Hemoglobin Structure Textbook Notes

‭Hemoglobin structure‬ ‭ uman hemoglobins are tetrameric, 4 polypeptide chains of globins identical in pairs and each‬ H ‭globin chain carries a heme which is the site oxygen binding agent. The type of globin chain‬ ‭determines the type of globin. The majority of hemoglobin in humans is 2 ubiquitous alpha chains:‬ ‭alpha 2 beta 2 is type A hemoglobin. Alpha 2 delta 2 is hemoglobin A2 which ist minority.‬ ‭ etal hemoglobin is made up of two alpha chains and two gamma chains, this fetal hemoglobin is‬ F ‭sought to highlight when there is childbirth: a woman who is rhesus negative and who gives birth to‬ ‭a rhesus positive child.‬ I‭ f there is passage of fetal hemoglobin to the mother, this must be known because there is a‬ ‭possibility of alloimmunization, that is to say that the mother synthesizes antibodies directed against‬ ‭rhesus and during a next pregnancy if the 2th child is again rhesus positive, the IgG‬ ‭immunoglobulins pass the barrier and during the second pregnancy these immunoglobulins will‬ ‭destroy the red blood cells which are rhesus positive.‬ ‭ n the first day of intrauterine life there is no ubiquitous chain but chainsteta and‬ O ‭epsilon.‬ ‭•‬ ‭primary structure‬‭:the alpha chain has 141 AA, 146‬‭for the beta.‬ ‭•‬ ‭secondary structure‬‭:amino acids are spirally wound‬‭around an axis so constitutes an alpha‬ ‭helix.‬ ‭•‬ ‭tertiary structure:‬‭it is the application of this alpha‬‭spiral which allows the constitution of‬ ‭an area where we will have the active site:heme for oxygen fixation.‬ ‭•‬ ‭quaternary structure‬‭:Association of the 4 globin molecules.‬‭There are bonds‬ ‭•‬ ‭between the alpha 1 and beta 1 heterodimers which are numerous and narrow while between‬ ‭the alpha 1 and beta 2 heterodimers we will have fewer, less rigid bonds which will allow changes‬ ‭in spatial conformation including the sliding of globin chains one by rapport to others to facilitate‬ ‭access of oxygen to the heme site.‬ ‭ he oxygenated form is called relaxed and the constrained form which has a low affinity for‬ T ‭oxygen. The heme that attaches to each globin molecule is a heterocycle tetrapyrolic, the pyrrole‬ ‭nuclei are linked together by radicals and iron in position central is connected to the pyrrole nucleus‬ ‭via a nitrogen molecule. There are two left free valences:one for the globin chain and one for‬ ‭oxygen.‬ ‭ Origin of erythrocytes:‬‭The elements come from the‬‭hematopoietic bone marrow During the first‬ ✪ ‭days of intravascular life they still contain rRNA which can be highlighted by brilliant cresyl blue‬ ‭or methylene blue which are po dyesTo highlight the fine filaments inside the red blood cells, these‬ ‭elements which contain rRNA are called “ reticulocytes'' which represent 1% of red blood cells.‬ ‭ Their concentration is 20 to 120 giga /L. Their interest: Following a hemorrhage he there will be‬ ✪ ‭an adaptation of the volumes and the patient will adapt by synthesizing many more red blood cells,‬ ‭if the number of reticulocytes increases it means that there is a good adaptation, if there is no‬ ‭increase there is a problem at neither calf hematopoietic bone marrow.‬ ‭ After 24 hours of life, these rRNAs are no longer highlighted.‬‭Properties of erythrocytes‬‭:great‬ ✪ ‭plasticity since the red blood cells can pass through the capillaries smaller than their sizes, the GRs‬ ‭aret a tendency towards aggregation, can form rolls and this is favored by high concentrations of‬ ‭fibrinogen. The GR also tends to agglutinate in the presence of antibodies, agglutination finalized‬ ‭by a cell lysis of RBCs. This property is used to determine blood groups and in certain pathologies‬ ‭there may be autoantibodies directed against certain parts of the RBC. and at this time it is an‬ ‭agglutination which tends to intravascular destruction.‬ ‭✪Red blood cell function‬‭:The transport of oxygen and‬‭carbon dioxide.‬ ‭ Destiny :‬‭The erythrocyte has a stock of protein that‬‭it cannot renew because there is no nucleus,‬ ✪ ‭more ribosomes. The derivative is therefore limited to 120 days. During this period of life the‬ ‭capacities of the red blood cells decrease, that is to say the capacity for deformation which will‬ ‭decrease, the affinity for oxygen will also decrease. After 120 days these elements will be destroyed‬ ‭by macrophages mainly in the hematopoietic bone marrow and in a minority in the spleen. The iron‬ ‭will be recycled.‬