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8. Porphyrins and Haemoproteins — Biochemistry MCQs
KEMU · 113 MCQs with clinical pearls · Prof Jariya
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Sections in this kemu
- Haem Structure — 13 MCQs
- Jaundice — 9 MCQs
- Haemoglobin Structure — 9 MCQs
- Heme Catabolism — 7 MCQs
- Haemoglobin Variants — 7 MCQs
- Thalassaemia — 7 MCQs
- Iron Deficiency Anaemia — 7 MCQs
- Porphyrias — 6 MCQs
- Megaloblastic Anaemia — 6 MCQs
- Allosteric Regulation — 5 MCQs
- Oxygen Dissociation Curve — 5 MCQs
- Haemolytic Anaemia — 5 MCQs
- Oxygen Binding — 4 MCQs
- Sickle Cell Disease — 4 MCQs
Sample MCQs with clinical pearls
A neonate with physiological jaundice receiving phototherapy is likely to have decreased activity of which of the following enzymes required for bilirubin clearance?
A) ALA synthase
B) Bilirubin UDP-glucuronosyl transferase ✔
C) Biliverdin reductase
D) Haem oxygenase
E) Porphobilinogen deaminase
PHOTOTHERAPY converts bilirubin → LUMIRUBIN (water-soluble structural isomer) and PHOTOBILIRUBIN → these can be excreted in bile and urine WITHOUT hepatic conjugation → BYPASSES the requirement for BILIRUBIN UDP-GLUCURONOSYL TRANSFERASE (UGT1A1). Therefore phototherapy effectively DECREASES THE NEED for UGT1A1 activity. This is why phototherapy works in Crigler-Najjar Type II (reduced but not absent UGT1A1) — phototherapy + residual UGT1A1 maintains acceptable bilirubin levels.
📹 [VIDEO LINK]
A 12-year-old boy presents with jaundice and bone pains after a hiking trip. His peripheral blood smear shows anaemia consistent with haemolysis. Bilirubin production in this boy is likely to be which of the following?
A) Equal to normal at 250mg per day
B) Greater than 100mg per day
C) Greater than 300mg per day ✔
D) Less than 100mg per day
E) Less than 300mg per day
NORMAL bilirubin production = ~250-300 mg/day. HAEMOLYTIC ANAEMIA → increased RBC destruction → bilirubin production GREATER THAN 300 mg/day → unconjugated hyperbilirubinaemia. Elevated urinary urobilinogen. No bilirubin in urine (unconjugated not water-soluble). Hiking trip = possible sickle cell crisis or G6PD-induced haemolysis.
📹 [VIDEO LINK]
A medical student studying haemoglobin structure notes that haem must be protected from oxidation to maintain iron in the ferrous state. The alpha helices of a globin subunit form an oxygen binding pocket with which of the following property?
A) Hydrophilic
B) Hydrophobic ✔
C) Ionic
D) Polar
E) Positively charged
The OXYGEN BINDING POCKET is HYDROPHOBIC. This hydrophobic environment: (1) EXCLUDES WATER → prevents oxidation of Fe²⁺ to Fe³⁺ (water is needed for spontaneous Fe²⁺ oxidation → methaemoglobin formation). (2) Allows O₂ to bind reversibly to Fe²⁺. (3) Forces CO to bind at an angle (distal histidine tilts CO → reduces CO affinity from theoretical 25,000× to ~250× greater than O₂). Without the hydrophobic pocket: Fe²⁺ would be rapidly oxidised to Fe³⁺ → methaemoglobin → no O₂ transport.\
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📹 [VIDEO LINK]
113 MCQs are arranged to the learning outcomes of this kemu.
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