lecture 2

Carbohydrates Overview

Definition

  • Carbohydrates are organic compounds containing Carbon (C), Hydrogen (H), and Oxygen (O) – referred to as "Carbon-Hydrate".

  • They include polyhydroxy aldehydes or ketones, or compounds that yield them upon hydrolysis.

  • The general formula for monosaccharides is: Cn(H2O)n or CnH2nOn (e.g., C6H12O6 = C6(H2O)6).

Functions and Importance of Carbohydrates

  1. Energy Source: Provide approximately 50% of the body's energy.

  2. Structural Components: Mucopolysaccharides, proteoglycans, and glycoproteins are key components of cell membranes and connective tissues.

  3. Nucleic Acid Structure: Phosphorylated Pentoses (Ribose-5-phosphate and Deoxyribose-5-phosphate) are vital in the structures of nucleosides, nucleotides, and nucleic acids (RNA & DNA).

  4. Digestive Health: Non-digestible carbohydrates like cellulose aid in stool bulk and intestinal movement (peristalsis), preventing constipation.

  5. Natural Anticoagulant: Heparin functions as an important natural anticoagulant.

Classification of Carbohydrates

Monosaccharides

  • Simple sugars that cannot be hydrolyzed further.

  • Classified by the number of carbon atoms and functional groups (aldehydes or ketones).

    • Trioses: 3 carbon atoms (C3H6O3)

    • Tetroses: 4 carbon atoms

    • Pentoses: 5 carbon atoms

    • Hexoses: 6 carbon atoms

    • Heptoses: 7 carbon atoms

Oligosaccharides

  • Composed of 2 to 10 monosaccharide residues linked covalently.

Polysaccharides

  • Polymers made of more than 10 monosaccharide units.

  • Includes starch, glycogen, and cellulose.

Types of Carbohydrates

Monosaccharides

  • Examples: Glucose, Fructose, Galactose

Disaccharides

  • Formed from two monosaccharide units linked by an O-glycosidic bond.

  • Examples: Sucrose, Lactose, Maltose

Polysaccharides

  • Storage Polysaccharides: Starch and Glycogen act as energy reserves.

  • Structural Polysaccharides: Cellulose provides rigidity and strength to cell walls.

Monosaccharides

Properties

  • Soluble in water and exhibit optical activity.

  • Exist in α and β forms.

Examples of Monosaccharides

  • Aldoses: Glucose, Galactose

  • Ketoses: Fructose

Disaccharides

  • Formed by the linkage of two monosaccharides via glycosidic bonds.

  • General formula: Cn(H2O)n-1.

  • Examples:

    • Maltose: Composed of two α-D-glucose units, linked by an α(1→4) bond.

    • Sucrose: Composed of α-glucose and β-fructose.

    • Lactose: Composed of galactose and glucose.

Polysaccharides

Types

  1. Storage Polysaccharides: Starch and Glycogen serve as energy reserves.

  2. Structural Polysaccharides: Cellulose provides strength to plant cell walls.

Glycogen

  • Energy storage in animals, stored in liver and muscle as granules.

  • Similar to amylopectin but with more α(1→6) branches (every 8-12 units).

Cellulose

  • Most abundant polysaccharide, providing structural support to plant cells via β(1→4) glycosidic linkages.

Starch

  • Composed of amylose (straight-chain) and amylopectin (branched).

  • Amylose is soluble in water whereas amylopectin is not.

Glycosaminoglycans (GAGs)

  • Long unbranched polysaccharides that bind water, forming a gel-like matrix in the body.

  • Examples include hyaluronic acid and chondroitin sulfate.

Glycoproteins

  • Proteins covalently bonded to carbohydrates with various biological functions including cell recognition and blood clotting.