Presentation on theme: "Chapter 25 Metabolism Functions of food source of energy"— Presentation transcript:
1 Chapter 25 Metabolism Functions of food source of energy essential nutrientsstored for future useMetabolism is all the chemical reactions of the bodysome reactions produce the energy stored in ATP that other reactions consumeall molecules will eventually be broken down and recycled or excreted from the body
2 Catabolism and Anabolism Catabolic reactions breakdown complex organic compoundsproviding energy (exergonic)glycolysis, Krebs cycle and electron transportAnabolic reactions synthesize complex molecules from small moleculesrequiring energy (endergonic)Exchange of energy requires use of ATP (adenosine triphosphate) molecule.
3 ATP Molecule & EnergyEach cell has about 1 billion ATP molecules that last for less than one minuteOver half of the energy released from ATP is converted to heat
4 Energy Transfer Energy is found in the bonds between atoms Oxidation is a decrease in the energy content of a moleculeReduction is the increase in the energy content of a moleculeOxidation-reduction reactions are always coupled within the bodywhenever a substance is oxidized, another is almost simultaneously reduced.
5 Mechanisms of ATP Generation ADP + P = ATPPhosphorylation isbond attaching 3rd phosphate group contains stored energyMechanisms of phosphorylationwithin animalssubstrate-level phosphorylation in cytosoloxidative phosphorylation in mitochondriain chlorophyll-containing plants or bacteriaphotophosphorylation.
6 Phosphorylation in Animal Cells In cytoplasm (1)In mitochondria (2, 3 & 4)
7 Carbohydrate Metabolism--In Review In GI tractpolysaccharides broken down into simple sugarsabsorption of simple sugars (glucose, fructose & galactose)In liverfructose & galactose transformed into glucosestorage of glycogen (also in muscle)In body cells --functions of glucoseoxidized to produce energyconversion into something elsestorage energy as triglyceride in fat
8 Fate of Glucose ATP production during cell respiration uses glucose preferentiallyConverted to one of several amino acids in many different cells throughout the bodyGlycogenesishundreds of glucose molecules combined to form glycogen for storage in liver & skeletal musclesLipogenesis (triglyceride synthesis)converted to glycerol & fatty acids within liver & sent to fat cells
9 Glucose Movement into Cells In GI tract and kidney tubules, Na+/glucose symportersMost other cells, GluT facilitated diffusion transporters move glucose into cellsinsulin increases number of GluT transporters in the membrane of most cellsin liver & brain, always lots of GluT transportersGlucose 6-phosphate forms immediately inside cell (requires ATP) thus, glucose hidden in cellConcentration gradient favorable for more glucose to enter
10 Glucose Catabolism Cellular respiration Anaerobic respiration 4 steps are involvedglucose + O2 produces H2O + energy + CO2Anaerobic respirationcalled glycolysis (1)formation of acetyl CoA (2) is transitional step to Krebs cycleAerobic respirationKrebs cycle (3) and electron transport chain (4)
11 Glycolysis of Glucose & Fate of Pyruvic Acid Breakdown of six-carbon glucose molecule into 2 three-carbon molecules of pyruvic acid10 step process occurring in cell cytosolproduces 4 molecules of ATP after input of 2 ATPutilizes 2 NAD+ molecules as hydrogen acceptorsIf O2 shortage in a cellpyruvic acid is reduced to lactic acid so that NAD+ will be still available for further glycolysisrapidly diffuses out of cell to bloodliver cells remove it from blood & convert it back to pyruvic acid
12 Formation of Acetyl Coenzyme A Pyruvic acid enters the mitochondria with help of transporter proteinDecarboxylationpyruvate dehydrogenase converts 3 carbon pyruvic acid to 2 carbon fragment (CO2 produced)pyruvic acid was oxidized so that NAD+ becomes NADH2 carbon fragment (acetyl group) is attached to Coenzyme A to form Acetyl coenzyme A which enter Krebs cyclecoenzyme A is derived from pantothenic acid (B vitamin).
