1.2.4Unit 1: Lifestyle, Transport, Genes and Health
The Role of Haemoglobin — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 4 parts Lesson 16 of 29 Unit quiz
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 4Haemoglobin and Oxygen Transport
Structure
- Structure Haemoglobin is a globular protein with four polypeptide chains, each carrying a haem group containing an iron ion.
Oxygen carrying
- Oxygen carrying Each haem can bind one oxygen molecule, so one haemoglobin molecule can carry up to four oxygen molecules.
Loading
- Loading In the lungs, where the partial pressure of oxygen is high, haemoglobin picks up oxygen to form oxyhaemoglobin.
Unloading
- Unloading In respiring tissues, where the partial pressure of oxygen is low, oxyhaemoglobin releases its oxygen.
Cooperative binding
- Cooperative binding Binding of the first oxygen alters the shape of haemoglobin so that further oxygen molecules bind more easily.
Section 2 of 4The Oxygen Dissociation Curve
1
The curve plots percentage saturation of haemoglobin with oxygen against the partial pressure of oxygen, and is S-shaped.
2
At low partial pressures the curve is shallow, since the first oxygen molecule binds with difficulty.
3
It then rises steeply because cooperative binding makes the remaining oxygen molecules bind easily.
4
At high partial pressures the curve levels off as haemoglobin becomes almost fully saturated.
5
A curve further to the left means higher affinity for oxygen, and a curve further to the right means that oxygen is released more readily.
Section 3 of 4Variations in Affinity
Variations in Affinity
Bohr effect
- Bohr effect High carbon dioxide concentration lowers the pH and shifts the curve to the right, so more oxygen is unloaded in active tissues.
Fetal haemoglobin
- Fetal haemoglobin Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin, so its curve is to the left.
Why this helps
- Why this helps At the placenta oxygen is transferred from maternal haemoglobin, which releases it, to fetal haemoglobin, which loads it.
Carbon dioxide transport
- Carbon dioxide transport Most carbon dioxide is carried as hydrogencarbonate ions in the plasma, with smaller amounts dissolved or bound to haemoglobin.
Section 4 of 4Exam Checklist & Tips
1.2.4 – Key Points for the Exam
- Haemoglobin The red, iron-containing protein in red blood cells that carries oxygen.
- Oxyhaemoglobin Haemoglobin combined with oxygen.
- Affinity How readily haemoglobin binds to oxygen.
- Bohr effect The shift of the dissociation curve to the right at high carbon dioxide concentration.
Common Mistakes
- Saying that a curve shifted to the left releases oxygen more easily; it holds on to oxygen more tightly.
- Describing the curve as linear when it is S-shaped because of cooperative binding.
- Stating that haemoglobin has two haem groups; it has four.
- Writing that carbon dioxide binds at the haem groups in the same place as oxygen.
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