L22: Myoglobin & hemoglobin. Allostery

• What are the two types of proteins discussed in the study material?

  Myoglobin and hemoglobin
• What is the primary function of glucose in aerobic respiration?

  Glucose is oxidised for energy
• What is the difference between aerobic and anaerobic respiration in terms of oxygen availability?

  Aerobic respiration requires oxygen, while anaerobic does not
• Why is relying solely on diffusion insufficient for oxygen supply in larger organisms?

  Diffusion would NOT provide sufficient oxygen
• How much oxygen in our blood is carried in solution?

  Only 5% of the oxygen in our blood is carried in solution
• What is the partial pressure of oxygen in metabolising tissues?

  The partial pressure of oxygen in metabolising tissues is approximately 20 torr
• What is the significance of the protein that binds oxygen at 100 torr and releases it at 20 torr?

  It is essential for efficient oxygen transport in the body
• What is the saturation percentage of myoglobin at 20 torr?

  91% saturated
• How does myoglobin ensure a good supply of oxygen to muscles?

  Myoglobin is well adapted to bind oxygen effectively
• What type of binding curve characterizes myoglobin's oxygen binding?

  The curve is hyperbolic, characteristic of simple binding
• What happens if myoglobin were used for oxygen transport?

  Myoglobin would not release oxygen effectively in tissues
• What is the saturation percentage of hemoglobin in the lungs?

  98% saturation
• What is the saturation percentage of hemoglobin in tissues?

  32% saturation
• How does the binding affinity of myoglobin compare to hemoglobin?

  Myoglobin has a higher affinity for oxygen than hemoglobin
• What is the significance of the sigmoidal binding curve of hemoglobin?

  It indicates cooperativity in oxygen binding
• What are the two conformations of hemoglobin subunits?

  T state (tense) and R state (relaxed)
• What does the concerted model of cooperativity suggest?

  It suggests that binding of oxygen shifts the equilibrium between T and R states
• What does the sequential model of cooperativity imply?

  Binding of ligand changes the conformation of subunits, increasing affinity
• What happens to the structure of hemoglobin when oxygen is bound?

  The structure changes, bringing the helix closer to heme
• How does the central cavity of hemoglobin change when oxygen binds?

  The size of the central cavity changes, affecting binding affinity
• What stabilizes the T state of hemoglobin in red blood cells?

  Something stabilizes the T state, leading to lower affinity for oxygen
• What is the role of 2,3-bisphosphoglycerate (2,3-BPG) in hemoglobin function?

  2,3-BPG binds in the central cavity and stabilizes the T state
• How does fetal hemoglobin differ from adult hemoglobin in terms of structure?

  Fetal hemoglobin is α₂γ₂ instead of α₂β₂
• Why does fetal hemoglobin have a higher affinity for oxygen than adult hemoglobin?

  Fetal hemoglobin has reduced affinity for BPG, stabilizing the R state
• What is the Bohr effect in relation to hemoglobin function?

  The Bohr effect describes how increased H⁺ and CO₂ levels lead to more oxygen release
• How does CO₂ affect hemoglobin's affinity for oxygen?

  CO₂ lowers the affinity of hemoglobin for oxygen
• What are the key messages regarding oxygen binding in hemoglobin and myoglobin?

  • Simple ligand binding gives a hyperbolic binding curve
  • Cooperative binding gives a sigmoidal shape, resulting in more oxygen bound in lungs and more released in metabolising tissues
  • Two models for cooperative binding exist, but reality is likely a mix of both
  • Allosteric effectors can influence affinity without binding to heme