Lecture 13 Hemoglobin New

Lecture 13 Hemoglobin New - Lecture 13 Hemoglobin New

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Lecture 8: Example of biological functions of protein : Transport of oxygen and carbon dioxide by hemoglobin
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Oxygen has a low solubility in blood (0.1 mM). Whole blood, which contains 150 g Hb/L, can carry up to 10 mM oxygen gas. Invertebrate can have alternative proteins for oxygen binding, including hemocyanin, which contains Cu and hemerythrin, a non-heme protein. Among the normal Hb-A (adult hemoglobin), in about 2.5% of Hb-A, the beta-chains are replaced and the hemoglobin is called Hb-A 2 (2 alpha chains and 2 delta chains). The 97.5% of Hb-A is called Hb-A l (2 alpha and 2 beta chains) which constitute the normal hemoglobin. The Hb-F consists of 2 alpha and 2 gamma chains.
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Red blood cells are important in the process of respiration. Gases involved in respiration are carried around the body through these cells. Oxygen readily combines with haemoglobin to form oxy-haemoglobin in the lungs where there is high concentration of oxygen. However, oxy- haemoglobin is an unstable compound and will break down to release oxygen when there is low concentration of oxygen in the surroundings. Hence there will be an even distribution of oxygen to all parts of the body. Red blood cells also carry part of the carbon dioxide waste from the cells through most is transmitted through plasma as soluble carbonates.
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Why hemoglobin is so effective in transporting oxygen? Hemoglobin is very effective in transporting oxygen: the quaternary structure of hemoglobin leads to physiologically important allosteric interactions between the subunits, a property lacking in monomeric myoglobin. The curve of oxygen binding to hemoglobin is sigmoidal typical of allosteric proteins in which the substrate, in this case oxygen, is a positive homotropic effector. Why?
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The Fe ion is coordinated to 4 N's on the 4 pyrrole rings, The 5th ligand is a supplied by proximal His (the 8th amino acid on helix F) of the protein . The 6 ligand is missing. and the geometry of the complex is square pyramidal with the Fe above the plane of the heme ring. A distal His (E7) is on the opposite side of the heme ring, but too far to coordinate with the Fe. When oxygen binds, it occupies the 6th coordination site (Interaction stabilize by H bonding with distal E7 His) and pulls the Fe into the plane of the ring, leading to octahedral geometry. CO, NO, and H 2 S also bind to the 6th site, but with higher affinity than oxygen, which can lead to CO poisoning . When the heme Fe binds oxygen it is pulled into the plan of the heme
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Lecture 13 Hemoglobin New - Lecture 13 Hemoglobin New

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