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Block 3 — Biochemistry MCQs
UHS · 504 MCQs with clinical pearls · Prof Jariya
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Sections in this uhs
- Fatty Acid Structure and Classification — 43 MCQs
- Calcium and Vitamin D — 22 MCQs
- Vitamin A — 22 MCQs
- Eicosanoids — 21 MCQs
- ABG Interpretation — 19 MCQs
- Anion Gap and Delta Ratio — 19 MCQs
- Lipoproteins and Atherosclerosis — 19 MCQs
- Vitamin D — 18 MCQs
- Metabolic Acidosis — 18 MCQs
- Iron Metabolism — 14 MCQs
- Nutritional Significance of Lipids — 13 MCQs
- Lipoproteins and Lipoprotein Disorders — 13 MCQs
- Copper Metabolism — 12 MCQs
- Vitamin D and Calcium — 12 MCQs
Sample MCQs with clinical pearls
A 25-year-old woman from northern latitudes with insufficient ultraviolet light exposure presents with backache and vitamin D levels of 10 ng/mL. Failure of formation of which of the following compounds is the primary precipitating factor for her backache?
A) 1,25 dihydroxycholecalciferol
B) 7-dehydrocholesterol
C) Calcidiol
D) Calcitriol
E) Cholecalciferol ✔
Skin synthesis is the main source of vitamin D: ultraviolet B converts 7-dehydrocholesterol in the epidermis to CHOLECALCIFEROL (vitamin D3). This is then 25-hydroxylated in the LIVER to calcidiol, the storage form measured in blood, and 1-alpha-hydroxylated in the KIDNEY to calcitriol, the active hormone. Deficiency is common at high latitude, with dark skin, with veiling, and in the housebound. MEMORY: 'Skin makes D3, liver adds 25, kidney adds 1.'
An 18-month-old boy is brought for routine check-up. He has a wide anterior fontanelle and is exclusively breastfed with minimal sunlight exposure. Supplementation with which of the following vitamins is most urgently required?
A) Vitamin A
B) Vitamin B12
C) Vitamin D ✔
D) Vitamin E
E) Vitamin K
A wide anterior fontanelle with delayed closure, craniotabes and delayed milestones is RICKETS from vitamin D deficiency. Without calcitriol, intestinal calcium and phosphate absorption falls, so the osteoid laid down at the growth plate cannot mineralise. The skull signs appear first because the calvarium grows fastest in infancy. Alkaline phosphatase is raised and calcium low or low-normal. MEMORY: 'Soft skull in an infant means soft bone everywhere.'
A 1-year-old boy presents with bowing of legs, frontal bossing, and bead-like prominences at the costochondral junctions. His mother reports exclusive breastfeeding for 8 months and avoids taking him outdoors. Which component of his bone extracellular matrix is primarily deficient?
A) Collagen fibrils
B) Elastin fibres
C) Fibronectin networks
D) Glycosaminoglycans
E) Hydroxyapatite crystals ✔
Bone mineral is HYDROXYAPATITE, a crystalline calcium phosphate. In rickets the osteoid matrix is laid down normally but cannot be MINERALISED, because calcium and phosphate are insufficient. The result is soft bone that bends under load - bowed legs - and heaped-up unmineralised cartilage at the costochondral junctions, the RACHITIC ROSARY. Frontal bossing reflects the same failure in the skull. MEMORY: 'The matrix is there; only the crystal is missing.'
504 MCQs are arranged to the learning outcomes of this uhs.
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