CHAPTER 5Monosaccharides Vary in StructureSlide 3Slide 4Slide 5Summary of Monosaccharide StructureThe Structure of PolysaccharidesGlycosidic LinkagesSlide 9Types of PolysaccharidesSlide 11Slide 12Slide 13How Do Carbohydrates Provide Structure?Carbohydrates and Chemical EvolutionWhat Do Carbohydrates Do?Glycoproteins: Cell IdentitySlide 18Carbohydrates and Energy StorageSlide 20Slide 21Starch and Glycogen Are Hydrolyzed to Release GlucoseEnergy Stored in Glucose Is Transferred to ATPHow Do Carbohydrates Store Energy?Key Concepts© 2011 Pearson Education, Inc.CHAPTER 5© 2011 Pearson Education, Inc.Monosaccharides Vary in Structure•Monosaccharide monomers are simple sugars that structurally vary in four primary ways:1. Location of the carbonyl group–Aldose: found at the end of the monosaccharide–Ketose: found in the middle of the monosaccharide2. Number of carbon atoms present–Triose: three–Pentose: five–Hexose: six3. Spatial arrangement of their atoms–Different arrangement of the hydroxyl groups 4. Linear and alternative ring forms–Sugars tend to form ring structures in aqueous solutions.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Summary of Monosaccharide StructureMany distinct monosaccharides exist because so many aspects of their structure are variable: aldose or ketose placement of the carbonyl group, variation in carbon number, different arrangements of hydroxyl groups in space, and alternative ring forms. Each monosaccharide has a unique structure and function.© 2011 Pearson Education, Inc.The Structure of Polysaccharides •Polysaccharides, or complex carbohydrates, are polymers of monosaccharide monomers.•The simplest polysaccharides are disaccharides, comprised of two monosaccharide monomers.–The monomers can be identical or different.Simple sugars polymerize when a condensation reaction occurs between two hydroxyl groups, resulting in a covalent bond called a glycosidic linkage.© 2011 Pearson Education, Inc.Glycosidic Linkages•The glycosidic linkages can form between any two hydroxyl groups; thus, the location and geometry of these bonds vary widely.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Types of Polysaccharides1. Plants store sugar as starch.–Mixture of branched (amylopectin) and unbranched (amylose) -glucose polymer2. Animals store sugar as glycogen.–Highly branched -glucose polymer3. Cellulose is a structural polymer found in plant cell walls.–Polymer of -glucose monomers4. Chitin is a structural polymer found in fungi cell walls, some algae, and many animal exoskeletons.–Comprised of N-acetylglucosamine (NAc) monomers5. Bacterial cell walls get structural support from peptidoglycan.–Backbones of alternating monosaccharides© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.How Do Carbohydrates Provide Structure?•Cellulose, chitin, and peptidoglycan form long strands with bonds between adjacent strands. •These strands may then be organized into fibers or layered in sheets to give cells and organisms great strength and elasticity.•Unlike the α-glycosidic linkages in the storage polysaccharides, the β-1,4-glycosidic linkages of structural carbohydrates are very difficult to hydrolyze – very few enzymes have active sites that accommodate their geometry or have the reactive groups necessary.file:///Users/ericarowe/Documents/UTK%20Biology/UTK%20Bio140%20Fall%202011/Chapter_05/A_PowerPoint_Lecture_Tools/05_Lecture_Outline/CarbohydrateStructandFunc.html© 2011 Pearson Education, Inc.Carbohydrates and Chemical Evolution•Most monosaccharides are readily synthesized under conditions that mimic early conditions; thus, it is likely that the prebiotic soup contained a wide diversity of monosaccharides.•Polysaccharides, however, despite their current relative abundance on Earth, probably played little to no role in the origin of life.–Monosaccharide polymerization requires specialized enzymes.–Polysaccharides do not catalyze any known reactions.–Polysaccharide monomers cannot provide the information required for themselves to be copied.© 2011 Pearson Education, Inc.What Do Carbohydrates Do? Carbohydrates have diverse functions in cells: In addition to serving as precursors to larger molecules, they provide fibrous structural materials, indicate cell identity, and store chemical energy.© 2011 Pearson Education, Inc.Glycoproteins: Cell Identity •Although polysaccharides are unable to store information, they do display information on the outer surface of cells in the form of glycoproteins – proteins joined to carbohydrates by covalent bonds.•Glycoproteins are key molecules in cell-cell recognition and cell-cell signaling.•Each cell in your body has glycoproteins on its surface that identify it as part of your body.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Carbohydrates and Energy Storage •Carbohydrates store and provide chemical energy in cells. •In chemical evolution, the kinetic energy of sunlight and heat were converted into chemical energy stored in the bonds of H2CO and HCN.–Today, most sugars are produced via photosynthesis, a key process that transforms the energy of sunlight into the chemical energy of C–H bonds in carbohydrates.•Carbohydrates have more free energy than CO2 because the electrons in C–H bonds and C–C bonds are shared more equally and held less tightly than they are in C–O bonds.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.Starch and Glycogen Are Hydrolyzed to Release Glucose•The hydrolysis of -glycosidic linkages in glycogen is catalyzed by the enzyme phosphorylase.–Most animal cells contain phosphorylase so they can readily break down glycogen to provide glucose.•The -glycosidic linkages in starch are hydrolyzed by amylase enzymes.–Amylases play a key role in carbohydrate digestion.© 2011 Pearson Education, Inc.Energy Stored in Glucose Is Transferred to ATP•When a cell needs energy, carbohydrates participate in exergonic reactions that synthesize adenosine triphosphate (ATP): CH2O + O2 + ADP + Pi  CO2 + H2O + ATP •The free energy in ATP is used to drive endergonic reactions and perform cell work.•Carbohydrates contain a large number of C–H bonds, which have high free energy. •Fatty acids have