Q.15 An oxyhemoglobin molecule contains ?
l. Protein + heme with iron + C02
2. Protein + Chlorophyll with magnesium +02
3. Lipid + Sugar + O2
4. Heme with iron + 02 + Protein
Oxyhemoglobin is the oxygen-bound form of hemoglobin, a key protein in red blood cells responsible for oxygen transport. The correct answer to the multiple-choice question is option 4: Heme with iron + O₂ + Protein.
Question Breakdown
This MCQ tests knowledge of oxyhemoglobin’s molecular composition, a core concept in molecular biology and human physiology for exams like GATE Life Sciences.
Option Analysis
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Option 1: Protein + heme with iron + CO₂
Incorrect. Hemoglobin includes protein (globin) and heme with iron (Fe²⁺), but oxyhemoglobin specifically binds O₂, not CO₂. CO₂ is transported differently, mainly as bicarbonate or bound to globin amino groups. -
Option 2: Protein + Chlorophyll with magnesium + O₂
Incorrect. Chlorophyll with magnesium is the pigment in plant photosynthesis for light capture, not animal oxygen transport. Oxyhemoglobin uses heme’s iron, not chlorophyll. -
Option 3: Lipid + Sugar + O₂
Incorrect. No lipids or sugars form oxyhemoglobin; it’s a protein-based structure. Lipids and sugars play roles elsewhere, like membranes or energy storage. -
Option 4: Heme with iron + O₂ + Protein
Correct. Oxyhemoglobin consists of four globin protein subunits, each with a heme group (porphyrin ring + Fe²⁺) reversibly bound to one O₂ molecule, enabling oxygen delivery to tissues.
Introduction to Oxyhemoglobin Structure
The oxyhemoglobin molecule contains a precise combination of protein, heme with iron, and oxygen (O₂), making it essential for oxygen transport in blood. This hemoglobin-oxygen complex forms in lungs and releases O₂ in tissues, a process critical for respiration and often tested in molecular biology. Understanding its composition helps in exams and grasping human physiology.
Detailed Composition
Oxyhemoglobin is a tetramer: two alpha and two beta globin protein chains, each linked to a heme prosthetic group. Heme features a porphyrin ring with central Fe²⁺ iron that binds O₂ reversibly—up to four O₂ per molecule. The iron shifts slightly upon binding, stabilizing the “relaxed” state for efficient transport.
Why Oxygen Binding Matters
Fe²⁺ in heme binds O₂ in an “end-on bent” geometry, aided by a distal histidine. This cooperative binding creates a sigmoidal dissociation curve, optimizing O₂ delivery under varying partial pressures. Deoxygenated form (deoxyhemoglobin) is tense; oxyhemoglobin is relaxed.
Common Exam Misconceptions
Options like CO₂ or chlorophyll confuse transport (CO₂) with unrelated pigments (chlorophyll). Lipids/sugars are irrelevant—focus on heme’s iron for O₂ affinity. For competitive exams, memorize: oxyhemoglobin = globin protein + 4 heme-Fe + 4 O₂.
