MT303A LEC - (WEEK 3) HEMOGLOBIN SYNTHESIS-1.pdf

MT303A LEC WEEK 3: HEMOGLOBIN SYNTHESIS (TRANSCRIPT) BSMLS HEMOGLOBIN HEMOGLOBIN ASSEMBLY...

MT303A LEC WEEK 3: HEMOGLOBIN SYNTHESIS (TRANSCRIPT) BSMLS HEMOGLOBIN HEMOGLOBIN ASSEMBLY  Inheritance - Normal adult  After their release from ribosomes, each globin chain binds to a hemoglobin A is inherited in heme molecule and they pair off simple mendelian fashion.  An α chain and a non-α chain combine to form heterodimers The genotype for this o Two heterodimers spontaneously combine to form phenotype is A/A tetramers  Composition - Consists of 4 o The tetrameric α1β2 and α2β1 bonds also contribute to the heme groups and four stability of the structure polypeptide chains with a o This completes the hemoglobin molecule total of 574 amino acids  Function - Transport of oxygen to the tissues HEME STRUCTURE  Heme consists of a ring of carbon, hydrogen, and nitrogen atoms called protoporphyrin IX HEMOGLOBIN REGULATION with an atom of divalent ferrous  Hemoglobin synthesis is normally stimulated by tissue hypoxia iron (Fe2+) attached  Hypoxia - Causes the kidneys to produce increased erythropoietin,  Each of the 4 heme groups is which stimulates the production of hemoglobin and RBCs positioned in a pocket of the o Men - 14-18g/dL (140-180g/L) polypeptide chain near the o Women - 12-15g/dL (120-150g/L) surface of the hemoglobin o Newborns – 16.5-21.5g/dL (165-215g/L) molecule ROLE OF 2,3-DIPHOSPHOGLYCERATE o Each heme molecule combines reversibly with one oxygen  Oxygen affinity of the hemoglobin molecule is associated with the molecule spatial rearrangement of the molecule and is regulated by the o Owing to its double bonds, heme renders blood red concentration of phosphates, particularly 2,3-DPG in the GLOBIN STRUCTURE erythrocytes  4 globin chains comprising OXYGEN DISSOCIATION CURVE each hemoglobin  Affinity of hemoglobin for oxygen depends on the partial pressure molecule consist of 2 of oxygen (PO2), often defined in terms of the amount of oxygen identical pairs of unlike needed to saturate 50% of hemoglobin, called the P50 value polypeptide chains, 141 to  The curve is sigmoidal, which indicates low hemoglobin affinity for 146 amino acids each oxygen at low oxygen tension and high affinity for oxygen at high  Variations in amino acid oxygen tension sequences give rise to  Shifts of the curve to the left or right occur if there are changes in different types of the pH of the blood polypeptide chains o This shift in the curve as a result of pH is termed the Bohr  Each chain is designated by a Greek letter effect HEMOGLOBIN SYNTHESIS 1. HEME SYNTHESIS HEMOGLOBIN VARIANTS 1. METHEMOGLOBIN 2. GLOBIN SYNTHESIS  Form of hemoglobin that contains iron in the oxidized or ferric state  6 structural genes control the synthesis of the six globin chains (Fe3+)  The production of globin chains takes place in RBC precursors from  Methemoglobin is brownish to bluish and does not revert to red the pronormoblast through the circulating polychromatic upon oxygen exposure (polychromatophilic) erythrocyte, but not in the mature RBC  Ferric iron cannot bind oxygen, but when one or more ferric ions  Globin proteins arise via transcription of the genetic code to are present the conformation of the molecule changes, and the messenger ribonucleic acid (mRNA) and translation of mRNA to the oxygen affinity of the remaining heme groups increases globin polypeptide chain 2. SULFHEMOGLOBIN  Formed by the irreversible oxidation of hemoglobin by sulfonamides, phenacetin, acetanilide, or phenazopyridine  Created in vitro by the addition of hydrogen sulfide to hemoglobin and has a greenish pigment  Causes the blood to be colored mauve-lavender 3. CARBOXYHEMOGLOBIN  Formed from the combination of carbon monoxide with heme iron o Carbon monoxide has been termed the silent killer because it is an odorless and colorless gas, and victims may quickly become hypoxic  Carboxyhemoglobin may be detected by spectral absorption instruments at 541 nm o Gives blood a cherry-red color, which is also imparted to the skin of victims o Hyperbaric oxygen therapy has been used for treatment HEMOGLOBIN DETERMINATION 1. Colorimetric Method I. Visual II. Photoelectric 2. CuSO4 (Copper Sulfate) Method BACHELOR OF SCIENCE IN MEDICAL LABORATORY SCIENCE SXIA  MT303A LEC WEEK 3: HEMOGLOBIN SYNTHESIS (TRANSCRIPT) BSMLS 3. Gasometric Method 6. HEMOGLOBIN ELECTROPHORESIS 4. Chemical Method  Principle - Separation of Hemoglobin molecules in electric field due 5. Electrophoresis - Automated technique to determine haemoglobin to difference in total molecular charge content in the blood  Gel Electrophoresis 1. COLORIMETRIC METHOD (VISUAL) o Medium - Agarose, cellulose acetate I. Tallquist Method o Modern Use - Agarose gel  Capillary puncture I. Alkaline Hemoglobin Electrophoresis  Toward anode  8.4-8.6 II. Acid Hemoglobin Electrophoresis  6-6.2 7. OTHER METHODS OF HEMOGLOBIN DETERMINATION I. High Performance Liquid Chromatography (HPLC)  Separate in cation  Thalassemia II. Dare’s Method  Monitor diabetic patients  HbA1C II. Capillary Electrophoresis  Similar to agarose III. Isoelectric Focusing (IEF)  Confirmatory technique III. Acid Hematin Method  Conversion of hemoglobin to acid hematin  EDTA  Reagents - 0.01 N HCl + Distilled water 2. COLORIMETRIC METHOD (PHOTOELECTRIC) I. Oxyhemoglobin Method II. Cyanmethemoglobin Method  Hemoglobin  Methemoglobin  Cyanmethemoglobin  Preferred hgb determination by CLSI  Potassium ferry cyanide  Drabkin’s reagent  Methemoglobin to cyanmethemoglobin 3. COPPER SULFATE METHOD  Ginagawa sa blood donation  Ability to maintain density  Specific gravity method  Drop of blood directly proportional to hgb  1.053  Sink - Higher than hgb  Float - Lower 4. GASOMETRIC METHOD  Principle - Indirect measure of Hgb based from the fact that one molecule of 02 binds to each iron atom 5. CHEMICAL METHOD  Hemoglobin Solubility Test  Decrease solubility of the oxygenated haemoglobin  Salt solution, sodium hydrosulphate, saponin  Positive - Turbidity BACHELOR OF SCIENCE IN MEDICAL LABORATORY SCIENCE SXIA