Biochemistry 4: Carbohydrate Structure and Functio Carbohydrate Classification Nomenclature: 3 carbons: Trioses, 4 carbons: Tetroses, etc. Some common names: glucose, fructose & galactose. D and L: Based on the D- and L- forms of glyceraldehyde. Look at the highest numbered chiral carbon, -OH on right = Dsugars, -OH on left = L-sugars. Nearly all carbohydrates in nature are in the D-configuration. Compared to amino acids, which are found in the L-confiduration. Enantiomers: Stereoisomers that are non-superimposable mirror images of each other. D and L forms of the same sugar. Diastereomers: Any stereoisomer that is not an enantiomer. Epimers: Subtype of diastereomers that differ at exactly one chiral carbon. Anomers: A subtype of epimers that differ at the anomeric carbon. Monosaccharides Monosaccharides: Single carbohydrate units, with glucose as the most commonly observed monomer. Can undergo oxidation/reduction, esterification, and glycoside formation Aldoses: Oxidized into aldonic acids, reduced to alditols Sugar as Reducing Sugars that can be oxidized are reducing agents Agent: themselves. Can be detected by reacting with Tollen’s or Benedict’s reagents Deoxy Sugars: -H replaces –OH Esterification: Sugars react with carboxylic acids and their derivatives, forming esters Phosphorylation: A phosphate ester is formed by transferring a phosphate group from ATP onto the sugar. This rxn is similar to esterification Glycoside Formation: The basis for building complex carbohydrates and requires the anomeric carbon to link to another sugar Enantiomers Diastereomers Enantiomers Cyclic Sugar Molecules Complex Carbohydrates Cyclization: Describes the ring formation of carbohydrates from their straight-chain forms. Anomeric Carbon: The new chiral center formed in ring closure; it was the carbon containing the carbonyl in the straight-chain form. Disaccharides: Form as a result of glycosidic bonding between two monosaccharide subunits. Common examples: sucrose, lactose, maltose. Polysaccharides: Formed by repeated monosaccharide or polysaccharide glycosidic bonding. a -anomers: Have the –OH on the anomeric carbon trans to the free –CH2OH group. Cellulose: The main structural component for plant cell walls. Main source of fiber in human diet. b-anomers: Have the –OH on the anomeric carbon cis to the free – CH2OH group. Starches: Main energy storage form for plants. Amylose: Unbranched Amylopectin: Branched Haworth Represent 3D structure of a monosaccharide. Projections: Mutarotation: Spontaneous shift from one anomeric form to another with the straight-chain form as an intermediate. Maltose: (glucose + glucose with alpha glycosidic bond) Lactose: (galactose + glucose with beta glycosidic bond) b-D-Glucose a -D-Fructose Examples of Cyclic Sugar Molecules Sucrose: (glucose + fructose with alpha glycosidic bond)