Chapter 5 Carbohydrates How is Energy Stored in Carbohydrates Carbohydrates Term for monosaccharides disaccharides and polysaccharides Chemical formula is They are molecules with a carbonyl C O and several OH functional groups along with many C H bonds Key Concepts Sugars and other carbohydrates are highly variable in structure are monomers that polymerize to form polymers called polysaccharides and are joined by different types of Carbohydrates perform a wide variety of functions in cells serving as raw material for synthesizing other molecules providing structural support indicating cell identity and storing chemical energy Review Triose Pentose Hexose 3 ways simple sugars monosaccharides differ from each other 1 Location of 2 Number of 3 Spatial arrangement of atoms especially the position of the Polysaccharides Polysaccharides or complex carbohydrates are polymers of monosaccharide monomers The simplest polysaccharides are comprised of two monosaccharide monomers The monomers can be identical or different Simple sugars polymerize when a reaction occurs between two hydroxyl groups resulting in a covalent bond called a glycosidic linkage Glycosidic Linkages The hydroxyl groups from the 1 carbon and the 4 carbon react to produce an 1 4 glycosidic linkage and water Glycosidic Linkages The glycosidic linkages can form between any two hydroxyl groups thus the location and geometry of these bonds vary widely Biologically Relevant Polysaccharides 1 Plants store sugar as Mixture of branched amylopectin and unbranched amylose glucose polymer 2 Animals store sugar as Highly branched glucose polymer 3 is a structural polymer found in plant cell walls Polymer of glucose monomers 4 is a structural polymer found in fungi cell walls some algae and many animal exoskeletons Comprised of N acetylglucosamine NAc monomers 5 Bacterial cell walls get structural support from Backbones of alternating monosaccharides 1 Plants store sugar as starch Mixture of branched amylopectin and unbranched amylose glucose polymer 2 Animals store sugar as glycogen Highly branched glucose polymer 3 Cellulose is a structural polymer found in plant cell walls Polymer of glucose monomers 4 Chitin is a structural polymer found in fungi cell walls some algae and many animal exoskeletons Comprised of N acetylglucosamine NAc monomers 5 Bacterial cell walls get structural support from peptidoglycan Backbones of alternating monosaccharides Carbohydrate Function Carbohydrates as Structural Molecules Cellulose Chitin Peptidoglycan Form Tough Fibers Cellulose in plant cell wall Chitin in insect exoskeleton Peptidoglycan in bacterial cell wall Glycoproteins Cell Identity Although polysaccharides are unable to information they do 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 Cell Identity don t store information but display it Carbohydrates and Energy Storage Carbohydrates store and provide in cells 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 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 even more C H bonds and consequently more free energy than carbohydrates
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