13 Krebs Cycle (Citric Acid Cycle) Series of oxidation-reduction & decarboxylation reactions occurring in matrix of mitochondriaIt finishes the same as it starts (4C)acetyl CoA (2C) enters at top & combines with a 4C compound2 decarboxylation reactions peel 2 carbons off again when CO2 is formed
14 Krebs CycleEnergy stored in bonds is released step by step to form several reduced coenzymes (NADH & FADH2) that store the energyIn summary: each Acetyl CoA molecule that enters the Krebs cycle produces2 molecules of C02one reason O2 is needed3 molecules of NADH + H+one molecule of ATPone molecule of FADH2Remember, each glucose produced 2 acetyl CoA molecules
15 The Electron Transport Chain Series of integral membrane proteins in the inner mitochondrial membrane capable of oxidation/reductionEach electron carrier is reduced as it picks up electrons and is oxidized as it gives up electronsSmall amounts of energy released in small stepsEnergy used to form ATP by chemiosmosis
16 ChemiosmosisSmall amounts of energy released as substances are passed along inner membraneEnergy used to pump H+ ions from matrix into space between inner & outer membraneHigh concentration of H+ is maintained outside of inner membraneATP synthesis occurs as H+ diffuses through a special H+ channel in inner membrane
17 Steps in Electron Transport Carriers of electron transport chain are clustered into 3 complexes that each act as proton pump (expel H+)Mobile shuttles pass electrons between complexesLast complex passes its electrons (2H+) to a half of O2 molecule to form a water molecule (H2O)
18 Proton Motive Force & Chemiosmosis Buildup of H+ outside the inner membrane creates + chargeelectrochemical gradient potential energy is called proton motive forceATP synthase enzyme within H+ channel uses proton motive force to synthesize ATP from ADP and P
19 Summary of Cellular Respiration Glucose + O2 is broken down into CO2 + H2O + energy used to form 36 to 38 ATPs2 ATP are formed during glycolysis2 ATP are formed by phosphorylation during Krebs cycleelectron transfers in transport chain generate 32 or 34 ATPs from one glucose moleculeSummary in Table 25.1Points to rememberATP must be transported out of mitochondria in exchange for ADPuses up some of proton motive forceOxygen is required or many of these steps can not occur
20 Carbohydrate LoadingLong-term athletic events (marathons) can exhaust glycogen stored in liver and skeletal musclesEating large amounts of complex carbohydrates (pasta & potatoes) for 3 days before a marathon maximizes glycogen available for ATP productionUseful for athletic events lasting for more than an hour
21 Glycogenesis & Glycogenolysis glucose storage as glycogen4 steps to glycogen formation in liver or skeletal musclestimulated by insulinGlycogenolysisglucose release not a simple reversal of stepsenzyme phosphorylase splits off a glucose molecule by phosphorylation to form glucose 1-phosphateenzyme only in hepatocytes so muscle can’t release glucoseenzyme activated by glucagon (pancreas) & epinephrine (adrenal)
22 GluconeogenesisLiver glycogen runs low if fasting, starving or not eating carbohydrates forcing formation from other substanceslactic acid, glycerol & certain amino acids (60% of available)Stimulated by cortisol (adrenal) & glucagon (pancreas)cortisol stimulates breakdown of proteins freeing amino acidsthyroid mobilizes triglycerides from adipose tissue
23 Transport of Lipids by Lipoproteins Most lipids are nonpolar and must be combined with protein to be tranported in bloodLipoproteins are spheres containing hundreds of moleculesouter shell polar proteins (apoproteins) & phospholipidsinner core of triglyceride & cholesterol estersLipoprotein categorized by function & density4 major classes of lipoproteinschylomicrons, very low-density, low-density & high-density lipoproteins
24 Classes of Lipoproteins Chylomicrons (2 % protein)form in intestinal epithelial cells to transport dietary fatapo C-2 activates enzyme that releases the fatty acids from the chylomicron for absorption by adipose & muscle cellsliver processes what is leftVLDLs (10% protein)transport triglycerides formed in liver to fat cellsLDLs (25% protein) --- “bad cholesterol”carry 75% of blood cholesterol to body cellsapo B100 is docking protein for receptor-mediated endocytosis of the LDL into a body cellif cells have insufficient receptors, remains in blood and more likely to deposit cholesterol in artery walls (plaque)HDLs (40% protein) --- “good cholesterol”carry cholesterol from cells to liver for elimination
25 Blood Cholesterol Sources of cholesterol in the body food (eggs, dairy, organ meats, meat)synthesized by the liverAll fatty foods still raise blood cholesterolliver uses them to create cholesterolstimulate reuptake of cholesterol containing bile normally lost in the fecesDesirable readings for adultstotal cholesterol under 200 mg/dL; triglycerides mg/dLLDL under 130 mg/dL; HDL over 40 mg/dLcholesterol/HDL ratio above 4 is undesirable riskRaising HDL & lowering cholesterol can be accomplished by exercise, diet & drugs
26 Fate of Lipids Oxidized to produce ATP Excess stored in adipose tissue or liverSynthesize structural or important moleculesphospholipids of plasma membraneslipoproteins that transport cholesterolthromboplastin for blood clottingmyelin sheaths to speed up nerve conductioncholesterol used to synthesize bile salts and steroid hormones.
