1 / 47

Chapter 6

Chapter 6. Protein. Functional Categories. Catalysts - enzymes Hydrolases - cleave compounds Isomerases - transfer atoms in a molecule Ligases (synthases) - join compounds Oxidoreductases - transfer electrons Transferases - move functional groups. Functional Categories. Messengers

cerise
Download Presentation

Chapter 6

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chapter 6 Protein 2009 Cengage-Wadsworth

  2. Functional Categories • Catalysts - enzymes • Hydrolases - cleave compounds • Isomerases - transfer atoms in a molecule • Ligases (synthases) - join compounds • Oxidoreductases - transfer electrons • Transferases - move functional groups 2009 Cengage-Wadsworth

  3. Functional Categories • Messengers • Hormones • Structural elements • Contractile proteins • Fibrous proteins • Globular proteins • Immunoprotectors • Immunoproteins (antibodies) 2009 Cengage-Wadsworth

  4. Functional Categories • Transporters • Albumin • Transthyretin (prealbumin) • Transferrin • Ceruloplasmin • Lipoproteins 2009 Cengage-Wadsworth

  5. Functional Categories • Buffers • Regulation of acid-base balance • Fluid balancers • Proteins attract water to blood • Other roles • Adhesion, signaling, receptors, storage • Conjugated proteins • Glycoproteins • Proteoglycans 2009 Cengage-Wadsworth

  6. Protein Structure & Organization • Primary structure • Sequence of covalent bonds among amino acids • Secondary structure • Hydrogen bonding • -helix • -conformation or -pleated sheet • Random coil 2009 Cengage-Wadsworth

  7. Protein Structure & Organization • Tertiary structure • Clustering of hydrophobic AAs toward center • Electrostatic (ionic) attraction • Strong covalent bonding between cysteine residues - disulfide bridges • Quaternary structure • Interactions between 2 or more polypeptide chains • Oligomers 2009 Cengage-Wadsworth

  8. Amino Acid Classification • Structure • Central C • At least 1 amino group (NH2) • At least 1 carboxy (acid) group (COOH) • Side chain (R group) • Makes AA unique 2009 Cengage-Wadsworth

  9. Amino Acid Classification • Net electrical charge • Zwitterions have none • Polarity • Polar or nonpolar • Determined by R group • Essentiality • Lysine, threonine & histidine totally indispensable 2009 Cengage-Wadsworth

  10. Sources of Protein • Exogenous sources • Animal products - except fats • Plant products - grains/grain products, legumes, vegetables • Endogenous proteins • Desquamated mucoasal cells • Digestive enzymes & glycoproteins 2009 Cengage-Wadsworth

  11. Digestion & Absorption • Protein digestion • Mouth & esophagus - none • Stomach • HCl denatures • Pepsin hydrolyzes peptide bonds 2009 Cengage-Wadsworth

  12. Digestion & Absorption • Small intestine • Pancreatic enzymes • Trypsinogen  trypsin • Chymotrypsinogen  chymotrypsin • Procarboxypeptidases A & B  carboxypeptidases • Proelastase • Collagenase • Brush border peptidases • Aminopeptidases, dipeptdylaminopeptidases, tripeptidases • Tripeptides hydrolyzed or absorbed at brush border 2009 Cengage-Wadsworth

  13. Digestion & Absorption • Intestinal brush border membrane amino acid & peptide absorption • Amino acid transport • Carriers required - passive & active transporters • Peptide transport • PEPT1 • Co-movement of protons (H+) 2009 Cengage-Wadsworth

  14. Digestion & Absorption • Intestinal basolateral membrane transport of amino acids • Diffusion & sodium-independent transport are main modes • Intestinal cell amino acid use • Cells use or partially metabolize for release into blood 2009 Cengage-Wadsworth

  15. Digestion & Absorption • Intestinal glutamine metabolism • Primary energy source for enterocytes • Intestinal glutamate metabolism • Intestinal aspartame metabolism • Intestinal arginine metabolism • Intestinal methionine & cysteine metabolism 2009 Cengage-Wadsworth

  16. Digestion & Absorption • Amino acid absorption into extraintestinal tissues • AAs enter portal vein to liver • Transport into hepatocytes • Transport into other cells • -glutamyl cycle 2009 Cengage-Wadsworth

  17. Amino Acid Metabolism • Metabolism of AAs includes: • Protein synthesis • Amino acid catabolism • Hepatic catabolism • Uses of aromatic amino acids • Uses of sulfur-containing amino acids • Uses of branched-chain amino acids • Uses of other amino acids • Plasma amino acids & pools 2009 Cengage-Wadsworth

