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SYNTHESIS OF HEMOGLOBIN HEMOGLOBIN Conjugated protein: heme + globin Starts in proerythroblast stage. Appears in intermediate normoblastic stage. Continues until stage of reticulocyte. Heme portion is synthesized in mitochondria. Globin, protein part, is synthesized in ribosomes. SYNTHESIS OF HEME: Step1: inside mitochondria. Acetic acid succinyl CoA 2 succinyl CoA+ 2 glycine ALA synthetase-> δALA Step 2: ALA goes to cytoplasm. ALA+ ALA ALA hydrase porphobilinogen. Porphobilinogen uroporphobilinogen I synthetase-- uroporphobilinogenI. Uroporphobilinogen I porphobilinogenIII cosynthase-- uroporphobilinohen III uroporphobilinogenIII uroporphobilinogen decarboxylase coproporphyrinogenIII Step 3: transport back to mitochondria Corpoporphyrinogen III corpoporphyrinogen oxidase - protoporphyrinogenIX Protoporphyrinogen IX protoporphyrinogen oxidase- protoporphyrin IX Protoporphyrin IX + iron- heme. STEPS Acetic acid succinyl CoA 2 succinyl CoA+ 2 glycine Pyrrole 4 Pyrrole Protoporphyrin IX Protoporphyrin IX + Ferrous heme Heme + globin hemoglobin chain TYPES OF HB Hb A 2 alpha + 2 beta Hb A2 2 alpha + 2 delta Hb F 2 alpha + 2 gamma Gower I Hb 2 zeta + 2 epsilon Gower II Hb 2 alpha + 2 epsilon FORMATION OF GLOBIN Ribosomes produce polypeptide chains. 4 types: alpha, beta, gama and delta. Different on basis of amino acid sequence. 2 pairs of chains form one globin molecule. Each chain is made of 141-146 amino acids. Hb-A = 2 alpha, 2 Beta Hb-F = 2 alpha, 2 gama. CONFIGURATION I polypeptide chain= 1 heme molecule After completion 1 hemoglobin molecule has 4 polypeptide chain and 4 heme molecules. DESTRUCTION OF HEMOGLOBIN. RBCs are destroyed after 120 days. Sites of destruction: Reticuloendothelial system Spleen Then Hb is released into plasma. Hb degradation in reticuloendothelial system. Split into heme and globin. Globin utilized in the resynthesis of Hb. Heme degradation= iron+ porphyrin. Iron is stored in body as ferritin and hemosiderin. They are reutilized for synthesis of new Hb. Porphysin is converted into green pigment= biliverdin. In humans: biliverdin is converted into bilirubin. Biliverdin+ bilirubin= bile pigments IRON METABOLISM: Iron is essential mineral. Important component of protein. Required for Hb and myoglobin formation. Involved in oxygen transport. So required in human body for oxygen transport. Required for the synthesis of: Cytochrome. Cytochrome oxidase, Peroxidase, Catalase. NORMAL VALUES AND DISTRIBUTION OF IRON IN BODY: Total iron in body: 4g. In Hb: 65% - 68%. Myoglobin: 4%. Intracellular oxidative heme compound: 1% In plasma as transferrin stored: 0.1% Stored in reticuloendothelial system and liver :25%-30%. Bound with transerrin in plasma- 0.1% Stored in liver (ferritin and hemosiderin) DIETARY IRON: Available in heme and non heme forms. Heme: Present in fish, meat and chicken. Absorbed easily from intestine. Non heme: Vegetables, grains and cereals. Not absorbed easily. ABSORPTION OF IRON: Mainly from small intestine. Bile is essentail for iron absorption. Enterocytes -> pinocytosis -> digested by lysosomes From enterocytes to blood by a protein called ferroportin. Present in ferric form. Converted to ferrous and absorbed in blood. Ferrous iron -> HCL -> soluble. Ferrous acted upon by ferric reductase -> ferric iron. TRANSPORT OF IRON: In blood, ferrous combines with beta globulin called apotransferrin. Iron + apotransferrin -> transferrin. Iron binds loosely with globin and can be released easily at any region of body. STORAGE OF IRON: Excess Fe combines with apoferritin to form ferritin which is stored esp. In liver cells and Reticuloendithelial cells. Small amounts in other cells. Cytoplasm -> Large amount: stored as ferritin. Small amount: as hemosidrin when apoferritin pool is saturated. DAILY LOSS OF IRON: 1g Hb -> 3.34 mg of iron. 100 ml blood -> 15gm Hb and 50 mg iron. Males: 1mg iron excreted through faeces. Females: 50 ml blood loss -> 25 mg iron. Loss of blood in haemorrhage. Loss of blood in donation: 450ml blood -> 225mg of iron. REGULATION OF TOTAL IRON IN BODY: Absorption = excretion. Increase iron in body = decrease absorption. No apotransferrin formation in liver. Reduction in release of iron from transferrin. Transferrin is saturated. Further absorption is prevented.