Carbohydrate Chemistry Lecture 2

Carbohydrate Chemistry Lecture 2

• 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

• 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

• 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

• 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

• 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

• 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.

Inulin

• Inulin is a polymer of fructose units.
• It's stored in plant tubers like onions and garlic.

Pectin

• 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

• 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.