Carbohydrate Chemistry Lecture 2

Study Notes

Carbohydrates are classified as monosaccharides, disaccharides, and polysaccharides.
Monosaccharides are linked by glycosidic bonds, which can be further classified as α- or β-glycosidic bonds
Disaccharides are composed of two monosaccharides linked by a glycosidic bond.
Major disaccharides include sucrose, lactose, and maltose.
Sucrose is glucose + fructose
Lactose is galactose + glucose
Maltose is glucose + glucose
Disaccharides can be reducing or non-reducing, depending on the presence of a free carbonyl group.
Glycosidic bonds are cleaved by enzymes called glycosidases.

Polysaccharides are composed of hundreds or thousands of carbohydrate units.
Polysaccharides are not reducing sugars because the anomeric carbons are connected via glycosidic linkages.
Homopolysaccharides are composed of one type of monosaccharide.
Heteropolysaccharides are composed of more than one type of monosaccharide.

Starch is a polymer of glucose units used as a storage compound in plants.
Starch is typically insoluble in water but forms colloidal suspensions.
Starch is composed of two components: amylose and amylopectin.
Amylose is a straight-chain structure formed by α-1,4-glycosidic bonds between α-D-glucose molecules.
Amylose forms a blue color on reaction with iodine.
Amylose is poorly soluble in water but forms micellar suspensions.
Amylopectin is a branched structure formed by α-1,4-glycosidic bonds and α-1,6-glycosidic branches between α-D-glucose molecules.
Amylopectin forms a red-violet color on reaction with iodine.

Glycogen is an animal storage polysaccharide.
Glycogen structure is similar to amylopectin, differing only in branching frequency.
Glycogen gives a red-violet color reaction with iodine.
Glycogen branches occur every 8-12 residues.

Cellulose is a polymer of β-glucose units joined by β-(1,4) glycosidic linkages.
Cellulose forms a very rigid structure in extended straight chains that hydrogen bond to each other.
Cellulose is the most abundant organic compound on earth.
Found in plant cell walls.
Animals lack the enzymes needed to digest cellulose, but cellulose provides dietary fiber.

Chitin is a polymer of N-acetylglucosamine units joined by β-(1,4) glycosidic linkages.
Structurally similar to cellulose but contains acetamide in place of a hydroxy group.
Provides structural support for exoskeletons of insects and fungi.

Pectins are intercellular substances in young plants, especially abundant in ripe fruits.
Pectins consist of a-D-galacturonic acid, with some carboxyl groups esterified with methyl alcohol.

Mucopolysaccharides are polysaccharides composed of simple sugars and sugar derivatives, including amino sugars and uronic acids.
Hyaluronic acid is the most abundant mucopolysaccharide.
It's a straight chain polymer of D-glucuronic acid and N-acetyl-D-glucosamine (NAG) units.
Widely found in various tissues like vitreous body of the eye, umbilical cord, and synovial fluid.
Chondroitin is another mucopolysaccharide with a limited distribution.
It's similar to hyaluronic acid but contains N-acetyl-D-galactosamine.
It is a component of cartilage and cell coats.
Chondroitin sulfate and dermatan sulfate are widely distributed and structural components of cartilage, tendons, and bones.
Dermatan sulfate has L-iduronic acid in place of D-glucuronic acid in the structure.
Keratosulfate has D-galactose in place of the uronic acid component.
Heparin is a naturally occurring anticoagulant that prevents blood clots.
It's composed of uronic acid and amino sugar (glucosamine) units.