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Second lecture

Second lecture. Plasma proteins. 2-Globulins : (2.7%) a globulins and b globulins: Transport lipids and fat soluble vitamins. g globulins: Antibodies. . Plasma proteins. 2-Globulins : (2.7%). Synthesis In lymphocytes (T and B)

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Second lecture

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  1. Second lecture

  2. Plasma proteins 2-Globulins: (2.7%) • a globulins and b globulins: • Transport lipids and fat soluble vitamins. • g globulins: • Antibodies.

  3. Plasma proteins 2-Globulins: (2.7%) • Synthesis • In lymphocytes (T and B) • Made in response to presence of antigen (“foreign” macromolecule, virus particle etc.) • Functions • Primary function is antigen binding (immune response) • Secondary function is complement binding (after antigen)

  4. Classes of Immunoglobulins • IgG: Microorganisms identification & engulfment. • IgE: Inhibits parasite invasion; involved in allergic reactions. • IgA: • Passive immunity provided by breast milk. • Agglutinates infectious agents in secretions outside the body. • Present in tears & mucous. • IgM: Microorganisms identification & engulfment.

  5. Plasma proteins 3-Fibrinogen: (0.3%) • Structure • MW 340 000 • Sequence of amino acids is known (3000) • 6 polypeptide chains, 2a (67,000), 2b (56,000), 2g (47,000) • Coagulation

  6. separation of plasma proteins • 1-Size Exclusion Chromatography (SEC) • Porous matrix (sephadex). • 2-Affinity chromatography • molecule attached to a column that specifically binds the protein of interest. • Coenzyme / enzyme • Antigen / Antibody • 3-SDS-PAGE (polyacrylamide gel electrophoresis) • Separates by size. • Proteins are complexed with SDS to give the same charge density.

  7. Zone Electrophoresis of Plasma Proteins + - globulins albumin g b a1 a2 6.0 5.6 5.1 4.7

  8. separation of plasma proteins • 4-Precipitation by salts: -Albumin is separated by full saturation with ammonium sulphate. -Globulins are precipitated by half saturation with ammonium sulphate. • 5-Ultra centrifugation: -Plasma proteins can be separated according to their different rates of sedimentations. -The sedimentation rate depends on weight, shape of the molecule & density of suspending medium.

  9. Functions of Plasma Proteins • Maintenance of: • Colloid osmotic pressure. • pH. • electrolyte balance. • Transport of: ions, fatty acids, steroids, hormones etc. • Albumin (fatty acids), ceruloplasmin (Cu2+), transferrin (Fe), lipoproteins (LDL, HDL).

  10. Functions of Plasma Proteins • Nutritional:source of amino acids for tissues. • Hemostasis:(coagulation proteins). • Prevention of thrombosis:(anticoagulant proteins). • Defense against infection:(antibodies, complement proteins).

  11. Synthesis of plasma proteins • All albumin, all fibrinogen and most of the globulins (50-80%) (alpha & beta) are formed in the liver. • Assembly time on ribosome ~ 1-2 min. • t0.5 in circulation - 19 days. • 14 g lost per day. • 0.4 mg synthesized per hour per g of liver. • The remaining part of globulins (gamma) are formed in the lymphoid tissues.

  12. Catabolism of plasma proteins • Plasma proteins circulate not only inside the vascular system but also across the capillary bed into the interstitial fluid and back into the plasma through lymphatic vessels. • Tissue macrophages take up albumin by pinocytosis. • Albumin is broken down within the lysosomes of tissue macrophages to amino acids.

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