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Macromolecules Atoms Molecules Macromolecules A few common macromolecules in biology are POLYMERS of a particular class of molecule. Monomers Polymers POLYMERS Biological polymers are formed by a common reaction known as CONDENSATION or DEHYDRATION (dehydration synthesis). CONDENSATION or DEHYDRATION (dehydration synthesis). Water is removed (dehydration) to form a bond between the growing polymer and the next monomer subunit. Large biological polymers are broken down through the reverse reaction--HYDROLYSIS Water (H-OH) is added to break a covalent bond between subunits in a polymer. Three Major Polymers in Biology: Polysaccharides: Polymers of sugars (carbohydrates) Proteins: Polymers of amino acids Nucleic Acids: Polymers of nucleotides A Fourth Important Class of Macromolecules: Lipids: Macromolecules constructed from fatty acids & glycerol (not simple polymers of many monomers linked end-toend) POLYSACCHARIDES: Carbohydrates have the general chemical formula: (CH2O)n where "n" is greater than 3 Monosaccharides Polysaccharides two primary classes of monosaccharides: 5 carbon sugars: ribose & deoxyribose 6 carbon sugars: glucose (see Figure 3.4C): Two common forms of glucose: a &b Two common forms of glucose: a & b Differ only in the configuration of the -OH group on the no. 1 carbon (a: -OH is down, b: -OH is up) This slight difference in structure makes a huge difference in terms of biological function Polymers of monosaccharides are formed by dehydration synthesis reactions. Note: the bond formed is between two aglucose molecules. a-1,4 linkage (between the no. 1 carbon on one a-glucose molecule and the no. 4 carbon on the other) Polymers of monosaccharides Compare the structure of an a1,4 linkage to a b-1,4 linkage Note the difference in structure, which results in differences in function Polymers of a-1,4 linkages: Starch (plants) Glycogen (animals) Polymers of b-1,4 linkages: Cellulose (plant cell walls, wood) Chitin (exoskeleton of lobsters, insects) Biological Importance: Most organisms CAN digest a-1,4 linkages to extract carbon and energy from polysaccharides Most organisms CANNOT digest b-1,4 linkages