1Chapt. 44Ch. 44 Biochemistry of ErythrocytesStudent Learning Outcomes:• Describe the structure/ function of blood cell types:• Erythrocytes, leukocytes, thrombocytes• Explain the metabolism of the red blood cell• Explain basics of hematopoiesis from bone marrow• Describe some errors of hemoglobin function, anemias, hemoglobin switching• Describe the structure/ function of blood group antigens (Ch. 30)Blood cellsTable 1 Blood cells (cells/mm3):• Erythrocytes 5.2 x 106mencarry oxygen 4.6 x 106women• Neutrophils 4300granules; phagocytic, O2burst kills• Lymphocytes 2700immune response, B- and T-cells, NK• Monocytes 500macrophages for bacteria, damage• Eosinophils 230granules destroy parasites (worms)• Basophils 40• granules hypersensitivity, allergichistamine, proteases, HematopoiesisFig. 15Hematopoiesis:• Stem cells in bone marrow (1/105)• Proliferate, differentiate, matureby growth factors, hormonessignal transduction paths• Myeloid, lymphoid lines• Leukemias: immature cellskeep proliferating;defined by cell typeAnemiaAnemias: hemoglobin concentration is low:• Normal Hb g/dL: men 13.5-17.5; women 11.5-15.5Anemias classified by red blood cell morphology:Rbc morphology functional deficit possible causeMicrocytic, impaired Hb thalassemia, lead,hypochromic synthesis iron deficiencyMacrocytic impaired DNA vit B12or folic acidnormochromic synthesis deficient, erythroleukemiaNormocytic red cell loss acute bleeding, normochromic sickle cell defects2Erythrocyte metabolismErythrocyte metabolism: Only glycolysis• ATP for Na+/K+, Ca2+• HMP shunt makes NADPHG6PD is 1stenzymeLifetime rbc by G6PD activity• 2,3-BPG modulates O2binding• Need Fe2+ Hb bind O2;If ROS made Fe3+, NADH can reduceFig. 1Heme synthesisHeme synthesis in erythrocyte precursor:• Heme = porphryn ring, coordinated to Fe• Complexed to proteins in hemoglobin, myoglobin and cytochromes; most common porphryn in body• 4 pyrrole rings with –CH- joining• Various side chains• Heme is red colorFig. 2Heme synthesisFig. 3Heme synthesis:Glycine, succinyl CoA formδ-Aminolevulinic acid (δδδδ-ALA) Each heme needs 8 of eachFinal step is Fe2+Heme regulates:inhibit 1stenzymerepress synthesisPorphyria diseases fromdefective enzymesintermediates accumulatephotosensitive, toxic productsHeme synthesisFig. 4Heme synthesis begins with δδδδ-ALA:• Decarboxylation by δ-ALA synthase• PLP is pyridoxal phosphate• Dehydratase joins 2 δ-ALA• 4 pyrroles form porphyrinogen3Sources of iron and hemeIron is essential from diet – 10-15 mg/day recommendedIron is not readily absorbed from many sourcesIron in meats is form of heme, readily absorbedNonheme iron of plants not as easily absorbed becauuse other compounds precipitate ironIron absorbed in ferrous state (Fe2+), oxidized by ferroxidase to Fe3+ for transportApotransferrin binds Fe3+ = TransferrinStored as ferritin in cellsHeme stimulates synthesis of globin proteins from ribosomesIron metabolismFig. 6RE = reticulo-endothelial systemIron metabolism:• Transferrin carries Fe3+ to cells; stored as ferritin• Transferrin taken up by R-mediated endocytosis• Hemosiderin stores excessDegradation of hemoglobinFigs. 7,8Heme is degraded to bilirubin:• Bilirubin is congugated to glucuronate (more soluble),excreted• Rbc only live ~120 days• Globin is degraded to amino acidsRed blood cellsErythrocyte cell membrane:• Red disc, pale center• Biconcave shape • Maximizes surface area• 140 um2vs. 98 um2 sphere• Deforms to enter tissues• Spleen destroys damagedred blood cellsFig. 94Cytoskeleton of erythrocyteFig. 10 general side view; inside cell view upErythrocyte cytoskeleton• provides shape, structure, permits stretch• 2-D lattice of proteins links to membrane proteins:• spectrin (α, β)• actin• ankyrin• band 4.1• membrane proteins:• glycophorin• band 3 protein•Mature rbc does not synthesizenew proteins• Gets lipids from circulating LDLAgents affect oxygen binding of hemoglobinFig. 11,12, 14Agents affect oxygen binding of hemoglobin:• 2, 3-BPG (glycolysis intermediate) binds between 4 subunits of Hb, lowers affinity for O2, releases O2to tissues• Proton (Bohr) effect: ↑H+lowers affinity of Hb for O2: • CO2can bind to Hb (not only bicarbonate)Effect of H+on oxygen binding to HbEffect of H+on oxygen binding to Hemoglobin:• Tissues: CO2released → carbonic acid, H+• H+bind Hb → release O2to tissues• Lungs reverse: O2binds H+Hb → release H+• H2CO3forms, releases CO2to exhaleFig. 13HematopoiesisFig. 15Hematopoiesis:• Stem cells in bone marrow• proliferate• differentiate• mature• myeloid vs. lymphoid• Stromal cells secretegrowth factors• Cytokines signal viamembrane receptors5Bone marrowBone marrow stromal cells secrete growth factorsHematopoietc stem cells respondHematopoiesis involves cytokine signalingFigs. 16; 11.15Growth factors signal through membrane receptors:• Ligand causes receptors to aggregate• Activates JAK (kinases) by phosphorylation (cytoplasmic RTK)• JAK phophorylates cytokine receptor on Tyr• Other signaling molecules bind, including STAT (signal transducer and activator of transcription) → nucleus transcription• Also RAS/Raf/MAP kinase activated • Overactive signal → cancer• Transient signal:SOCS silencesErythropoiesisFig. 17Erythropoiesis:Erythropoietin from kidney increases red blood cell proliferation (if low oxygen)• Reticulocytes still have ribosomes, mRNA to make HbMature in spleen, lose ribosomes• Make 1012rbc/day• Anemia if not appropriate diet• Iron, vitamin B12, folateHemoglobin genesHemoglobinopathies, hemoglobin switching:• Order of genes parallels development, controls• >700 mutant Hb (often base subsittution)• HbS sickle cell (Hb β Glu6Val)• HbC (Hb β Glu6Lys)Both ↑ malaria resistanceFig. 186ThalassemiasThalassemias: unequal production of α, β α, β α, β α, β of Hb:• need a:b 1:1• α has 2 genes each chromosome; β only 1• can have amino acid substitutions, promoter mutations, gene deletions, splice• Improper synthesis cause instability, or aggregation β + has some β; β0makes none• People offten survive if hereditary persistence of fetal hemoglobin: HPFH (α2γ2= HbF)• Treatments of β-thalassemia or sickle cell:increase Hb γ transcriptionVI. Hemoglobin switchingHemoglobin switching:• embryo blast synthesis yolk• fetus liver synthesis• adult bone