Nutrition Basics — Set 3

Correct Answer: B. Vitamin C

• **Vitamin C (ascorbic acid)** = essential cofactor for prolyl and lysyl hydroxylase enzymes that cross-link collagen triple helices; without it, collagen is structurally weak. • **Scurvy symptoms** — bleeding gums, perifollicular hemorrhages, corkscrew hairs, poor wound healing, and joint pain all stem from defective connective tissue; severe cases cause fatal hemorrhage. • Scurvy devastated sailors on long voyages until James Lind's 1747 trial showed citrus juice could cure it. • 💡 Option A (Vitamin A) is wrong because vitamin A deficiency causes night blindness and xerophthalmia, not collagen breakdown; Option C (Vitamin D) is wrong because vitamin D deficiency causes rickets and osteomalacia due to poor bone mineralization; Option D (Vitamin B) is wrong because the various B-vitamin deficiencies cause pellagra, beriberi, or anemia — not bleeding gums.

Correct Answer: A. Storing energy in the liver

• **Glycogen** = a highly branched polymer of glucose stored mainly in the liver (~100 g) and muscles (~400 g), acting as the body's short-term carbohydrate energy reserve. • **Rapid release** — liver glycogen is broken down by glycogenolysis to replenish blood glucose during fasting; muscle glycogen is used locally for immediate ATP production during exercise. • The branching of glycogen allows simultaneous release from many chain ends, providing a burst of glucose precisely when needed. • 💡 Option B (Protecting organs) is wrong because organ protection is provided by adipose tissue cushioning and ribcage/skeletal structure; Option C (Carrying oxygen) is wrong because oxygen transport is performed by hemoglobin in red blood cells; Option D (Building muscles) is wrong because muscle tissue is synthesized from amino acids (dietary protein), not from glycogen.

Correct Answer: A. Proteins

• **Proteins** = digested into amino acids that are absorbed and reassembled into new structural, enzymatic, and regulatory proteins needed for cellular growth, maintenance, and repair. • **Essential amino acids** — nine of the twenty amino acids (histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine) must come from food because human cells cannot synthesize them. • Positive nitrogen balance — when protein intake exceeds breakdown — is essential during growth, pregnancy, and recovery from injury. • 💡 Option B (Minerals) is wrong because minerals activate enzymes and maintain electrolyte balance but cannot be polymerized into new tissue; Option C (Fats) is wrong because they serve primarily as energy storage, insulation, and membrane components, not tissue construction; Option D (Carbohydrates) is wrong because they are the body's preferred energy source, not a structural material for tissues.

Correct Answer: A. Vitamin A

• **Retinol (Vitamin A)** = the preformed, biologically active alcohol form of vitamin A found in animal products like liver, fish oils, eggs, and dairy. • **Retinal cycle** — retinol is oxidized to retinal in photoreceptor cells, where it combines with opsin protein to form rhodopsin, the pigment enabling vision in dim light. • Vitamin A also regulates gene expression during embryonic development, immune function, and maintenance of epithelial surfaces. • 💡 Option B (Vitamin B1) is wrong because it is called thiamine, a coenzyme for pyruvate dehydrogenase; Option C (Vitamin D) is wrong because it is called calciferol, the sunshine vitamin regulating calcium; Option D (Vitamin E) is wrong because it is called tocopherol, a fat-soluble antioxidant protecting cell membranes.

Correct Answer: C. Vitamin D

• **Vitamin D (calcitriol)** = stimulates intestinal calcium and phosphate absorption; without it, the body cannot mineralize osteoid matrix, leaving bones soft and pliable. • **Age-dependent presentation** — in growing children the result is rickets (bowed legs, delayed fontanelle closure, rachitic rosary on ribs); in adults the already-formed skeleton softens, causing osteomalacia with bone pain and fractures. • Vitamin D deficiency remains globally prevalent, especially in veiled populations, dark-skinned individuals, and those in northern latitudes. • 💡 Option A (Vitamin C) is wrong because its deficiency causes scurvy — collagen failure and bleeding — not poor bone mineralization; Option B (Vitamin K) is wrong because it activates clotting factors and osteocalcin but its deficiency does not cause rickets; Option D (Vitamin A) is wrong because its deficiency causes night blindness and xerophthalmia, not skeletal softening.

