Chapter 20: Carbohydrates. Carbohydrate: A polyhydroxyaldehyde or polyhydroxyketone , or a substance that gives these compounds on hydrolysis. Chapter Overview: Monosaccharides Fischer projections Haworth projections Hemiacetals and Acetals Oxidation and reduction Disaccharides
Carbohydrate: A polyhydroxyaldehyde or polyhydroxyketone, or a substance that gives these compounds on hydrolysis.
Monosaccharide:A carbohydrate that cannot be hydrolyzed to a simpler carbohydrate.
( ____________ )
Fischer projection:A two-dimensional representation for showing the configuration of tetrahedral stereocenters.
In 1891, Emil Fischer made the arbitrary assignments of D- and L- to the enantiomers of glyceraldehyde.
The most common monosaccharides:
The prefix “deoxy” means “without oxygen.”
Fructose is a ketose and it also forms cyclic hemiacetals
Hemiacetal + Alcohol = Acetal
Disaccharide: a carbohydrate containing two monosaccharide units joined by a glycosidic bond.
Sucrose (table sugar) = Glucose + Fructose
Lactose = Galactose + Glucose
Maltose = Glucose + Glucose
Monosaccharides are colorless crystalline solids, very soluble in water, but only slightly soluble in ethanol.
Sweetness relative to sucrose:
Polysaccharide: A carbohydrate consisting of large numbers of monosaccharide units joined by glycosidic bonds.
Starch: A polymer of D-glucose.
Amylopectin, a branched polymer of approximately 10,000 units of D-glucose joined by -1,4-glycosidic bonds.
Glycogen is the energy-reserve carbohydrate for animals.
Cellulose is a linear polysaccharide of D-glucose units joined by β-1,4-glycosidic bonds.
Cellulose is a linear polymer containing as many as 3000 units of D-glucose joined by β-1,4-glycosidic bonds.