Q4 LONG ANSWER 10M ★ High-yield

Classify the trace elements. Describe the functions and deficiency states of zinc, copper, iodine and selenium.

Biochemistry · 1st Professional — Pre-Clinical

Trace elements = minerals required in amounts of less than 100 mg per day, forming less than 0.01% of body weight.

Group	Elements
Essential	Iron, zinc, copper, iodine, selenium, manganese, molybdenum, chromium, cobalt, fluoride
Possibly essential	Nickel, silicon, vanadium, tin
Toxic	Lead, mercury, cadmium, arsenic

Cofactor for over 300 enzymes — carbonic anhydrase, alkaline phosphatase, alcohol dehydrogenase, carboxypeptidase, RNA and DNA polymerase, superoxide dismutase
Zinc finger motifs in transcription factors and steroid receptors
Needed for insulin storage in the β cell, and for retinol-binding protein synthesis
Wound healing, immunity, taste, spermatogenesis, growth

Zinc deficiency

Growth retardation and hypogonadism — the classical picture described in Iran and Egypt
Poor wound healing; dermatitis; alopecia
Impaired taste (hypogeusia) and smell
Impaired immunity; diarrhoea
Night blindness unresponsive to vitamin A — because retinol-binding protein cannot be made
Acrodermatitis enteropathica — an inherited defect of zinc absorption; periorificial and acral dermatitis, diarrhoea and alopecia, responding dramatically to zinc

Enzyme	Function	Consequence of deficiency
Caeruloplasmin (ferroxidase)	Oxidises Fe2+ for transferrin binding	Anaemia unresponsive to iron
Cytochrome oxidase	Complex IV of the respiratory chain	Impaired energy production
Lysyl oxidase	Collagen and elastin cross-linking	Vascular fragility, bone abnormality
Tyrosinase	Melanin synthesis	Hypopigmentation
Superoxide dismutase	Antioxidant	Oxidative damage
Dopamine β-hydroxylase	Noradrenaline synthesis	Neurological features

Wilson disease	Menkes disease
Copper accumulation	Copper deficiency
ATP7B defect — failure of biliary excretion	ATP7A defect — failure of absorption
Autosomal recessive	X-linked
Kayser–Fleischer rings, cirrhosis, basal ganglia degeneration, psychiatric change	Kinky (steely) hair, arterial tortuosity, neurodegeneration, hypothermia
Serum caeruloplasmin low; urinary copper high	Serum copper and caeruloplasmin both low
Penicillamine, trientine, zinc	Copper histidine injections; largely ineffective

Element	Function	Deficiency	Excess
Iodine	Thyroid hormone synthesis; requirement 150 µg/day	Goitre, cretinism, hypothyroidism, stillbirth	Iodine-induced hyperthyroidism (Jod-Basedow)
Selenium	Glutathione peroxidase; deiodinase	Keshan disease (cardiomyopathy), Kashin–Beck disease	Selenosis — hair and nail loss, garlic breath
Fluoride	Forms fluoroapatite — resists acid; prevents caries	Dental caries	Dental and skeletal fluorosis

Iodine deficiency is the commonest preventable cause of mental retardation worldwide; prevented by universal salt iodisation
Fluorosis is endemic in parts of Rajasthan, Andhra Pradesh, Gujarat and Punjab, from high fluoride in groundwater; the optimum level in drinking water is 0.5–1 ppm

Element	Role	Note
Manganese	Mitochondrial SOD, arginase, pyruvate carboxylase	Deficiency rare; toxicity causes a parkinsonian syndrome in welders
Molybdenum	Xanthine oxidase, sulphite oxidase	Deficiency causes neurological damage
Chromium	Glucose tolerance factor — potentiates insulin	Deficiency impairs glucose tolerance
Cobalt	Constituent of vitamin B12	Useful only as B12
Magnesium	Cofactor for all ATP-requiring enzymes; over 300 enzymes	Deficiency causes tetany and refractory hypocalcaemia

Zinc supplementation reduces the duration and severity of childhood diarrhoea and is recommended by WHO alongside ORS — one of the best-established uses of a trace element
Wilson disease must be excluded in any young person with unexplained liver disease or a movement disorder; it is treatable, and fatal if missed
Trace element deficiency occurs in prolonged parenteral nutrition unless deliberately supplied
Zinc treats Wilson disease by inducing intestinal metallothionein, which traps copper in the enterocyte, so it is shed with the cell — one metal used against another
Copper deficiency should be suspected in anaemia that does not respond to iron, particularly after bariatric surgery or with excessive zinc supplementation
Excessive supplementation is harmful — zinc impairs copper absorption, iron impairs zinc absorption, and selenium is toxic in modest excess
Chromium as glucose tolerance factor is widely marketed for diabetes; benefit is confined to genuine deficiency, which is rare

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