Y khoa, dược - Chapter 6: Proteins and amino acids: function follows form

Chapter 6 Proteins and Amino Acids: Function Follows FormWhy Is Protein Important?Major component of all plant and animal issuesVital to many aspects of healthProvide energy and help keep skin, hair, and nails healthyDeficiency leads to wastingExcess protein intake a greater problem in the U.S.Amino Acids Are the Building Blocks of ProteinsProteins are sequences of amino acids (AA)20 different amino acids9 essential amino acidsBody cannot make themMust get them through diet11 nonessential amino acidsDo not need to be supplied by dietIf body cannot make them, categorized as conditionally essential amino acidsAmino Acids as Building BlocksAmino acid structureOne central carbon atomOne hydrogen atom (H)One carboxylic acid group (-COOH)One amino group (-NH2)One side group unique to each amino acidSide group gives the amino acid its identityProtein StructureAmino Acid SequenceEach amino acid is joined to the next by a peptide bondPeptide bondsDipeptide (2 AA)Oligopeptide (3 AA)Polypeptide (4-10 AA)Protein StructureProtein ShapeSequence and properties of AA determines protein shapeShape determines protein’s functionProtein DenaturationDenaturationDisrupts shapeProtein unfolds and loses its shape (denature)Caused by acidic or alkalinity, high temperature, alcohol, oxidation, and agitationFunctions of Body ProteinsEach protein has a specific function determined by its unique shapeFunctions of Body ProteinsStructural and mechanical functionsCollagenMost abundantGives skin and bone their elastic strengthKeratinPrimary constituent of hair and nailsMotor proteinsTurn energy into mechanical workFunctions of Body ProteinsImmune functionsAntibodiesBlood proteins that attack and inactivate bacteria and virusesPart of the body’s immune responseFunctions of Body ProteinsEnzymesCatalyze, or speed up, chemical reactionsEvery cell contains thousands of types of enzymesFunctions of Body ProteinsHormonesRegulate body processesAcid-base balanceProteins help maintain stable pH levels by acting as buffersAcidosis or alkalosis occurs when proteins unable to fulfill buffer functionFunctions of Body ProteinsTransport functionsProteins act as Channels and pumps, allowing substances to flow through membranesCarriers, transporting important substances in the blood streamFunctions of Body ProteinsFluid BalanceFluids found inside and outside cellsInside cells: intracellular fluidOutside cells: extracellularTwo types:Interstitial fluid (between cells)Intravascular fluid (in the blood)Functions of Body ProteinsFluid BalanceBlood proteins maintain appropriate fluid levels in vascular systemEdema results when diet lacks enough protein to maintain normal levels of blood proteinsEdema: Swelling caused by buildup of fluid between cellsFunctions of Body ProteinsSource of Energy and GlucoseCarbohydrates and fat are protein-sparingBody prefers burning them for energyWill resort to burning protein for energy if necessaryBody readies protein for use as energy through deaminationRemoval of amino group from an amino acidProtein Digestion and AbsorptionProtein digestionIn the stomachProteins are denatured by hydrochloric acidPepsin begins digestion 10–20% of digestionIn the small intestineProteases and intestinal lining cells break down large peptides into smaller peptidesProtein Digestion and AbsorptionUndigested ProteinPass out of the body in fecesDiseases of the intestinal tract cause problems with digestion by decreasing absorption efficiencyCeliac diseaseCystic fibrosisProtein Digestion and AbsorptionAmino Acid and Peptide AbsorptionTravel via portal vein to liver  released into general circulationProtein in the BodyProtein SynthesisAA assembled in specific sequenceDraws on AA pool as neededDispensable AA missingCell will make that AA or obtain it from the liverProtein in the BodyProtein SynthesisDraws on AA pool as neededIndispensable AA missingBody may break its own protein down to supply the missing AAIndispensable AA unavailableProtein synthesis