1MetabolismPart I: FermentationsPart II: RespirationLearning objectives are to gain anappreciation of:• Catabolism and anabolism• ATP Generation and energyconservation• Fermentation2Importance of MetabolismImages: (1) www.bact.wisc.edu (2) en.wikipedia.org• Industrial– Yogurt, cheese– Bread, wine, beer• Medical/Health– Strain identification– Digestion• Environmental– Cycling of elements– Pollutant transformationMetabolism: the bigger picture• What is metabolism?– Chemical reactions that occur in livingorganisms in order to maintain life.• What does “maintain life” mean?– Growth and division– Maintaining cellular structures– Sense/respond to environment• Two parts of metabolism:–3Cell componentsnutrients + C-source chemicals or lightTwo parts of metabolism• Anabolism- synthesis of complex moleculesfrom simpler ones during which energy isadded as input• Catabolism- the breakdown of larger,more complex molecules into smaller,simpler ones, during which energy isreleased, trapped, and made available forwork4Anabolism and Growth• Appropriate nutrients:– Carbon source– N, S, P sources– Trace metals• Appropriate environmental conditions:– pH– Oxygen– Temperature.– LightCO2AutotrophOrganic CompoundsHeterotrophAnabolism(biosynthesis)Carbons Sources5CatabolismOrganotrophsPhototrophsLitotrophsChemotrophsOrganic compounds,i.e., glucose, succinateInorganic compounds,S, Fe2+,CO2, H2, CH4LightChemical compoundsATP, pmfEnergy Sources:• Adenosine triphosphate• two of the phosphatebonds are high energybonds• breaking bond toremove phosphatereleases energyFigure 5.6ATP and Energy6The Role of ATP in Metabolism• Reactions in which the terminal phosphate of ATP isremoved results in a:• Exergonic breakdown of ATP can be coupled with:• Energy conserving reactions are used to catalyzethe formation of ATP from ADP and Pi, and thus torestore the energy balance of the cellATP is produced by three processes:• _________________ phosphorylation– Two reactions are coupled to make ATP.• __________________ phosphorylation– Carried out by:– Requires:• Photophosphorylation7Chemical-based ATP synthesis:Substrate level phosphorylationRespiration-linked phosphorylationADP obtains phosphate frommetabolic intermediate• molecule which has a highenergy bondATP is formedATP synthesis by substrate-levelphosphorylation• Phosphorylated intermediates are generated in:– Glycolysis (Embden-Meyhof pathway)– Tricarboxylic Acid Cycle (TCA)– Fermentation• Finally, the Pi is transferred from a high energyphosphorylated intermediate to ADP by a kinase8Embden Meyerhof Pathwaya.k.a. glycolysis• Major pathway for:• Major pathway of:• Widespread method of:• The end result is the release of a small amount ofenergy– conserved as ATP through:– And fermentation end products.Glycolysis and Fermentation• Glycolysis is an anoxic process• It is divided into two major stages• Nets two ATPs and two NADHs• End product of glycolysis is:• The fate of this metabolite varies:9Energy InputReductionsATP by SLPGlucose + 6O2 6CO2 + 6H2O ∆G˚’= -2830 kJ/mol10Glycolysis and NADH• Glycolysis also generates NADH• But, cells need:• Fermentation can regenerate:– This can be done through:– Substrates can be reduced by NADHExample:Lactic acidfermentationNADH11FermentationATP production by substratelevel phosphorylationWhat is fermentation?• Widespread method of anaerobic metabolism• The end result is the release of a small amount ofenergy– conserved as ATP through substrate levelphosphorylation• Incomplete oxidation of substrates• Need to have a fermentation balance– Oxidation-reduction state of products equal thesubstrates– NAD+ recycled• Fermentation end products are generally secreted12Why is fermentation important?• Ecologically important for decompositionof organic material in anaerobicenvironments• Byproducts are usually energy rich andused by other microbes as energy/carbonsources• Useful in food industry• DigestionLots offermentablecarbon sourcesSubstrate level P13Lactic Acid Fermentation: I• Carried out by several groups ofbacteria–Lactobacillus and Lactococcus• Gram +• No cytochromes• Anaerobes• Only use sugarsLactic AcidFermentationKey ReactionFermentations haveto maintain redoxbalance.14Lactic acid bacteria and dairyproducts• These bacteria are used to to makecheese and yogurt from milk.• Carbon/energy source in milk is lactose• Lactose is hydrolyzed• Causes pH to decrease• Milk proteins coagulatehttp://web.mit.edu/esgbio/www/lm/sugars/lactose.gifhttp://www.reluctantgourmet.com/images/cheese.jpgWhat happens to the lactate?• Transported out by lactate symporter– Takes a proton out with it.• Lactate is still a good carbon/energysource.Glucose  2 Lactate ∆G˚’= -196 kJ/molMade 2 ATPs = +63 kJ/mol-133 kJ/mol left in lactateWasted energy!15Lactic acid bacteria are wastefulor are they?• They live in organic rich environmentswithout oxygen• They generate a proton gradient so moreATP can be made• They make acid which inhibits competitors• They can grow in low iron environmentsSubstrates other than glucose• Monosaccharides– Fructose, mannose, galactose getconverted to glucose-6-phosphate orfructose-6-phosphate• Disaccharides--get cleaved inmonosaccharides by specific enzymes– Lactose => galactose and glucose– Maltose => 2 glucoses– Sucrose => glucose and fructose16Large complex polysaccharides• Starch, cellulose:found in plant material• Glycogen: found inanimals• Bacterium needsspecific enzyme tobreak down the sugarchains into monomers– The enzymes are oftensecreted.Some Complex PolysaccharidesCellulo seAerobic decomposition:myxobacteriacytophagasporocytophagaFermented by:some clostridiaStarchAmylases in:Bacillus acidocaldariusStreptococcus bovisBacteroides amylophilusglucanases17Polysaccharides and Catabolic EnzymesIn many cases the sugar monomers are ultimately metabolizedeither by glycolysis or another pathway to generate pyruvate.Fermentations products are not fully oxidized∆G˚’ glucose >> 2 lactate + 2H+ = -198 kJ/mol∆G˚’ glucose + 6O2 >> 6CO2 + 6H2O = -2830 kJ/molMore energy can be conservedfrom glucose by oxidizing it to CO218Cells do this by:• Oxidative phosphorylation• The tricarboxylic acid cycleNext LectureThe maximum energy stored in glucose can beconserved only when its complete oxidation