CHAPTER 7-- PROTEINOverview of Protein• Named from Greek protos – to come first• 17% of body weight• Body is made up of thousands of proteins found in: - Muscle- Connective tissue- Organs- DNA- Hgb- Antibodies- Enzymes• Regulates and maintains body FCNStructure of Protein• Made up of C, H, O and nitrogen• Compromised of amino acids• Building blocks of proteins• AA arranged in chains- 20 AA in humansStructure of Amino Acids• Basic (or “generic”) structure- Carbon skeleton- 1 C, 1 H, and side chain (R)- Amino group: contains nitrogen- Acid group: carboxylAmino Acids• Nonessential amino acids (11)- Body can produce- Not needed in the diet• Essential amino acids (9)- Must be taken in through food- Not synthesized by the body• Conditionally Essential amino acids- Essential during infancy, disease or traumaSynthesis of Nonessential Amino Acids• Transamination- Transfer of amino group from one AA to a carbon skeleton to form a new AA• Deamination- The AA losing the amine group without transferring it to a carbon skeleton- Amine group is incorporated into urea in the liver- Excreted in urineComplete and Incomplete Proteins• Complete proteins- high biological value (BV)- Adequate amounts of all essential AA- Animal proteins, except gelatin- Similar to our protein, so easily absorbed• Incomplete proteins- low biological value- Inadequate amounts of one or more essential AA- Plant proteins, except soybeans and quinoa• Complementary proteins- Combining incomplete proteins to compensate for the limiting amino acidLimiting Amino Acid• Essential AA that is missing or in the smallest supply• Slows or halts protein synthesisProtein Synthesis• Proteins are long chains of amino acids• Amino acids are joined to each other by peptide bonds- amino group + acid (carboxyl) group- Di-,tri-,oligo-, & polypeptide- The structure of each protein is dictated by the DNA of a gene• Determined via gene expression- Transcription: mRNA copies the genetic information from DNA- Translation: The genetic information in RNA is convertedCHAPTER 7-- PROTEINinto the amino acids sequence of proteinGenetic Disease • Some genetic disease can result in protein abnormalities• Ex: sickle cell anemiaProtein Organization • Primary Structure- sequence of amino acids- Determines shape of protein• Secondary Structure- How AA sequence folds locally- Forms spiral shape• Tertiary Structure- unique 3D folding of the secondary structure elements- Determines function• Quaternary Structure- 2 or more separate polypeptide chains interact to form a large, new protein- Activates FCN- Ex: Hgb—4 polypeptidesDenaturation of Proteins• Alteration of tertiary (3D) protein structure• Benefits : digestion, safety• Cons : can alter normal FCNProtein Turnover- Protein synthesis response to changing conditions• Constant state of breakdown, rebuldingand repair• Allows adaptions in response to diet, exercise, injury, illness, etc• Ingested proteins are degraded to provide building blocks for new proteinsSources of Protein• Diet and recycling of body protein• North American: 70% supplied by meat, poultry, fish, milk and milk products, legumes, and nuts• Worldwide : 35% of protein comes fromanimal sources• Incorporate more plant than animals because more cholesterol and fiberEvaluation of Food Protein Quality• Protein quality is typically defined as a protein’s capacity to provide essential amino acids to an individual• Biological Value (BV)- Egg white is highest (BV 100)- All N absorbed is retained and used in body protein• Protein Efficiency Ratio (PER)- Equation: gain in body mass/protein intake• Chemical Score- mg limited AA test; Pro/mg limiting AA “ideal Pro”• Protein Digestibility Corrected AminoAcid Score (PDCAAS)- Chemical score x digestibility - Preferred “best” methodRecommended Intakes of Protein• Positive Nitrogen Balance- N (protein) intake > N (protein) loss• Negative Nitrogen Balance- N (protein) intake < N (protein) loss• Equilibrium - N (protein) intake = N (protein) lossProtein Needs• AMDR (IOM): 10-35% kcals• Adult RDA- 0.8 g/kg healthy body weight- Weight in lbs/2.2 = weight in kg• Recovery states- 0.8-2 g/kg body weight• Endurance or strength athletesCHAPTER 7-- PROTEIN- 0.8-1.7 g/kg body weight• Excess protein from diet or supplemental sources cannot be stored as protein. It is used as fuel (glucose) or stored as fat.Protein Digestion• Cooking denatures proteins- Heat and acids• Protein digestion begins in the stomach- Gastrin: hormone secreted by stomach to stimulated gastric juice production- HCL denatures proteins & activates pepsin- Pepsin: enzyme that breaks down long polypeptide chains into shorter chains• Small intestine- Chyme triggers release of secretin &CCK- Both stimulate release of pancreatic proteases (trypsin, chymotrypsin, carboxypeptidase)- Polypeptides à short peptides + amino acidsProtein Absorption• Short peptides + amino acids in the lumen of SI are absorbed into absorptive cells- Via active transport- polypeptidase breaks down short peptides in AA(Polypeptides à short peptides à AAs)• AAs travel via the portal vein (To what?)- Used for protein synthesis, NRG, conversion to CHO or fat, or released into the bloodstream for other cellsFunctions of Proteins• Producing vital body structures• Maintaining fluid balance• Contributing to acid-base balance- buffers• Forming hormones, enzymes, & neurotransmitters• Contributing to immune function• Transporting nutrients- Carrier proteins • Forming glucose- gluconeogenesis• Providing energy 4 kcals/gHealth Concerns Related to Protein Intake• Protein Energy Malnutrition- Kwashiorkor: protein deficit with moderate energy deficit- Marasmus: protein & energy deficit• High-Protein Diets- Food and Nutrition Board rec’s = Nomore than 35% total kcals from protein- Excess protein does notprovide health benefits- Increases health and disease risk- Damage kidneys: excrete excess nitrogen as urea, overburden kidney capacity to excrete- water is needed to dilute urea- increases risk of dehydration- If high animal-protein = likely low plant foods- Low in: phytochemicals, fiber, vitamins- High in sat fat & cholesterol- Increases risk for CVD and certain cancers- increases urinary Ca loss- Leads to: bone loss, osteoporosis, kidney stones- If excessive AA supplementation cancause AA imbalances and toxicity (methionine, cysteine,