9700 · 8.2
Transport of oxygen and carbon dioxide flashcards
Revision flashcards for Cambridge 9700 Transport of oxygen and carbon dioxide (syllabus 8.2). Flip, recall, then mark a real past-paper question.
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Describe the quaternary structure of haemoglobin.
Haemoglobin is a globular protein made of four polypeptide chains (two alpha and two beta chains). Each chain has a haem prosthetic group containing an iron ion (Fe²⁺) that binds to one oxygen molecule.
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What is formed when oxygen binds to haemoglobin, and what is this process called?
When oxygen binds reversibly to haemoglobin, it forms oxyhaemoglobin (HbO₂). This process is called loading or association.
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What is meant by 'cooperative binding' in haemoglobin?
Cooperative binding is the phenomenon where the binding of one oxygen molecule to a haem group increases the affinity of the remaining haem groups for oxygen, making subsequent binding easier. This results in the S-shaped (sigmoidal) oxygen dissociation curve.
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What is the Bohr effect?
The Bohr effect is the decrease in haemoglobin's affinity for oxygen in the presence of high carbon dioxide concentration and lower pH. This causes the oxygen dissociation curve to shift to the right.
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What physiological conditions cause a rightward shift in the oxygen dissociation curve?
A rightward shift is caused by: 1. Increased partial pressure of carbon dioxide (pCO₂) 2. Decreased pH (increased H⁺ concentration) 3. Increased temperature. These conditions are typical of respiring tissues.
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List the three main ways carbon dioxide is transported in the blood, from most to least common.
1. As hydrogencarbonate ions (HCO₃⁻) in the plasma (~70%). 2. Bound to haemoglobin as carbaminohaemoglobin (~20%). 3. Dissolved directly in the blood plasma (~10%).
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What is the function of the enzyme carbonic anhydrase in red blood cells?
Carbonic anhydrase catalyses the rapid conversion of carbon dioxide and water into carbonic acid (CO₂ + H₂O → H₂CO₃). This reaction is the first step in converting CO₂ into hydrogencarbonate ions for transport.
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Explain the chloride shift.
The chloride shift is an exchange of ions across the red blood cell membrane. As negatively charged hydrogencarbonate ions (HCO₃⁻) diffuse out of the red blood cell into the plasma, negatively charged chloride ions (Cl⁻) move into the red blood cell to maintain electrical neutrality.