carboxylase modifies prothrombin (factor II) and factors VII, IX, and X, adding extra carboxyl groups that allow Ca²⁺ binding essential for clot formation.

Vitamin D3 (cholecalciferol) is hydroxylated first in the liver to 25-hydroxyvitamin D, then in the kidney to its active form:

Answer: 1,25-dihydroxyvitamin D (calcitriol)

1,25-dihydroxyvitamin D₃ (calcitriol) is the biologically active hormone that binds to nuclear vitamin D receptors to increase intestinal calcium absorption and regulate bone mineralization.

Which fat-soluble vitamin acts as the most important lipid-soluble antioxidant in membranes?

Answer: Vitamin E (alpha-tocopherol)

Vitamin E (alpha-tocopherol) is the primary chain-breaking antioxidant in lipid membranes, donating a hydrogen atom to lipid peroxyl radicals to terminate lipid peroxidation chain reactions.

Folate (Vitamin B9) deficiency causes megaloblastic anemia primarily because folate is required for synthesis of:

Answer: Thymidylate (dTMP) for DNA synthesis

Folate as 5,10-methylene-THF is required for thymidylate synthase to convert dUMP to dTMP; without sufficient folate, DNA synthesis is impaired, causing large, immature red blood cells.

Coenzyme A (CoA) is derived from which vitamin?

Answer: Pantothenic acid (B5)

Coenzyme A contains pantothenic acid (vitamin B5) as a core component, along with adenosine 3',5'-bisphosphate and a phosphopantetheine moiety that provides the reactive thiol group.