  18. Synthesis of Plasma Proteins, Nitrogen-Containing Nonprotein Compounds, & Purine & Pyrimidine Bases • Plasma proteins • Albumin • Transthyretin (prealbumin) • Retinol-binding protein • Blood clotting proteins • Immunoproteins • Transport proteins • Acute phase proteins • Stress (heat) shock proteins (hsp) 2009 Cengage-Wadsworth

  19. Synthesis of Plasma Proteins, Nitrogen-Containing Nonprotein Compounds, & Purine & Pyrimidine Bases • Nitrogen-containing nonprotein compounds • Glutathione - antioxidant, reacts with H2O2, AA transport, conversion of prostaglandin H2 to D2 & E2 • Carnitine - FA transport • Creatine - part of phosphocreatine (high-energy compound) 2009 Cengage-Wadsworth

  20. Synthesis of Plasma Proteins, Nitrogen-Containing Nonprotein Compounds, & Purine & Pyrimidine Bases • Carnosine - may be antioxidant • Choline - methyl donor, part of acetylcholine & lecithin & sphingomyelin 2009 Cengage-Wadsworth

  21. Synthesis of Plasma Proteins, Nitrogen-Containing Nonprotein Compounds, & Purine & Pyrimidine Bases • Purine & pyrimidine bases • Main constituents of DNA & RNA • Pyrimidines • 6-membered rings containing N in positions 1 & 3 • Uracil, cytosine & thymidine • Purines • 2 fused rings, N in positions 1, 3, 7, 9 • Adenine & guanine 2009 Cengage-Wadsworth

  22. Protein Synthesis Overview • Insulin & glucagon • Rate of protein digestion • Leucine • Fed vs. fasted state 2009 Cengage-Wadsworth

  23. Amino Acid Catabolism Overview • Transamination &/or deamination of amino acids • Deamination = removal of amino group • Transamination = transfer of amino group from one AA to AA carbon skeleton or -keto acid • Catalyzed by aminotransferases 2009 Cengage-Wadsworth

  24. Amino Acid Catabolism Overview • Disposal of ammonia--the urea cycle • NH3 combines with CO2 or HCO3- to form carbamoyl phosphate • Carbamoyl phosphate reacts with ornithine transcarbamoylase (OTC) to form citruline • Aspartate reacts with citruline to form argininosuccinate • Arginosuccinate is cleaved to form fumarate & arginine • Urea is formed and ornithine is re-formed from cleavage of arginine 2009 Cengage-Wadsworth

  25. Amino Acid Catabolism Overview • An overview of metabolism of the carbon skeleton/-keto acid • Energy generation • Glucose & ketone body production • Cholesterol production • Fatty acid production 2009 Cengage-Wadsworth

  26. Hepatic Catabolism & Uses of Aromatic Amino Acids • Phenylalanine & tyrosine • Phenylalanine converted to tyrosine by phenylalanine hydroxylase • Tyrosine • Degradation begins with transamination to p-hydroxyphenylpyruvate • Tyrosine used in other tissues for synthesis of L-dopa & catecholamines • Melanin, thyroid hormones • Disorders of phenylalanine & tyrosine metabolism 2009 Cengage-Wadsworth

  27. Hepatic Catabolism & Uses of Aromatic Amino Acids • Tryptophan • Catabolized to N-formylkynurenine • This is catabolized to formate & kynurenine • Used for: • Protein synthesis • Energy, glucose, & ketone body production • Synthesis of serotonin & melatonin • Disorders of tryptophan metabolism. 2009 Cengage-Wadsworth

  28. Hepatic Catabolism & Uses of Sulfur (S)-Containing Amino Acids • Methionine • Converted to S-adenosyl methionine • SAM is principal methyl donor • Removal of methyl group yields S-adenosyl homocysteine (SAH) • SAH converted to homocysteine • Homocysteine reacts with serine to form cystathionine • Cystathionine cleaved to form cysteine & -ketobutyrate • Propionyl CoA (made from -ketobutyrate) converted to D-methylmalonyl CoA • Disorders of methionine metabolism 2009 Cengage-Wadsworth

  29. Hepatic Catabolism & Uses of Sulfur (S)-Containing Amino Acids • Cysteine • Used for protein & glutathione synthesis • Converted to cysteine sulfinate, used to produce taurine • Taurine important in retina, functions as bile salt & inhibitory neurotransmitter • Cysteine degradation yields pyruvate & sulfite 2009 Cengage-Wadsworth

  30. Hepatic Catabolism & Uses of the Branched-Chain Amino Acids • Isoleucine, leucine, & valine • Taken up & transaminated primarily in muscles 2009 Cengage-Wadsworth

  31. Hepatic Catabolism & Uses of Other Amino Acids • Lysine • Ketogenic - catabolism yields acetyl CoA • Disorders of lysine metabolism • Threonine • 3 pathways • Disorders of threonine metabolism 2009 Cengage-Wadsworth

