Hemoglobin - The Exchange Between O2 and CO2

Introduction

• hemoglobin is the powerhouse for bringing oxygen to cells that need it and removing carbon dioxide waste from those cells
• there are around 270 million hemoglobin protein molecules in a single Red Blood Cell (RBC)
• there are around 20 to 30 trillion RBCs in the human body

Hemoglobin (Hb)

• is a protein, that has 4 hemes
• each heme binds to either one:
  • H⁺ - proton
  • CO2 - carbon dioxide
  • O2 - oxygen

CO2 and O2 Exchange - Between RBC and Lungs

• HbO2 (Oxyhemoglobin) - the presence of abundant O2 binds to hemoglobin, thus creating HbO2
• O2 dissolved in plasma

CO2 and O2 Exchange - Between RBC and Cells That need O2

• reasons for O2 delivery:

  • low partial pressure of O2 and high partial pressure of CO2 cause diffusion to homoeostasis
  • H⁺ compete with O2 for Hb
  • CO2 compete with O2 for Hb

• steps for O2 delivery:

  • cells always makes CO2, the process is called cellular respiration
  • CO2 diffuses into capillaries
  • CO2 diffuses into RBC
  • H⁺ compete with O2 for Hb
    • with the presence of H2O in RBC an enzyme called carbonic anhydrase combines H2O and CO2 into a molecule carbonic acid
      CO2 + H2O → H2CO3
• • • since carbonic acid is an acid it will kick off a proton 
      H2CO3 ↔ HCO3⁻ + H⁺
• • • the proton binds to oxyhemoglobin and boots off the O2
      H⁺ + HbO2 ↔ H⁺Hb + O2
• • CO2 compete with O2 for Hb
    • CO2 binds to oxyhemoglobin and boots off the O2
      CO2 + HbO2 ↔ Hb-COO⁻ + H⁺ + O2
• • excess O2 diffuses out of RBC to cells that need it