You should read the entire chapter. For the midterm, you will not be tested on the following topics :1. kinetic details of different types of enzyme inhibition (pp. 266-268) 2. kinetic details of allosteric enzymes (pp. 280, middle of page, to 281, middle of page).3. Details of regulation by phosphorylation (pp. 282, near bottom of page, to 286, near bottom of page).4. Hexokinase and Enolase--but these will be included later, when we study glycolysisChymotrypsinChapter 8 (continued)EnzymesEnzyme Kinetics: Michaelis-Menton EquationVmax[S]Vo =____________KM + [S]KM = [S]when Vo =Vmax_____21 KM 1 ______ = _______ +______Vo Vmax[S] VmaxDouble-Reciprocal or Lineweaver-Burk PlotE + S ES E + Pk1k-1k2Vmax[S]Vo =____________KM + [S]Vmax = k2[Etotal]This is true only for this specific (rather simple) mechanism!kcator Turnover NumbersVmax = kcat[Etotal]More general:Vo =Vmax[S]_________Km + [S]=kcat[Etotal][S]_________________Km + [S]Steady-State Kinetics Can Help Determine MechanismTernary ComplexReaction Mechanism Ping-pongorDouble-Displacement Reaction MechanismsInhibitor (I) binds only to E, not to ESInhibitor (I) binds either to E and ES or to ES alone.Inhibitor (I) binds only to ES, not to E. This is a hypothetical case that has never been documented for a real enzyme, but which makes a useful contrast to competitive inhibitionEnzyme InhibitionCompetitive Uncompetitive MixedInhibition Inhibition InhibitionKmchanges while Vmaxdoes not Km and Vmaxboth changeKm and Vmaxboth changeIrreversible Inhibition(Irreversible)diisopropylfluorophosphatechymotrypsinEnzyme Activity is Affected by pHRegulatory Enzymesimportant in controlling flux through metabolic pathways2. Regulation by covalent modification1. Allosteric enzymesExample of an allosteric regulatory enzymeTwo views of aspartate transcarbamoylase•12 subunits: 6 are catalytic and six are regulatory•Regulatory subunits are shown in red and yellowRegulation by Feedback InhibitionConversion of L-threonine to L-isoleucine catalyzed by a sequence five enzymes, E1-E5L-isoleucine is an inhibitoryallosteric modulator of E12. Regulation by covalent modificationMost common2. Regulation by Covalent Modification:Proteolytic cleavage of zymogenCarbohydrates and Glycobiology (Chapter 9)Carbohydrate (sugar): hydrated carbons.Common chemical composition.C (H2O)[]nwhere n > 2 Functional roles of sugarsStructural. Polymers serve structural role (e.g. cellulose, chitanand peptidoglycan)Food storage. e.g. starch(plants) and glycogen (animals) Part of genetic material. e.g. primary component of DNA andRNA.Components of other biomolecules. Appended to proteins andlipid molecules.Monosaccharides “simple sugars”: Consist of aldehyde or ketonederivatives of polyalcohols that contain 3 or more carbons. Theycan not be hydrolyzed into simpler sugars and are the buildingblocks for more complex polysaccharides. AldosesExample:H -C -R1= OKetosesExample:R2-C -R1= OtriosesRepresentative monosaccharides,“simple sugars”single polyhydroxyaldehyde or ketone unitpentoses in DNA and RNAhexosesRepresentations of the two stereoisomers of glyceraldehydeMost sugars are chiral moleculesThe natural form of most sugars is the D-formD-aldosesD refers to configuration at chiral center most distance from carbonyl carbonyou will be responsible for knowing the structures of the sugars named in boxes. These are the most common in nature.(Marked with )D-ketosesTwo sugars that differ only in the configuration around one carbon atom are called epimersD-Glucose and two of its epimersIn aqueous solution, all common monosaccharides with five or more carbons have cyclic structuresHaworth Projections: an easier way to represent cyclic sugar structure. Draw molecule from side view with the carbons of the ring represented by lines.Haworth projections of D-Glucopyranose.Furanose and pyranose rings are not planarPyranose ringsfavoredβ-D-glucopyranoseFormation of two cyclic forms of D-glucoseAlpha form: hydroxyl group at anomeric carbonis on the opposite side as –CH2OHBeta form: hydroxyl group at anomeric Carbon is on the same side as –CH2OHPyranoses and furanosesanomersA chair conformation of Conformations are preferred that have bulky substituents in the equatorial positionsOrganisms contain a variety of hexose derivativesR =lactic acidChemistry of SugarsR-CHO=R-CO=+ H2O+ 2 H++ 2 e-Aldehydes as reducing agentsOH1.2.3.O2 + 2 H++ 2 e-H2O2+ O2 + H2O + H2O2R-CH=OOR-C=O-Sugars as reducing agents(Ketoses isomerize to aldosesunder the conditions used for these oxidation reactions with copper ions and thus also act as reducing sugars.)Disaccharides contain an O-glycosidic BondThis ring can’t open up and is no longer reducingThis ring can open up to an aldehyde and is still reducingSome common disaccharidesStarch and Glycogen are energy storage moleculesStarch granules in chloroplastAmylose and amylopectinGlycogen granules in hepatocyteStarch and GlycogenShort segment of amylose, a long, unbranched polymer of D-glucose residues in (α1→4) linkageLike amylose, amylopectin is also high mw, but it is highly branched. Above is an (α1→6) branch point of amylopectin.A cluster of amylose and amylopectin such as is shown above is believed to occur in starch granuoles.Glycogen is similar to amylopectin, but much more highly branched.The (α1→4) linkages cause the chains in starch and glycogen to curl up and make the resulting granules very dense.Two units of a cellulose rigid chain. The D-glucose residues are in the (β1→4) configuration and therefore straight.Cellulose and chitin are structural homopolysaccharidesA short segment of chitin, a homopolymer of N-actyl-D-glucosamine units in (β1→4) linkageTwo parallel cellulose chains, showing inter- and intrastrandhydrogen bonding cross-links between themBacterial Cell Walls Contain Peptidoglycans.The rigid component of bacterial cell walls is a heteropolymer of alternating (β1→4) linked N-acetylglucosamine and N-acetylmuramic acid residues.The linear polymers lie side by side in the cell wall, cross-linked by short peptides, the exact structure of which depends on the bacterial species.Peptidoglycan of the cell wall of Staphylococcus aureusPeptides (strings of colored spheres) covalently link N-acetylmuramic acid residues in a neighboring polysaccharide chains.only in gram-positive bacteriaFound in synovialfluid in jointsFound in cartilage and
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