2.6.8Inquiry Process
Haemoglobin and Oxygen — IB Biology HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 70 of 160
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 4Structure of Haemoglobin
Quaternary protein
- Quaternary protein Adult haemoglobin is made of four polypeptide chains, two alpha and two beta, held together as a single functional unit.
Haem groups
- Haem groups Each chain carries a haem group containing an iron(II) ion, and each iron can bind one oxygen molecule.
Capacity
- Capacity One haemoglobin molecule can therefore carry up to four O₂ molecules, giving eight oxygen atoms.
Location
- Location Haemoglobin is packed inside red blood cells, which allows blood to carry far more oxygen than it could dissolved in plasma.
Section 2 of 4Cooperative Binding
Binding at one site alters the affinity of the other sites.
1
In the lungs, oxygen partial pressure is high and the first oxygen molecule binds to a haem group relatively slowly.
2
Binding changes the shape of the protein, which makes the remaining haem groups easier to reach.
3
The second and third oxygen molecules therefore bind more readily, a process called cooperativity.
4
The fourth binds somewhat less easily because few binding sites remain available.
5
In respiring tissues, the same effect works in reverse: loss of the first oxygen makes release of the others easier.
Section 3 of 4Comparing Oxygen Carriers
Comparing Oxygen Carriers
Myoglobin
- Myoglobin A single-chain protein in muscle with a high affinity for oxygen that stores oxygen and releases it only when oxygen is very low.
Fetal haemoglobin
- Fetal haemoglobin Has a higher affinity for oxygen than the adult form, so oxygen transfers across the placenta from the mother's blood to the fetus.
Adult haemoglobin
- Adult haemoglobin Has lower affinity than myoglobin, which allows it to unload oxygen in tissues where the partial pressure is low.
Affinity
- Affinity Affinity is the tendency to bind oxygen;
- higher affinity means binding at lower partial pressure and slower release.
| Pigment | Chains | Oxygen affinity |
|---|---|---|
| Adult haemoglobin | 4 | Moderate |
| Fetal haemoglobin | 4 | Higher than adult |
| Myoglobin | 1 | Highest |
Section 4 of 4Exam Checklist & Tips
2.6.8 – Key Points for the Exam
- Haemoglobin The iron-containing protein in red blood cells that transports oxygen.
- Haem group The non-protein iron-containing group that binds oxygen.
- Cooperativity The effect where binding of one oxygen molecule increases the affinity for further oxygen.
- Oxyhaemoglobin Haemoglobin combined with oxygen.
- Affinity The strength of attraction between a protein and a ligand such as oxygen.
Common Mistakes
- Saying haemoglobin has one iron atom; there are four, one per haem group.
- Calling haemoglobin a tertiary protein only; it has quaternary structure.
- Stating that fetal haemoglobin has a lower affinity; it is higher.
- Confusing affinity with capacity, since each haemoglobin still carries at most four O₂ molecules.
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