Hemoglobin (Structure, Function, and Synthesis) PDF

Hemoglobin (structure)  normal adult haemoglobin A (Hb A).  consists of : - four polypeptide chains, α2 β2. - four haem groups.  Also, normal adult contains Hb F and Hb A2. Hemoglobin (structure)  protoporphyrin combines with iron in the ferrous (Fe2+)...

Hemoglobin (structure)  normal adult haemoglobin A (Hb A).  consists of : - four polypeptide chains, α2 β2. - four haem groups.  Also, normal adult contains Hb F and Hb A2. Hemoglobin (structure)  protoporphyrin combines with iron in the ferrous (Fe2+) state to form haem.  It absorbs visible light and colors heme deep red Hemoglobin (structure)  Globin in hemoglobin is spherical, tetrameric protein containing four heme prosthetic groups.  The structure has strong hydrophobic interactions between unlike subunits (α1β1 and α2β2).  The binding of O2 to a hemoglobin subunit cause structural conformational change.  Oxygen release is enhanced by the binding of 2,3-diphosphoglycerate (DPG), which stabilizes the quaternary structure of deoxyhemoglobin. Hemoglobin synthesis 1. Haem synthesis occurs in the mitochondria. 2. Vitamin B6 is a coenzyme for this reaction. 3. Iron (Fe) is supplied from circulating transferrin. 4. Globin chains are synthesized on ribosomes. 5. Protoporphyrin combines with ferrous (Fe2+) to form haem. 6. Four globin chains each with its own haem make up a haemoglobin molecule. Hemoglobin (function)  Carry O2 from the lungs to the tissues (at PO2).  Return blood with CO2 to the lungs.  When Fe(II) goes to Fe(III), oxidized, it produces methemoglobin which is brown.  Dissociation curve of hemoglobin O2 depend on: - 2,3‐DPG (2,3‐diphosphoglycerate) - H+ ions in RBC - CO2 in RBC - hemoglobin structure. Hemoglobin (Oxygen Dissociation Curves)  Curve shift right (O2 is given up easily):  High concentrations of 2,3‐DPG, H+ or CO2, and the presence of sickle hemoglobin (Hb S)  Curve shift left (O2 is given up less readily):  fetal hemoglobin (Hb F)  unable to bind 2,3‐DPG  hemoglobins associated with polycythaemia (abnormal)  carbon monoxide (CO) kills human because it disrupts the physiologic function of hemoglobin.  When a drug or toxic substance oxidizes hemoglobin, this will cause formation of methemoglobinaemia (Hb M) (abnormal hemoglobin). Bohr Effect  Higher pH (low [H+]) promotes tighter binding of oxygen to hemoglobin  and  Lower pH (higher [H+]) permits the easier release of oxygen from hemoglobin Bohr Effect HbO2 n Hx  O2  HbO2 n 1  xH   CO2  H2O  H  HCO3 - Hematocrit  It is defined as the volume percentage of red blood cells in a given sample of blood after centrifugation (HCT).  It is also referred as:  Packed Cell Volume (PCV)  or erythrocyte volume fraction (EVF) Hematocrit  Decrease in the number or size of RBCs will decreases the amount of space they occupy, resulting in a lower hematocrit.  Hematocrit test is carried out for detecting the presence and degree of anemia or polycythemia.  Hemoglobin estimation is less accurate, and RBC count far less accurate. Hematocrit  Microhematocrit tube is a capillary tube, 75mm in length and 1mm in diameter.  tube contains heparin (anticoagulant) and show a red ring at the end of it.  Normal ranges:  Males : 40 %–54 %  Females : 36 %–47 %  Newborns : 55-68 %.  viscosity of blood increases as the hematocrit increases.