Vitamins and Coenzymes Questions and Answers

Answer: D

The fat-soluble vitamin is retinol.

Retinol is vitamin A. The fat-soluble vitamins are A, D, E and K; they are absorbed with dietary fat and stored in the liver and fatty tissue.

Thiamine (B1), riboflavin (B2) and nicotinamide (a form of niacin, B3) are B-complex vitamins, which are water soluble.

Answer: A

The scientific name of vitamin A is retinol.

Retinol is the fat-soluble alcohol form of vitamin A. Its derivative retinal forms rhodopsin, the visual pigment of the rods, which is why deficiency causes night blindness before it damages the cornea (xerophthalmia).

The other three are water-soluble B vitamins: thiamine is B1 (deficiency causes beriberi), riboflavin is B2, and niacin is B3 (deficiency causes pellagra).

Answer: D

The disease is pellagra.

Pellagra is caused by deficiency of niacin (vitamin B3), the precursor of NAD and NADP. Its features are the 'three Ds': dermatitis on sun-exposed skin, diarrhoea and dementia. It occurred where maize, poor in available niacin and tryptophan, was the staple food, and nicotinamide or nicotinic acid cures it.

Pernicious anaemia is caused by vitamin B12 deficiency (through lack of intrinsic factor), megaloblastic anaemia by B12 or folate deficiency, and marasmus by overall energy and protein starvation.

Answer: B

The molecule is a coenzyme.

A coenzyme is a small organic, non-protein molecule that binds an enzyme and carries chemical groups, atoms or electrons from one reaction to another: NAD⁺ carries hydride, coenzyme A carries acyl groups, and tetrahydrofolate carries one-carbon units. Many are derived from vitamins.

Cofactor is the broader term that also covers inorganic metal ions, so it does not fit 'organic' specifically. A catalyst is the enzyme's own role, and the substrate is the molecule acted on.

Answer: C

The vitamin is Vitamin C (ascorbic acid).

Prolyl hydroxylase converts proline residues in procollagen to hydroxyproline, using iron, oxygen and 2-oxoglutarate. Ascorbate keeps the enzyme's iron in the reduced ferrous state. Hydroxyproline is needed for hydrogen bonds that stabilise the collagen triple helix, so in vitamin C deficiency collagen is weak and the result is scurvy: bleeding gums, poor wound healing and fragile blood vessels.

Vitamin A works in vision and epithelial differentiation, the B vitamins as coenzymes in energy metabolism, and vitamin D in calcium absorption; none is the cofactor for proline hydroxylation.

Answer: D

The vitamin is Ascorbic acid (vitamin C).

Ascorbic acid is a six-carbon lactone, a sugar acid closely related to glucose: plants and most animals make it from glucose via glucuronate and gulonolactone. Humans lack the last enzyme, L-gulonolactone oxidase, so they need it in the diet. It is water soluble and is not part of the B complex.

Pantothenic acid (B5), biotin (B7) and niacin (B3) are all members of the B complex, so they are excluded by the question's 'non-B complex'. None of them resembles a monosaccharide: pantothenic acid is an amide of pantoic acid and beta-alanine, biotin a fused ring with sulphur, and niacin a pyridine carboxylic acid.