27 Lipid Anabolism: Lipogenesis Synthesis of lipids by liver cells = lipogenesisfrom amino acidsconverted to acetyl CoA & then to triglyceridesfrom glucosefrom glyceraldehyde 3-phosphate to triglyceridesStimulated by insulin when eat excess calories
28 Ketosis Blood ketone levels are usually very low many tissues use ketone for ATP productionFasting, starving or high fat meal with few carbohydrates results in excessive beta oxidation & ketone productionacidosis (ketoacidosis) is abnormally low blood pHsweet smell of ketone body acetone on breathoccurs in diabetic since triglycerides are used for ATP production instead of glucose & insulin inhibits lipolysis
29 Fate of Proteins Proteins are broken down into amino acids Usage transported to the liverUsageoxidized to produce ATPused to synthesize new proteinsenzymes, hemoglobin, antibodies, hormones, fibrinogen, actin, myosin, collagen, elastin & keratinexcess converted into glucose or triglyceridesno storage is possibleAbsorption into body cells is stimulated by insulinlike growth factors (IGFs) & insulin
30 Protein Catabolism Breakdown of protein into amino acids Liver cells convert amino acids into substances that can enter the Krebs cycledeamination removes the amino group (NH2)converts it to ammonia (NH3) & then ureaurea excreted in the urineConverted substances enter the Krebs cycle to produce ATP
31 Protein AnabolismProduction of new proteins by formation of peptide bonds between amino acids10 essential amino acids are ones we must eat because we can not synthesize themnonessential amino acids can be synthesized by transamination (transfer of an amino group to a substance to create an amino acid)Occurs on ribosomes in almost every cellStimulated by insulinlike growth factor, thyroid hormone, insulin, estrogen & testosteroneLarge amounts of protein in the diet do not cause the growth of muscle, only weight-bearing exercise
32 Phenylketonuria (PKU) Genetic error of protein metabolism that produces elevated blood levels of amino acid phenylalaninecauses vomiting, seizures & mental retardationnormally converted by an enzyme into tyrosine which can enter the krebs cycleScreening of newborns prevents retardationspend their life with a diet restricting phenylalaninerestrict Nutrasweet which contains phenylalanine
33 Metabolic Adaptations Absorptive statenutrients entering the bloodstreamglucose readily available for ATP production4 hours for absorption of each meal so absorptive state lasts for 12 hours/dayPostabsorptive stateabsorption of nutrients from GI tract is completebody must meet its needs without outside nutrientslate morning, late afternoon & most of the eveningassuming no snacks, lasts about 12 hours/daymore cells use ketone bodies for ATP productionmaintaining a steady blood glucose level is critical
34 Metabolism During Fasting & Starvation Fasting means going without food for hours/daysStarvation means weeks or monthscan survive 2 months or more if drink enough wateramount of adipose tissue is determining factorNutritional needsnervous tissue & RBC need glucose so amino acids will be broken down for gluconeogenesisblood glucose stabilizes at 65 mg/100 mLlipolysis releases glycerol used in gluconeogenesisincrease in formation of ketone bodies by liver cells due to catabolism of fatty acidsby 40 days, ketones supply 2/3’s of brains fuel for ATP
35 Absorption of AlcoholAbsorption begins in the stomach but is absorbed more quickly in the small intestinefat rich foods keep the alcohol from leaving the stomach and prevent a rapid rise in blood alcohola gastric mucosa enzyme breaks down some of the alcohol to acetaldehydeFemales develop higher blood alcoholshave a smaller blood volumehave less gastric alcohol dehydrogenase activity
36 Metabolic Rate Rate at which metabolic reactions use energy energy used to produce heat or ATPBasal Metabolic Rate (BMR)measurements made under specific conditionsquiet, resting and fasting conditionBasal Temperature maintained at 98.6 degreesshell temperature is usually 1 to 6 degrees lower
37 Heat ProductionFactors that affect metabolic rate and thus the production of body heatexercise increases metabolic rate as much as 15 timeshormones regulate basal metabolic ratethyroid, insulin, growth hormone & testosterone increase BMRsympathetic nervous system’s release of epinephrine & norepinephrine increases BMRhigher body temperature raises BMRingestion of food raises BMR 10-20%children’s BMR is double that of an elderly person
