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Protein Structure

Protein Structure. Pages 36-53 in textbook. Protein. Composed of C, H, O, N, (S, P) Component of every body tissue Vary widely in chemical composition, physical properties, size, shape, solubility and biological function Common unit = amino acid 20 commonly found

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Protein Structure

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  1. Protein Structure Pages 36-53 in textbook

  2. Protein • Composed of C, H, O, N, (S, P) • Component of every body tissue • Vary widely in chemical composition, physical properties, size, shape, solubility and biological function • Common unit = amino acid • 20 commonly found • 10 required in animal diets

  3. Protein • Approximately 50% of DM in most animal cells is protein • Exception? adipocytes!! • Made of 20+ amino acids (AA) • Peptide bond • The sequence of amino acids determines the function of the particular protein in the body

  4. Biological Functions of Proteins • Principal organic chemical constituents of body organs and soft tissues • Enormous functional diversity • Cell membrane structure and function • Enzymes • Hormones and other chemical messengers • Immune factors (antibodies) • Fluid balance • Acid-base balance • Transport • Source of energy and glucose

  5. Structural and Mechanical • Collagen • Bone and skin • Keratin • Hair and nails • Motor proteins • Make muscles work!

  6. Enzymes • Proteins that catalyze (speed up) chemical reactions without being used up or destroyed in the process • Anabolic (putting things together) and catabolic (breaking things down) functions • Examples • Digestion • Salivary amylase • Trypsin

  7. Hormones • Chemical messengers that are made in one part of the body but act on cells in other parts of the body • Note that "steroid hormones" are not proteins! • Examples • Insulin • CCK • Some reproductive hormones

  8. Receptors, Carriers • Transport materials across cell membranes

  9. Transport Proteins • Transport substances in the blood • Lipoproteins (transport lipids) • Hemoglobin (transports oxygen and carbon dioxide)

  10. Fluid Balance • Proteins in the blood help maintain appropriate fluid levels in the vascular system • Fluid is forced into tissue spaces by blood pressure generated by pumping action of the heart • Fluid returns to blood because of “osmotic pressure”

  11. Acid-Base Balance • Body works to keep pH of blood near 7.45 • Homeostasis IMPORTANT • Proteins help “buffer” blood to keep pH acceptable

  12. Immune Function (Antibodies) • Antibodies are proteins that attach to and inactivate bacteria and viruses that cause infection

  13. Source of Glucose • When excess protein is fed… • Some amino acids converted to glucose

  14. Source of Energy • Proteins are the last to be used for energy! • Occurs in starvation and low carbohydrate diets

  15. Building blocks of protein Structure: Amino Acids Amine group Carboxyl group

  16. Amino Acid – Structural Isomers • L-isomer found in nature and used in the animal body

  17. Classification Structure Net charge Polarity Essentiality Neutral Aliphatic Aromatic Sulfur Acidic Basic Heterocyclic Classification of Amino Acids

  18. Essentiality • Essential • Amino acids not synthesized in sufficient amounts in the animal’s body • Required in the diet • Nonessential • Adequately synthesized in the tissue • No specific requirement • Vary by species

  19. Arginine Histidine Isoleucine Leucine Lysine Phenylalanine Threonine Tryptophan Valine Methionine Essential Amino Acids

  20. Conditionally Essential Amino Acids • Amino acids that can become essential in certain physiologic conditions • Example: taurine in cats • Example: proline in young pigs • Example: tyrosine becomes essential in people with “phenylketonuria (PKU)” • PKU; 1 in 15,000 babies • Hydroxylation of phenylalanine normally forms tyrosine • Tyrosine important in adrenaline, noradrenaline, thyroxine and melanin synthesis

  21. Phenylalanine (essential aa) Tyrosine (nonessential aa) Phenylketonuria (PKU) • Normal situation: Phenylalanine (essential aa) Tyrosine (nonessential aa) • In PKU: • Phenylalanine builds up Can cause mental retardation Condition inherited from parents (genetic)

  22. PKU Symptoms • VERY FEW symptoms if diagnosed early and diet strictly regulated • IF NOT: • Lighter skin, hair and eyes than siblings • Phenylalanine important in synthesis of melanin • Delayed mental and social skills • Head size significantly below normal • Hyperactivity • Jerking movements of the arms or legs • Mental retardation (severe if not diagnosed and treated early) • Seizures • Skin rashes • Tremors • Unusual positioning of hands

  23. PKU Treatment • EXTREMELY low phenylalanine intake • Diet for life • Special low-phenylalanine infant formula • Used for life • Low or no milk, eggs • No aspartame (NutraSweet) • Fish oil supplements • Hard to get enough essential fatty acids on low phenylalanine diet • Iron supplements

  24. Primary (10) Sequence of amino acids Secondary (20) Twisting of chains into coiled structures α helix Β sheet H bonding Tertiary (30) Grouping of secondary structures Secondary structures coil and fold into layers H and disulfide bonds Quaternary (40) Several tertiary structures linked Large complex proteins Protein Structure

  25. Protein Structures

  26. Denaturation of Protein • “Native” form of protein most biologically active • Disruption of the 3-D structure destroys the function • Denaturation = break H bonds • Heat • Chemicals

  27. Protein Definitions Crude protein (CP) Total N-containing compounds in a feed To calculate the protein percentage, a feed is first chemically analyzed for N content

  28. Protein Definitions Unavailable protein or insoluble crude protein Calculated from N that is bound to the acid detergent fiber (ADF) fraction of the feed Normally, about 1% protein on a DM basis is found in this fraction Values greater than 1% indicate heat damage

  29. Protein Definitions  Available protein Determined by subtracting unavailable protein from crude protein

  30. Protein Definitions Rumen degradable protein (RDP) Protein or N that is degraded in the rumen by microorganisms and incorporated into microbial protein or freed as ammonia

  31. Degradation of Protein

  32. Protein Definitions Soluble protein The protein fraction composed of both non-protein nitrogen (NPN) and true proteins that are rapidly degraded in the rumen It is normally expressed as a percent of the crude protein

  33. Protein Definitions Rumen undegradable protein (RUP) Protein or N that is not degraded in the rumen by microorganisms but is available to be digested by the ruminant

  34. Protein Definitions  Non-protein nitrogen (NPN) All nitrogen fed to animals is not necessarily found in proteins NPN reflects other sources of nitrogen An important source of NPN in the ruminant diet is urea Rumen bacteria can utilize many NPN sources to produce microbial proteins, thus providing amino acids to the cow

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