Correct Answer: B. Iron

• **Iron (Fe²⁺)** = the central metal ion of the heme prosthetic group in hemoglobin; its ability to reversibly bind and release O₂ without being oxidized to Fe³⁺ is what makes oxygen transport possible. • **Iron deficiency anemia** — insufficient iron reduces hemoglobin synthesis, resulting in microcytic hypochromic anemia with fatigue, pallor, and reduced work capacity; it is the most common nutritional deficiency worldwide. • Dietary heme iron (from meat) is absorbed more efficiently (~25%) than non-heme iron from plants (~5%). • 💡 Option A (Copper) is wrong because copper is needed for the enzyme ceruloplasmin that converts Fe²⁺ to Fe³⁺ for transport, not as the heme-center atom; Option C (Iodine) is wrong because it is incorporated into thyroid hormones T3 and T4, not hemoglobin; Option D (Calcium) is wrong because it provides skeletal hardness and triggers muscle contraction, not blood oxygen transport.

Correct Answer: B. Vitamin B12

• **Vitamin B12 (cobalamin)** = synthesized only by certain bacteria and archaea; it accumulates in animal tissues (liver, meat, dairy, eggs) because animals eat bacteria or food contaminated with bacteria — plants contain none. • **Critical roles** — B12 is required for the methionine synthase reaction (DNA methylation) and methylmalonyl-CoA mutase (fatty acid and amino acid catabolism); its deficiency causes megaloblastic anemia and subacute combined degeneration of the spinal cord. • Strict vegetarians and vegans must supplement B12, as do elderly people with reduced gastric acid needed to cleave it from food proteins. • 💡 Option A (Vitamin B1) is wrong because thiamine is widely found in whole grains, legumes, and nuts — plant sources are adequate; Option C (Vitamin C) is wrong because it is abundant in citrus fruits, bell peppers, and berries — exclusively plant foods; Option D (Vitamin K) is wrong because K1 (phylloquinone) is synthesized by plants in their chloroplasts and is found in leafy greens.

Correct Answer: A. Thiamine

• **Thiamine (Vitamin B1)** = an essential cofactor for three key enzymes: pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, and transketolase — all central to carbohydrate and energy metabolism. • **Two forms of beriberi** — dry beriberi causes peripheral neuropathy (numbness, muscle weakness); wet beriberi causes dilated cardiomyopathy and edema; Wernicke-Korsakoff syndrome is its neurological form seen in alcoholics. • Polished white rice lacks thiamine (removed with the bran), making rice-dependent populations especially vulnerable. • 💡 Option B (Tocopherol) is wrong because tocopherol is vitamin E — the fat-soluble membrane antioxidant; Option C (Calciferol) is wrong because calciferol is vitamin D — the sunshine vitamin for calcium regulation; Option D (Riboflavin) is wrong because riboflavin is vitamin B2 — required for FAD and FMN coenzymes in cellular respiration.

Correct Answer: C. Cellulose

• **Cellulose** = a linear beta-1,4-glycosidic polymer of glucose forming the rigid cell wall of plants; humans lack cellulase enzyme, so it passes through undigested, adding bulk to stools. • **Dietary fiber role** — cellulose slows intestinal transit, regulates blood-sugar spikes by slowing glucose absorption, and feeds colonic bacteria that produce short-chain fatty acids like butyrate. • Cotton fiber is nearly pure cellulose — a fact that illustrates how structurally different it is from digestible starches despite both being glucose polymers. • 💡 Option A (Protein) is wrong because roughage is plant structural material, not a nitrogen-containing amino-acid polymer; Option B (Sugar) is wrong because simple sugars (glucose, fructose, sucrose) are rapidly digested carbohydrates and are not considered roughage; Option D (Starch) is wrong because starch is a digestible alpha-1,4-glycosidic glucose polymer used by plants for energy storage, readily broken down by amylase.

Correct Answer: B. Vitamin E

• **Vitamin E (alpha-tocopherol)** = a fat-soluble antioxidant that intercalates into cell membranes and donates a hydrogen atom to lipid peroxy radicals, terminating the chain reaction of lipid peroxidation. • **Skin protection** — shields polyunsaturated fatty acids in skin cell membranes from UV-induced oxidative damage; also regenerated by vitamin C after donating its electron. • Rich dietary sources include wheat germ oil, sunflower seeds, almonds, and avocado. • 💡 Option A (Vitamin A) is wrong because retinol regulates vision and epithelial differentiation but acts via nuclear receptors, not membrane free-radical quenching; Option C (Vitamin D) is wrong because calciferol functions as a hormone regulating calcium and phosphate balance, not as a membrane antioxidant; Option D (Vitamin K) is wrong because phylloquinone/menaquinone activates clotting factors and osteocalcin via carboxylation reactions, not antioxidant activity.