carbohydrates - molecules w/ carbon, hydrogen, oxygen in ratio 1:2:1  

• empirical formula - (CH2O)n
• releases energy from C-H bonds when oxidized
• sugars - most important energy-storage carbohydrate

monosaccharides - simplest of the carbohydrates  

• can contain as few as 3 carbon, but most contain 6
• C6H12O6, or (CH2O)6
• usually forms rings in aqueous environments (but can form chains)
• glucose - most important energy-storing monosaccaride; has 7 C-H bonds for energy

disaccharide - "double sugar"  

• 2 monosaccharides joined by a covalent bond
• play roles in transporting sugars (so that it is less rapidly used for energy during transport)
• only special enzymes located at where glucose is to be used can break the bonds
• normal enzymes along the transport route can't break apart disaccharides
• sucrose - fructose + glucose; used by plants to transport glucose
• lactose - galactose + glucose
• maltose - glucose + glucose

polysaccharide - macromolecules made of monosaccharides  

• insoluble long polymers of monosaccharides formed by dehydration synthesis
• starch - used to store energy; consists of linked glucose molecules
• cellulose - used for structural material in plants; consists of linked glucose molecules
• amylose - simplest starch; all glucose connected in unbranched chains
• amylopectin - plant starch; branches into amylose segments
• glycogen - animal version of starch; has more branches than plant starch

sugar isomers - alternative forms of glucose  

• same empirical formula, but different atomic arrangement
• fructose - structural isomer of glucose; oxygen attached to internal carbon, not terminal; tastes sweeter than glucose
• galactose - stereoisomer of glucose; hydroxyl group oriented differently from glucose

structural carbohydrates  

• alpha form - where glucose bonds w/ the hydroxyl group below the plane of the ring
• beta form - where the glucose bonds w/ the hydroxyl group above the plane of the ring
• starch contains alpha-glucose chains
• cellulose - contains beta-glucose chains; cannot be broken down by starch-degrading enzymes; serves as structural material
• a few animals use bacteria/protists to break down cellulose
• chitin - structural material in arthropods/fungi; modified cellulose w/ nitrogen group added to glucose units