Most of the matter in plants, except water, is carbohydrate material
Carbohydrates account for 75% of dry plant material and are produced by photosynthesis
Cellulose
Structural element
Starch/glycogen
Energy reservoir
Photosynthesis
Plants produce carbohydrates using carbon dioxide, water, and solar energy
Carbohydrate oxidation provides energy
Carbohydrate storage, in the form of glycogen, provides a short-term energy reserve
Carbohydrates supply carbon atoms for the synthesis of other biochemical substances (proteins, lipids, and nucleic acids)
Carbohydrates form part of the structural framework of DNA and RNA molecules
Carbohydrates linked to lipids are structural components of cell membranes
Carbohydrates linked to proteins function in a variety of cell–cell and cell–molecule recognition processes
Empirical formula of simple carbohydrates
CnH2nOn or Cn(H2O)n (hydrate of C)
Carbohydrate
Polyhydroxy aldehyde, ketone, or a compound that produces such substances upon hydrolysis
Functional groups
Carbonyl<|>Ketone<|>Aldehyde
Types of carbohydrates
Monosaccharide
Disaccharide
Polysaccharide
Monosaccharides
Contain single polyhydroxy aldehyde or ketone unit<|>Cannot be broken down into simpler substances by hydrolysis reactions<|>Contain 3–7 C atoms<|>5 and 6 carbon species are more common<|>Pure monosaccharides - Water soluble white, crystalline solids
Disaccharides
Contain 2 monosaccharide units covalently bonded to each other<|>Crystalline and water soluble substances
Common disaccharides
Table sugar (sucrose)
Milk sugar (lactose)
Oligosaccharides
Contain three to ten monosaccharide units covalently bonded to each other<|>Usually found associated with proteins and lipids in complex molecules<|>Serve structural and regulatory functions
Polysaccharides
Contain many monosaccharide units covalently bonded<|>Number of monosaccharide units varies from a few 100 units to 50,000 units
Examples of polysaccharides
Cellulose - Paper, cotton, wood
Starch - Bread, pasta, potatoes, rice, corn, beans, and peas
Chirality
Chiral center: C atom attached to 4 different groups<|>A C atom must have four different groups attached to it in order to be a chiral center<|>Almost all monosaccharides are right handed<|>Amino acids are always left handed
Right- and left-handed baseball players cannot use the same glove (chiral) but can use the same hat (achiral)
Enantiomeric pairs have same solubility in achiral solvents like ethanol and have different solubility in chiral solvent like D-2-butanol
Classification of monosaccharides by number of carbon atoms
Triose - 3 carbon atoms
Tetrose - 4 carbon atoms
Pentoses - 5 carbon atoms
Hexoses - 6 carbon atoms
Classification of monosaccharides by functional groups
Aldoses: Monosaccharides with one aldehyde group
Ketoses: Monosaccharides with one ketone group
Aldohexose
Monosaccharide with aldehyde group and 6 C atoms
Ketopentose
Monosaccharide with ketone group and 5 C atoms
Glucose
Most abundant in nature<|>Most important source of human nutrition<|>Six-membered cyclic form
Galactose
Milk sugar<|>Synthesized in human beings<|>Part of brain and nerve tissue<|>Used to differentiate between blood types<|>Six-membered cyclic form
Fructose
Ketohexose<|>Sweetest tasting of all sugars<|>Found in many fruits and in honey<|>Good dietary sugar due to higher sweetness<|>Five-membered cyclic form
Ribose
Part of a variety of complex molecules which include RNA, ATP, and DNA<|>Five-membered cyclic form
Cyclic forms of D-Glucose
α-form where the –OH of C1 and CH2OH of C5 are on opposite sides<|>β-form where the –OH of C1 and CH2OH of C5 are on the same side
Glycosidic linkage
Formed when two monosaccharides react to form a disaccharide
Maltose (Malt Sugar)
Structurally made of 2 D-glucose units, one of which must be α-D-glucose, linked via an α(1→4) glycosidic linkage<|>Digested easily by humans because of an enzyme that can break α(1→4) linkages
Cellobiose
Produced as an intermediate in the hydrolysis of the polysaccharide cellulose<|>Contains two D-glucose monosaccharide units, one of which must have a β configuration, linked through a β(1→4) glycosidic linkage<|>Cannot be digested by humans
Lactose
Made up of β-D-galactose unit and a D-glucose unit joined by a β(1→4) glycosidic linkage<|>Milk is rich in the disaccharide lactose<|>Lactase hydrolyzes β(1→4) glycosidic linkages