TAILIEUCHUNG - Chapter 099. Disorders of Hemoglobin

Hemoglobin is critical for normal oxygen delivery to tissues; it is also present in erythrocytes in such high concentrations that it can alter red cell shape, deformability, and viscosity. Hemoglobinopathies are disorders affecting the structure, function, or production of hemoglobin. These conditions are usually inherited and range in severity from asymptomatic laboratory abnormalities to death in utero. Different forms may present as hemolytic anemia, erythrocytosis, cyanosis, or vasoocclusive stigmata. . | Chapter 099. Disorders of Hemoglobin Hemoglobin is critical for normal oxygen delivery to tissues it is also present in erythrocytes in such high concentrations that it can alter red cell shape deformability and viscosity. Hemoglobinopathies are disorders affecting the structure function or production of hemoglobin. These conditions are usually inherited and range in severity from asymptomatic laboratory abnormalities to death in utero. Different forms may present as hemolytic anemia erythrocytosis cyanosis or vasoocclusive stigmata. Hemoglobin Structure Different hemoglobins are produced during embryonic fetal and adult life Fig. 99-1 . Each consists of a tetramer of globin polypeptide chains a pair of a-like chains 141 amino acids long and a pair of p-like chains 146 amino acids long. The major adult hemoglobin HbA has the structure a2p2. HbF a2p2 predominates during most of gestation and HbA2 a2ỗ2 is minor adult hemoglobin. Embryonic hemoglobins need not be considered here. Figure 99-1 Cftnjm som s Hemogíũỉxnis F A A figure F ud Aflj Kltpiir CL Èr Hiuiír SLụ L jnflo 0t_ Jamaica Jl Lũjc lí J GỈ Ĩr-ĩiỉ tt 17th Lditicn trttp 4s ĩrvradi Copv j9ht iiTht M 5r4w-Hi l Ccmppnui Int All nshti m re d BenhHot .Com The globin genes. The a-like genes a s are encoded on chromosome 16 the p-like genes p y õ s are encoded on chromosome 11. The s and s genes encode embryonic globins. Each globin chain enfolds a single heme moiety consisting of a protoporphyrin IX ring complexed with a single iron atom in the ferrous state Fe2 . Each heme moiety can bind a single oxygen molecule a molecule of hemoglobin can transport up to four oxygen molecules. The amino acid sequences of the various globins are highly homologous to one another. Each has a highly helical secondary structure. Their globular tertiary structures can cause the exterior surfaces to be rich in polar hydrophilic amino acids that enhance solubility and the interior to be lined with nonpolar groups forming

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