halts and partially completed protein used elsewhere in the bodyProtein in the BodyAmino Acid Pool and Protein TurnoverThe AA poolAvailable AAProtein synthesis; produce energy and glucoseProtein turnoverConstant recycling of proteinProtein in the BodySynthesis of Nonprotein MoleculesAmino acids as precursors of DNA, RNA, and coenzymesAlso used to make neurotransmitters:Chemicals that send signals from nerve cells to other parts of the bodyProtein in the BodyProtein and Nitrogen ExcretionBreakdown of amino acidsRemoves nitrogen (amino) groupAmino groups converted to urea for excretionProtein in the BodyNitrogen BalanceNitrogen intake vs. nitrogen outputNitrogen equilibriumNitrogen intake = nitrogen outputHealthy adultsProtein in the BodyPositive nitrogen balanceNitrogen intake > nitrogen outputGrowth; recovery from illnessNegative nitrogen balanceNitrogen intake < nitrogen outputInjury and illnessProtein in the DietRecommended Intakes of ProteinAdult RDA = 0.8 gram per kilogram of body weightSevere physical stress can increase body’s need for proteinsInfections, burns, fevers, surgery increase protein lossesDiet must replace lost proteinProtein in the DietProtein Consumption in the United StatesGenerally higher than recommended rangeProtein in the DietProtein QualityComplete ProteinsSupply all indispensable amino acidsAnimal proteins; soy proteinsIncomplete and Complementary ProteinsLow in one or more indispensable amino acidsMost plant proteinsProtein in the DietProtein QualityComplementary proteinsTwo incomplete proteins can equal a complete proteinOne makes up for the other’s lack of specific essential amino acidsCombination then provides sufficient amounts of all essential amino acidsProtein in the DietProtein QualityEvaluating Protein Quality and DigestibilityProvides all the indispensable amino acids at amounts the body needsProvides enough other amino acids to serve as nitrogen sources for making dispensable amino acidsShould be easy to digestConsider the protein digestibility-corrected amino acid score (PDCAAS)Protein in the DietProteins and AAs as Additives and SupplementsProtein and AA additivesStructure, texture, and taste of foodsProtein and AA supplements Used for a variety of reasons: dieters, athletes, certain diseasesRisks unknownVegetarian EatingWhy People Become VegetariansVarious reasons, includingReligious beliefsEnvironmental concernsAversion to eating another living creatureConcerns about animal cruelty concernsIn some cases a necessityVegetarian EatingHealth Benefits of Vegetarian DietsLess fat, saturated fat, and cholesterol intakeMore magnesium and folateMore antioxidantsMore fiber and phytochemicalsReduces risk for heart disease, obesity, hypertension, and cancerVegetarian EatingHealth Risks of Vegetarian DietsVegan diets may be low in some nutrientsCalcium, iron, zinc, vitamin D, and vitamin B12Higher intake of phytatesMore restrictive food choices = less nutrientsCareful planning needed for growth and overall healthVegetarian EatingDietary Recommendations for VegetariansChoose a variety of foodsChoose whole, unrefined foodsChoose a variety of fruits and vegetablesChoose lower-fat dairy products and eggs in moderationConsume a regular source of vitamins B12 and DFortified foods or supplementsHealth Effects of Too Little or Too Much ProteinProtein-Energy MalnutritionKwashiorkorEdema and other signsBetween ages of 18 and 24 monthsAssociated with extreme povertyHealth Effects of Too Little or Too Much ProteinProtein-Energy MalnutritionMarasmusChronic PEMInfants and 6- to 18-month-old childrenAdults with cancer or starvationHealth Effects of Too Little or Too Much ProteinHealth Effects of Excess Dietary ProteinKidney functionIncreases kidney filtration rate, straining functionMineral lossesLink between high-protein diet and osteoporosisHealth Effects of Too Little or Too Much ProteinHealth Effects of Excess Dietary ProteinObesityCorrelation with body fatHeart diseaseIncreased saturated fat and cholesterol intakeCancerIncreased risk for certain types of cancer