Carbohydrates

• Carbohydrates are the most abundant of the four macromolecules, with purposes ranging from energy storage to structural components.
• The general form of carbohydrates is CH2O.
• Carbohydrates are also called “saccharides” which means “sugars”.
• Carbohydrates such as glucose are produced by photosynthesis in plants.
• Monosaccharides are the simplest carbohydrates, containing several hydroxyl groups attached to a chain of three to eight carbon atoms (except at the carbonyl carbon).
• Aldoses are monosaccharides that contain an aldehyde group.
• Ketoses are monosaccharides that contain a ketone group.
• D-glucose, D-galactose, and D-fructose are the most important monosaccharides; all hexoses with formula C6H12O6 (isomers).
• D-glucose is the most common hexose, also known as dextrose and blood sugar in the body.
• D-glucose is found in fruits, vegetables, corn syrup, and honey.
• D-glucose is the building block of sucrose and lactose as well as cellulose and glycogen.
• D-galactose is an aldohexose found in milk and is important in the cellular membranes of the brain and nervous system.
• D-fructose is a ketohexose that is the sweetest of the carbohydrates, twice as sweet as sucrose.
• The aldehyde group in monosaccharides can be oxidized to a carboxylic acid by an oxidizing agent such as Benedict’s solution.
• Monosaccharides are converted into sugar acids through the oxidation of the aldehyde, with Cu2+ being reduced to Cu+
• Monosaccharides can form reducing sugars, which are carbohydrates that reduce another substance.
• Fructose usually cannot be oxidized unless in a basic Benedict’s solution, and when oxidized, it becomes glucose.
• Reduction converts an aldehyde group to alcohol.
• Sugar alcohols, also known as alditols, are used as sweeteners in many sugar-free products such as D-sorbitol, D-xylitol, and D-mannitol.
• Disaccharides are formed when two monosaccharides combine in a dehydration reaction and are linked by a glycosidic bond.
• Maltose, also known as malt sugar, is obtained from hydrolysis of starch and is used in cereals, candies, and brewing.
• Lactose, found in milk and milk products, consists of B-D-galactose and a- or b-D-glucose.
• Sucrose, or table sugar, consists of a-D-glucose and b-D-fructose and cannot form an open chain or be oxidized; it is not a reducing sugar.
• Polysaccharides are three or more monosaccharides and include amylose & amylopectin (forming starch), cellulose, and glycogen.
• Starch is the form of glucose in plants and is insoluble in water, hydrolyzing in water to give smaller saccharides called dextrins, maltose, and glucose.
• Amylose, 20% of starch, is a helical coil.
• Amylopectin, 80% of starch, is a branched-chain polysaccharide and is complex carbohydrates within the body, digested by enzymes in saliva and maltase in intestines.
• Glycogen is an animal starch, a polymer of glucose stored in the liver and muscles of animals, and is more highly branched than amylopectin.
• Cellulose is the major structural unit of wood and plants and cannot form hydrogen bonds in water, giving a rigid structure to cell walls in wood and fiber.
• Stereoisomers are molecules with the same formula but different structure.
• Enantiomers are chiral stereoisomers.
• Fischer Projection is a two-dimensional representation of a molecule, with the most oxidized group at the top, vertical lines for bonds that go back, horizontal lines for bonds that go forward, chiral carbon in the middle, L- if OH is on the left and D- if it is on the right, and counting is based on chiral carbon farthest from C=O group.
• Chiral means nonsuperimposable; there are 4 different groups bonded to a carbon.
• Achiral means superimposable; at least 2 groups are the same.