PROTEINS ATA

• Proteins


  Covalently linked polymers of amino acids
• Amino acids


  Linked via peptide bond (formed upon removal of a water molecule)
• Protein synthesis


  Synthesized in the liver & secreted by the hepatocyte into the circulation EXCEPT immunoglobulins (plasma cells)
• Proteins


  Provide 12 – 20% of the total daily body energy requirement
• Proteins


  Compose 50 – 70% of the cell's dry weight
• Primary structure


  • Sequence of the amino acids in the polypeptide chain
• Secondary structure


  • Arises from the interaction among the different segments of a polypeptide chain
• Secondary structure types

  • Alpha-helix
  • Beta-pleated sheets
  • Random coils
• Tertiary structure


  • Actual 3-dimensional structure or folding pattern of the protein
• Quaternary structure


  • Association of several polypeptide chains into larger "oligomeric" aggregate unit
• Quaternary structure examples


  • Dimers
  • Trimers
  • Tetramers
• Protein classification


  • Simple
  • Conjugated
• Simple proteins


  Contain peptide chains that on hydrolysis yield only amino acids
• Simple protein types

  • Globular
  • Fibrous
• Conjugated proteins

  Protein (apoprotein) + nonprotein (prosthetic group)
• Prosthetic groups

  • Lipid (lipoprotein)
  • Carbohydrate (glycoprotein)
  • Metals (metalloprotein)
• Protein functions

  • Repair body tissues
  • Important in blood coagulation and immunologic function
  • Transport of metabolic substances
  • Maintenance of osmotic pressure
  • Maintenance of blood pH (buffers)
  • Biocatalysts
• Protein metabolism stages


  • Dietary Intake
  • Absorption
  • Production
  • Storage
  • Destruction
• Pre-albumin (Transthyretin)


  Migrates ahead of albumin, rich in tryptophan and contain 0.5% carbohydrate, serves as transport protein for T3, T4 and retinol (Vit. A)
• Albumin


  Largest plasma protein fraction (52-62%), synthesized in the liver at a rate that is dependent on protein intake, serves as circulating reservoir of amino acids, regulator of osmotic pressure, transport protein because of ease of binding with blood components, a "negative acute phase reactant"
• Reference values for albumin: 3.5 – 5.0 g/dL (35 – 50 g/L)
• Increased albumin (Hyperalbuminemia)


  Hemoconcentration, dehydration, excessive albumin infusion
• Decreased albumin (Hypoalbuminemia)


  Decreased synthesis (liver impairment), malabsorption or malnutrition, nephrotic syndrome (renal loss), severe burns
• Globulins


  Heterogenous complex mixture of protein molecules (α1, α2, β and γ fractions)
• Normal A/G ratio

  1.3 – 3 : 1
• Low A/G ratio


  Liver diseases, infectious diseases, multiple myeloma, nephritis
• Alpha 1 globulins


  α-1-antitrypsin, α-1-fetoprotein, α-1-Acid Glycoprotein (orosomucoid), α-1-Antichromotrypsin
• α-1-antitrypsin


  An acute phase reactant, neutralize trypsin-like enzymes, major inhibitor of protease activity
• α-1-fetoprotein


  Synthesized initially by the fetal yolk sac & then the parenchymal cells of the liver, used as a tumor marker (hepatic & gonadal CA), screening test for any fetal conditions
• α-1-Acid Glycoprotein (orosomucoid)


  Contains high percentage of CHO and sialic acid, synthesized both by the liver & by granulocytes and monocytes, inhibits the phagocytic activity of neutrophils & inhibits platelet aggregation, may inactivate progesterone
• α-1-Antichromotrypsin


  A member of the serine proteinase inhibitor (serpin) family, produced in the liver, an acute phase protein, it inhibits the activity of enzymes cathepsin G, pancreatic elastase, mast cell chymase, and chymotrypsin by cleaving them into different shapes
• Alpha 2 globulins


  Haptoglobin, Ceruloplasmin, α-2-Macroglobulin
• Haptoglobin


  An acute phase reactant, synthesized in the hepatocytes & cells of the RES, binds free hemoglobin by its α- chain
• Ceruloplasmin


  Copper-containing protein BUT does NOT transport copper, serves as an antioxidant to prevent lipid peroxidation & cellular damage
• α-2-Macroglobulin


  Largest major non-immunoglobulin protein in plasma, found principally in the intravascular spaces, inhibits proteases such as trypsin, pepsin and plasmin
• Beta globulins


  Transferrin (Siderophilin), β2-Microglobulin
• Transferrin (Siderophilin)


  Major component of the β2-globulin fraction, a glycoprotein synthesized in the liver, transports oxidized iron (Fe+3)to its storage sites, prevents loss of iron through the kidney
• β2-Microglobulin


  Light chain component of the major human leukocyte antigen (HLA), found on the surface of most nucleated cells, present in high concentration on lymphocytes, filtered by the renal glomerulus but reabsorbed
• Gamma-globulins

  Increased in chronic inflammation, cirrhosis or viral hepatitis, collagen diseases, paraproteins (monoclonal bands, gammopathies), Decreased in congenital or acquired immunodeficiency
• Immunoglobulins


  Synthesized in the plasma cells, not produced to any extent by the neonate