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SC EXSC 223 - Chapter 24

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NutritionMost ingested nutrients used for metabolic fuelSome for cell structures and molecular synthesisEnergy value measured in kilocalories (kcal)Heat needed to raise temperature of 1kg H2O by 1 degree CelsiusNutrient: substance in food for growth, maintenance, repairMacro nutrients: bulk of ingested food; carbohydrates, lipids, and proteinsOther (micro) nutrients: required in small amounts; vitamins and mineralsWater required so technically a nutrientFood groups:FruitsVegetablesGrainsProteinDairyEssential vs. non-essential nutrientsEssential nutrients: not synthesized (in sufficient quantity) by liverDiet must providePossibly 50 moleculesNon essential nutrients: synthesized by liverNot necessary in dietNutrients vital to life as wellSummary of carbohydrate, lipid, and protein nutrientsStarch: complex carbohydrates in grains and vegetablesSugars: mono and disaccharides in fruits, sugarcane, sugar beets, honey and milkInsoluble fiber: cellulose in vegetables; provide roughageSoluble fiber: pectin in apples and citrus fruits; reduces blood cholesterol levelsSmall amounts in milk sugar; glycogen in meatsCarbohydrates: uses in the bodyCarbohydrates are made from monosaccharidesGlucose: fuel used by cells to make ATPNeurons and RBCs use only glucose for fuelExcess glucose converted to glycogen or fat and storedFructose and galactose converted to glucose by liver before-circulationFatTriglycerides from plants=liquidTriglycerides from animals=solidsFat and CholesterolTriglyceride made of three fatty acids: saturated fatty acid (no double bonds between carbons; very hydrophobic) monounsaturated and polyunsaturated (not linear)Cis and trans fatty acids;Glycerol backboneTriglyceride: two saturated and one unsaturated with glycerol backboneHave to be shuttled across membrane to enter cellCholesterol: hydrophobic molecule; helps stabilize membrane; derivative of hormone steroidLipidsLiver can convert one fatty acid to another for manyEssential fatty acidsLinoleic: omega-6Linolenic acid: omega-3 fatty acidMany vegetable oils and fishLipids are necessaryHelp absorb fat soluble vitaminsMajor fuel of hepatocytes and skeletal musclePhospholipids essential in myelin sheaths and all cell membranesAdipose tissue: protection, insulation, fuel storageProstaglandins: blood pressure control, inflammationCholesterol stabilizes membranes; precursor of bile salts, steroid hormonesFats: 30% or less of total caloric intakeSaturated fats: 10% or less of total fat intakeCholesterol: no more than 300 mg/dayTypical American diet: greater than 40% total caloriesGoal: keep blood cholesterol less than 200mgLipids: fat substitutesFat substitutesAir (beaten into foods)Modified starches and gumsMilk whey proteinOlestra: made from cottonseedsGum derivatives and olestra not metabolizedRest metabolized-caloriesDisadvantagesCannot withstand high heat of cookingTaste differs from real fatsGas diarrheaMay interfere with fat-soluble vitamins, beta carotene absorptionProteinsUses in bodyStructural materialsKeratin (skin); collagen and elastin (connective tissue); muscle proteinsFunctional moleculesEnzymes, some hormonesAmino acids can be burned for energyUse of amino acidsAll or none ruleAll amino acids needed must be present for protein synthesis to occur; if not all present amino acids used for energyAdequacy of caloric intakeProtein used as fuel if insufficient carbohydrate or fat availableNitrogen balanceRate of protein synthesis equals rate of breakdown and lossPositive nitrogen balance: synthesis exceeds breakdown; normal in children, pregnant women, tissue repairNegative nitrogen balance: breakdown exceeds synthesis; ex. stress, burns, infection, injury, poor dietary proteins, starvation)Hormonal controlsAnabolic hormonesGH and sex hormones accelerate protein synthesis and growthCatabolic hormonesAdrenal glucocorticoids (released during stress) stimulate protein breakdown; conversion of amino acids to glucose8 our of 20 amino acids are essential amino acidssome amino acids are conditionally essentialmost readily available through plant and animal sourcesDietary requirementsNeeds reflect age, size, metabolic rate, nitrogen balanceRule of thumb: daily intake of 0.8g per kg body weightAmerican diet provides more than neededVitaminsOrganic compoundsCrucial in helping body use nutrientsMost function as coenzymesVitamin D (skin), some B and K synthesized by intestinal bacteria; beta-carotene (carrots) converted in body-vitamin ARest must be ingestedNo one food group contains all vitaminsTwo types based on solubility:Water soluble vitaminsB complex and C are absorbed with waterB12 absorption requires intrinsic factorNot stored in the bodyAny not used within one hour-excretedMegadoses uselessFat soluble vitaminsA, D, E, and K absorbed with lipid digestion productsfree radicals generated during normal metabolismvitamins C, E, A and mineral selenium are antioxidantsneutralize free radicalsbroccoli, cauliflower, brussel sprouts good sources of vitamins A and CMineralsSeven required in moderate amountsCalcium, phosphorous, potassium, sulfur, sodium, chlorine, and magnesiumAll other required in trace amountsWork with nutrients to ensure proper body functioningUptake and excretion balanced to prevent toxic overloadMinerals examplesCalcium, phosphorous, and magnesium slats harden boneIron essential for oxygen binding to hemoglobinIodine necessary for thyroid hormone synthesisSodium and chloride major electrolytes in bloodMineral rich foodsvegetables, legumes, milk, and some meatsWhat do you mean when we talk about metabolismMetabolism: biochemical reaction inside cells involving nutrientsTwo types of reactions:Anabolism: synthesis of large molecules from small onesEx. amino acids: proteinsEx. glucose: glycogenCatabolism: hydrolysis of complex structures to simpler onesEx. proteins: amino acidsEx. glucose: co2 and h20Cellular respiration:Catabolism food to form (anabolism) ATP in cellsC6H12O6 + 02----CO2 + H2O and ADP +Pi---ATPWe use ATP to drive reactions (cross-bridge cycling) or to regulate enzymes (phosphorylationPhosphorylated molecules activated to perform cellular functionsOxidation-Reduction (redox) reactionsOxidation: gain of 02 or lose H+ and e-Reduction: gain H+ and e- or lose O2Hydrogen and electrons travel togetherOxidation-reduction (redox) reactions: enzymesDehyrogenases: removal of hydrogen atomsOxidases: transfer of oxygenRequire help: usually vitamin B derivativesCoenzymes act as hydrogen (or electron)


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