  32. Hepatic Catabolism & Uses of Other Amino Acids • Glycine & serine • Produced from one another in reversible reaction requiring folate • Disorders of glycine metabolism • Arginine • Kidney - creatine synthesis • Liver - generation of urea & ornithine • Histidine • Glutamate, carnosine, histamine 2009 Cengage-Wadsworth

  33. Amino Acids Not Taken Up by the Liver: Plasma Amino Acids & Amino Acid Pool(s) • Plasma concentrations rise after a meal • Pool of about 150 g of endogenous + exogenous AAs • Re-use thought to be primary source of AAs for protein synthesis • More nonessential than essential in pool 2009 Cengage-Wadsworth

  34. Interorgan “Flow” of Amino Acids & Organ-Specific Metabolism • Glutamine & the liver, kidneys, & intestine • Ammonia transport • Hypercatabolic conditions • Alanine & the liver & muscle • Inter-tissue transfer of amino groups • Liver: converted to glutamate or glucose 2009 Cengage-Wadsworth

  35. Interorgan “Flow” of Amino Acids & Organ-Specific Metabolism • Skeletal muscle • Isoleucine, leucine, & valine • Nitrogen-containing compounds as indicators of muscle mass & muscle/ protein catabolism 2009 Cengage-Wadsworth

  36. Interorgan “Flow” of Amino Acids & Organ-Specific Metabolism • Kidneys • Serine synthesis from glycine • Glycine catabolism to ammonia • Histidine generation from carnosine degradation • Arginine synthesis from citruline • Tyrosine synthesis from phenylalanine • Guanidoacetate formation from arginine & glycine for creatine synthesis 2009 Cengage-Wadsworth

  37. Brain & Accessory Tissues • Biogenic amines & neurotransmitters/hormones • Tryptophan - melatonin & serotonin • Tyrosine - dopamine, norepinephrine, epinephrine • Glysine - inhibitory neurotransmitter • Taurine - inhibitory neurotransmitter • Aspartate - excitatory neurotransmitter • Glutamate - excitatory neurotransmitter or converted to -amino butyric acid (GABA) 2009 Cengage-Wadsworth

  38. Brain & Accessory Tissues • Neuropeptides • Hormone-releasing factors • Endocrine effects • Modulatory actions on transmitter functions, mood or behavior • Neurosecretory cells of hypothalamus secrete • Synthesized from AAs via DNA codes 2009 Cengage-Wadsworth

  39. Protein Turnover: Synthesis & Catabolism of Tissue Proteins • Food intake & nutritional status • Hormonal mediation • AA pools connect 2 cycles of N metabolism: • Protein turnover • Nitrogen balance • Protein synthesis & degradation controlled separately 2009 Cengage-Wadsworth

  40. Protein Turnover: Synthesis & Catabolism of Tissue Proteins • Cellular protein degradation systems • Lysosomal degradation • Proteasomal degradation • Calcium or calcium-activated proteolytic degradation 2009 Cengage-Wadsworth

  41. Changes in Body Mass with Age • Lean body mass increases throughout childhood • Changes in total fluid & ECF/ICF • Gender differences develop during adolescence • Greater increase in males • After 25, weight gain = fat gain • Lean mass decreases with increasing age • More so in women than men • Body water declines too 2009 Cengage-Wadsworth

  42. Protein Quality & Protein Intake • Foods can be categorized as: • High-quality or complete proteins • Low-quality or incomplete proteins • Evaluation of protein quality • Nitrogen balance/nitrogen status • Chemical or amino acid score • Protein digestibility corrected amino acid score 2009 Cengage-Wadsworth

  43. Protein Quality & Protein Intake • Protein efficiency ratio • Biological value • Net protein utilization • Net dietary protein calories percentage • Protein information on food labels • % Daily Value 2009 Cengage-Wadsworth

  44. Protein Quality & Protein Intake • Recommended protein & amino acid intakes • RDA for adults = 0.8 g/kg • AI for birth-6 months • RDA for indispensible AAs • Negative effects of high protein intakes controversial (no UL) • AMDR = 10%-35% kcal 2009 Cengage-Wadsworth

  45. Protein Quality & Protein Intake • Protein deficiency/malnutrition • Kwashiorkor • Adequate energy with insufficient protein • Edema owing to loss of blood proteins • Marasmus • Wasting, emaciation • Chronic insufficiency of energy & protein 2009 Cengage-Wadsworth

  46. Perspective 6 Protein Turnover:Starvation Compared with Stress 2009 Cengage-Wadsworth

  47. Starvation vs. Stress • Starvation • Protein synthesis decreases • Hormone balance adjusts • Adaptation - muscle catabolism slows • Stress • Hypermetabolism • Lipolysis doesn’t lead to ketosis • Muscle catabolism undiminished • Protein turnover - immune response & acute phase response 2009 Cengage-Wadsworth

More Related