38 Mechanisms of Heat Transfer Temperature homeostasis requires mechanisms of transferring heat from the body to the environmentconduction is heat exchange requiring direct contact with an objectconvection is heat transfer by movement of gas or liquid over bodyradiation is transfer of heat in form of infrared rays from bodyevaporation is heat loss due to conversion of liquid to a vapor (insensible water loss)
39 Hypothalamic Thermostat Preoptic area in anterior hypothalamusreceives impulses from thermoreceptorsgenerates impulses at a higher frequency when blood temperature increasesimpulses propagate to other parts of hypothalamusheat-losing centerheat-promoting centerSet in motion responses that either lower or raise body temperature
40 Thermoregulation Declining body temperature thermoreceptors signal hypothalamus to produce TRHTRH causes anterior pituitary to produce TSH resulting invasoconstriction in skinadrenal medulla stimulates cell metabolic rateshiveringrelease of more thyroid hormone raises BMRIncreases in body temperaturesweating & vasodilation
41 Hypothermia Lowering of core body temperature to 35°C (95°F) Causes immersion in icy water (cold stress)metabolic diseases (hypoglycemia, adrenal insufficiency or hypothyroidism)drugs (alcohol, antidepressants, or sedatives)burns and malnutritionSymptoms that occur as body temperature dropsshivering, confusion, vasoconstriction, muscle rigidity, bradycardia, acidosis, hypoventilation, coma & death
42 Regulation of Food Intake Hypothalamus regulates food intakefeeding (hunger) centersatiety centerStimuli that decrease appetiteglucagon, cholecystokinin, epinephrine, glucose & leptinstretching of the stomach and duodenumSignals that increase appetitegrowth releasing hormone, opioids, glucocorticoids, insulin, progesterone & somatostatin
43 Guidelines for Healthy Eating Nutrients include water, carbohydrates, lipids, proteins, vitamins and mineralsCaloric intakewomen 1600 Calories/day is neededactive women and most men 2200 Caloriesteenage boys and active men 2800 caloriesFood guide pyramid developed by U.S. Department of Agricultureindicates number of servings of each food group to eat each day
45 Minerals Inorganic substances = 4% body weight Functions calcium & phosphorus form part of the matrix of bonehelp regulate enzymatic reactionscalcium, iron, magnesium & manganesemagnesium is catalyst for conversion of ADP to ATPform buffer systemsregulate osmosis of watergeneration of nerve impulses
46 Vitamins Organic nutrients needed in very small amounts serve as coenzymesMost cannot be synthesized by the bodyFat-soluble vitaminsabsorbed with dietary fats by the small intestinestored in liver and include vitamins A, D, E, and KWater-soluble vitamins are absorbed along with water in the Gl tractbody does not store---excess excreted in urineincludes the B vitamins and vitamin C
47 Antioxidant Vitamins C, E and beta-carotene (a provitamin) Inactivate oxygen free radicalshighly reactive particles that carry an unpaired electrondamage cell membranes, DNA, and contribute to atherosclerotic plaquesarise naturally or from environmental hazards such as tobacco or radiationProtect against cancer, aging, cataract formation, and atherosclerotic plaque
48 Vitamin and Mineral Supplements Eat a balanced diet rather than taking supplementsExceptionsiron for women with heavy menstrual bleedingiron & calcium for pregnant or nursing womenfolic acid if trying to become pregnantreduce risk of fetal neural tube defectscalcium for all adultsB12 for strict vegetariansantioxidants C and E recommended by some
49 Fever Abnormally high body temperature toxins from bacterial or viral infection = pyrogensheart attacks or tumorstissue destruction by x-rays, surgery, or traumareactions to vaccinesBeneficial in fighting infection & increasing rate of tissue repair during the course of a diseaseComplications--dehydration, acidosis, & brain damage.
50 Obesity Body weight more than 20% above desirable standard Risk factor in many diseasescardiovascular disease, hypertension, pulmonary disease,non-insulin dependent diabetes mellitusarthritis, certain cancers (breast, uterus, and colon),varicose veins, and gallbladder disease.