Haemoglobin and Oxygen Transport MCQs

55 MCQs with clinical pearls · MBBS Biochemistry · Prof Jariya

Topics covered (9)

Haem Structure — 13 MCQs
Haemoglobin Structure — 9 MCQs
Haemoglobin Variants — 7 MCQs
Thalassaemia — 7 MCQs
Allosteric Regulation — 5 MCQs
Oxygen Dissociation Curve — 5 MCQs
Oxygen Binding — 4 MCQs
Sickle Cell Disease — 4 MCQs
Methaemoglobinaemia — 1 MCQs

Sample MCQs with clinical pearls

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.\ \ 📹 [VIDEO LINK]

Which of the following coordinates with ferrous iron directly in the haem pocket?

A) Distal histidine

B) Lateral histidine

C) Proximal histidine ✔

D) Terminal histidine

E) Valine residue

PROXIMAL HISTIDINE (His-F8): coordinates DIRECTLY with Fe²⁺ via the 5th coordination bond (below the porphyrin plane). In deoxyHb: Fe²⁺ sits ABOVE the porphyrin plane (large atomic radius) → proximal His pulled out of plane. Upon O₂ binding: Fe²⁺ moves INTO porphyrin plane (smaller covalent radius) → proximal His moves with it → conformational change propagates through the tetramer → T→R transition (molecular basis of cooperativity).\ \ 📹 [VIDEO LINK]

Which of the following stabilises oxygen binding in the haem pocket via a hydrogen bond with oxygen?

A) Distal histidine ✔

B) Lateral histidine

C) Proximal histidine

D) Terminal histidine

E) Valine residue

DISTAL HISTIDINE (His-E7): forms a HYDROGEN BOND with O₂ after it binds to Fe²⁺. Does NOT coordinate with Fe²⁺ directly (that is the proximal histidine). Functions: (1) STABILISES O₂ binding via hydrogen bonding. (2) REDUCES CO AFFINITY by forcing CO to bind at an angle (CO normally binds Fe²⁺ linearly with very high affinity; distal His tilts CO → reduces affinity from 25,000× to ~250× greater than O₂). This discrimination between O₂ and CO is physiologically critical.\ \ 📹 [VIDEO LINK]

These are three of 55 MCQs in this section. Every question carries a clinical pearl explaining the reasoning.

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