Microbial Metabolism(Chapter 5)Lecture MaterialsforAmy Warenda Czura, Ph.D.Suffolk County Community CollegeEastern CampusPrimary Source for figures and content:Tortora, G.J. Microbiology An Introduction 8th, 9th, 10th ed. San Francisco: PearsonBenjamin Cummings, 2004, 2007, 2010.Amy Warenda Czura, Ph.D.1SCCC BIO244 Chapter 5 Lecture SlidesMetabolism = sum of all chemical reactions ina living organism:- Catabolic reactions: break complex organiccompounds into simper ones, usually via hydrolysis, usually exergonic- Anabolic reactions: build complex moleculesfrom simpler ones, usually via dehydrationsynthesis, usually endergonic*Catabolic reactions provide the energy (ATP)and building blocks to drive anabolic reactions (cell growth and repair)(handout)Amy Warenda Czura, Ph.D.2SCCC BIO244 Chapter 5 Lecture SlidesMetabolic pathway = series of steps to perform a chemical reaction in living organisms, requires a new enzyme at eachstepPathways used by an organism depend onenzymes encoded by the DNA: what typesof reactions any one organism can performis determined by its genetic makeupEnzymes- biological catalysts, catalytic proteins- speed up reactions by lowering activationenergy, orient molecules to favor reactionAmy Warenda Czura, Ph.D.3SCCC BIO244 Chapter 5 Lecture Slides- can increase reaction rates up to 10 billion Xfaster than random collisions allowTurnover number = maximum number of substrate molecules an enzyme converts toproduct each second,different for different enzymesEach enzyme has a unique 3D shape: it will bind only its specific substrate(s) at the active site and catalyze only one specific reaction resulting in particular product(s)All cellular reactions performed by enzymes:cells require thousands of different enzymesall encoded by the DNA to carry out all reactions required for lifeThe majority of proteins in a cell are enzymesAmy Warenda Czura, Ph.D.4SCCC BIO244 Chapter 5 Lecture SlidesEnzyme Nomenclature-most end in - “ase”-6 classes based on type of reaction:1. Oxidoreductaseoxidation/reduction reactions2. Transferasetransfer functional groups3. Hydrolasehydrolysis4. Lyaseremoval of atoms without hydrolysis5. Isomeraserearrangement of atoms in a molecule6. Ligasejoining of two molecules- typically named for reaction catalyzed and substrate acted upon:e.g. DNA ligase: functions to join two piecesof DNA togetherAmy Warenda Czura, Ph.D.5SCCC BIO244 Chapter 5 Lecture SlidesEnzyme Components:Most enzymes have two parts:1. Apoenzyme = protein part, inactive by itself2. Cofactor = non-protein part, usually a metal ion, turns the apoenzyme onCoenzyme = organic cofactorapoenzyme + ‘cofactor’ = holoenzyme (whole active enzyme)Metal ion cofactors form a bridge between enzyme and substrate to facilitate the reactionCoenzymes accept/donate atoms or carry electrons to transfer to other moleculesAmy Warenda Czura, Ph.D.6SCCC BIO244 Chapter 5 Lecture SlidesTwo most important coenzymes:- NAD+(nicotinamide adenine dinucleotide) Carries electrons in catabolic reactions- NADP+(nicotinamide adenine dinucleotide phosphate) Carries electrons in anabolic reactionsBoth are derived from the B vitamin nicotinicacidAmy Warenda Czura, Ph.D.7SCCC BIO244 Chapter 5 Lecture SlidesMechanism of Enzyme Action(on handout)1. The substrate contacts the active site2. The enzyme-substrate complex is formed.3. The substrate molecule is alteredatoms are rearranged,or the substrate is broken into smaller parts,or the substrate is combined with another molecule4. Product(s) is/are released from the active site.5. The enzyme is unchanged and can catalyze a new reaction.Each enzyme acts on only one substrate, but any one substrate can be acted upon by multiple enzymesAmy Warenda Czura, Ph.D.8SCCC BIO244 Chapter 5 Lecture SlidesEnzymes must be controlled to maintain homeostasis: two ways to control:1. level of synthesis (amount produced)2. level of activity (control cofactors, restrictaccess to substrate)Factors that influence enzyme activity:1. Temperature↑ temp = ↑ reaction rateuntil denaturation-Enzymes have an optimaltemperature = temp atwhich the enzymecatalyzes the reaction atits maximum rate-above this they become denatureddenatured = unfolded, enzyme no longer fitssubstrate, cannot catalyze the reactionAmy Warenda Czura, Ph.D.9SCCC BIO244 Chapter 5 Lecture Slides2. pH-enzymes have an optimalpH that favors the nativeconformation (correctfolding)-pH that is too acidic or toobasic will denature the enzyme3. Substrate concentration↑ substrate conc = ↑ rxn rateuntil saturation-each enzyme has amaximum turnovernumber = top speed forconverting substrate intoproduct-at saturation, the active site is always full: theenzyme works at maximum speed-addition of more substrate beyond the saturation point will not increase the reaction ratesaturationAmy Warenda Czura, Ph.D.10SCCC BIO244 Chapter 5 Lecture Slides4. Inhibitorsinhibitor = a substance thatblocks enzyme functionThree types:A. Competitive inhibitors-block the active site-same shape as the substrate-competes for the active sitethus blocking enzymereaction with the substrate-some bind permanently thus killing the enzyme =irreversible competitive inhibitor-some bind reversibly and justslow the reaction rate =reversible competitive inhibitorB. Noncompetitive inhibitors-does not bind the active site-binds elsewhere= the allosteric siteAmy Warenda Czura, Ph.D.11SCCC BIO244 Chapter 5 Lecture Slides-binding of inhibitor to the allosteric site causes a shape change in the whole enzymesuch that substrate no longer fits in the active site = allosteric inhibition-a reversible allosteric inhibitor will slow thereaction rate-an irreversible allosteric inhibitor will kill theenzyme permanentlyC. Enzyme poisons-bind up metal ion cofactors thus preventing formation of the holoenzymeAmy Warenda Czura, Ph.D.12SCCC BIO244 Chapter 5 Lecture SlidesUsually there are many steps in a metabolic pathway to convert substrate to final productEach step requires a different enzymeFeedback inhibition / End product inhibition:-the product controls its own rate of formation-occurs when the finalproduct can inhibit oneof the enzymes in thepathway-when productaccumulates, thepathway is shutdown to preventover-production-common toanabolic pathways-usually functionsby reversibleallosteric inhibition of the first enzymeAmy Warenda Czura, Ph.D.13SCCC BIO244 Chapter 5 Lecture SlidesEnergy Production In A Cell(notes on typed handout)Metabolism overviewplay