Haemoglobin BY: MUHAMMAD RADWAN WISSAM MUHAMMAD

Transcription

1 Haemoglobin BY: MUHAMMAD RADWAN WISSAM MUHAMMAD

2 Introduction is the iron-containing oxygen transport metalloprotein in the red blood cells Hemoglobin in the blood carries oxygen from the respiratory organs (lungs) to the rest of the body (i.e. the tissues) where it releases the oxygen to burn nutrients to provide energy to power the functions of the organism in the process called metabolism. Each red cell has 640 million molecules of Hb

3 Introduction Haemoglobin (Hb), protein constituting 1/3 of the red blood cells Synthesis begins in proerythroblast Two parts 65% at erythroblast stage 35% at reticulocyte stage Haem Globin

4 Functions of Haemoglobin Oxygen delivery to the tissues Reaction of Hb & oxygen: Hb4 + 2O2 Hb4O4 Normal Hb Concentration in Blood: The averge normal Hb content of 16 g/dl in males and 14 g/dl in females Where each one gram of Hb bind with 1.34 ml of O2 and whole blood in healthy adults contains 15g of Hb per dl of blood Therefore O2 capacity of blood = 1.34 ml of O2 x 15gHb of blood = 20.1 ml o2 combine with Hb /dl

5 Structure of Hemoglobin : The hemoglobin molecule consists of 4 protein chains and 4 heme groups. Each protein called globin is bound to one heme Structure of heme : heme is chemical structure made up of a porphyrin ring with an iron atom inserted in the center.it is red pigment molecule containing one iron atom.the porphyrin is made up of pyrrole ring. Synthesis of heme takes place in mitochondria

6 Structure of globin The globin portion of the Hb is a protein (simple polypeptide chains made up of amino acids) There are two paires of polypeptides in each molecule, two of the subunits contin one type of polypeptides the other two contain another type of polypeptides : Alpha chain contain 141 amino acid residues. Beta chain contain 146 amino acid residues. Delta chain contain 146 amino acid residues but differ from beta chain by 10 amino acid residues Gamma chain also contain 146 amino acid residues differ from beta chain by 39 amino acid residues Synthysis of globin takes place in polyribosomes

7 Types of adult hemoglobin 3 6 % HBA: the major hemoglobin in humans HBA2: first appears 12 weeks after birth- a minor component of normal adult HB HBF: normally synthesized only during fetal development HBA1C : has glucose residues attached to b-globin chains increased amounts in DM

8 Hemoglobin A1c (HBA1c) Some of hemoglobin A is glycosylated Extent of glycosylation depends on the plasma concentration of a particular hexose (as glucose). The most abundant form of glycosylated hemoglobin is HBA1c which has a glucose residues attached to b-globin chains in hemoglobin RBCs. Increased amounts of HBA1c are found in RBCs of patients with diabetes mellitus (DM). HbA1c could be used as a monitor for the control of the blood glucose level during the last 2 months for diabetic patients

9 Wisssam Muhammad Hemoglobinopathies

10 Hemoglobinopathies Hemoglobinopathies are members of a family of genetic disorders caused by: 1- Production of a structurally abnormal hemoglobin molecule (Qualitative hemoglobinopathies) Or: 2- Synthesis of insufficient quantities of normal hemoglobin (Quantitative hemoglobinopathies) Or: 3- both (rare).

11 Mutations in hemoglobin (hemoglobinopathies) 1- Sickle cell anemia (Hb S disease): It is a genetic disorder of blood caused by mutation in β-globin chain resulting in the formation of Hb S. The mutation occurs in 6th position of β-chain where glutamic acid is replaced by valine (non polar). Valine residues aggregate together by hydrophobic interactions leading to precipitation of Hb within RBCs. RBCs assume sickle-shaped leading to fragility of their walls and high rate of hemolysis.

12 Patients may be : Heterozygotes (HbAS): There are two copies of the gene that synthesize β globin chain. In Hb AS, mutation occurs only in one copy of the gene so patients have some normal Hb A. These patients have sickle cell trait with no clinical symptoms and can have normal life span. Homozygotes (Hb SS): mutation occurs in both copies of gene that synthesize β-globin chain with apparent anemia and its symptoms

13 2- Hb C disease: Like HbS, Hb C is a mutant Hb in which glutamic acid in 6th position of β-chain is replaced by lysine. RBCs will be large oblong and hexagonal. The heterozygous form (Hb AC) is asymptomatic. The homozygous form (Hb CC) causes anemia, tissue anoxia and severe pain.

14 Thalassemia 3- Thalassemia: A group of genetic diseases in which a defect occur in the rate of synthesis of one or more of Hb chains, but the chains are structurally normal. This due to defect or absence of one or more of genes responsible for synthesis of α or β chains (see Fig.) leading to premature death of RBCs.

15 Types of thalassemia β -thalassemia: When synthesis of β chains is decreased or absent. There are two copies of the gene responsible for synthesis of β chains. Individuals with β globin gene defects have either : β -thalassemia minor (β thalassemia trait) : when the synthesis of only one β globin gene is defective or absent. Those individuals make some β chains and usually not need specific treatment. β -thalassemia major (Cooley anemia): if both genes are defective. - Babies will be severely anemic during the first or second year of life and so require regular blood transfusion. Bone marrow replacement is more safe treatment (why?).

16 Genes responsible for synthesis of Hb molecule (α and β globin chains)

17 a-thalassemia in which synthesis of α globin chain is defective or absent. There are four copies of gene responsible for synthesis of α globin chains so patients may have: i - Silent carrier of α-thalassemia with no symptoms: if one copy of the genes is absent ii- α-thalassemia trait: if two copies of genes are absent iii- Hb H disease: if 3 copies of genes are absent, with mild to moderate anemia. The produced Hb will be β 4 which is called Hb H. Oxygen delivery to tissues will be blocked because Hb H (β 4 ) which bind O 2 but does not deliver it to tissues. iv- Hydrops fetalis: when all 4 copies of α globin genes are absent. It causes fetal death (babies with this disorder usually die before or shortly after birth) because α globin chains are required for synthesis of Hb F.

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19 The inheritance of alpha thalassemia is complex because each parent potentially passes two of their four alpha globin genes to the offspring

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