Carbohydrates

CARBOHYDRATES

Introduction

  • Macromolecules: Large, complex molecules essential for biological functions.

  • Polymers: Many macromolecules are polymers, which are chains of smaller molecules (monomers) linked by covalent bonds.

  • Four main types of macromolecules: Carbohydrates, lipids, proteins, and nucleic acids.

Characteristics of Carbohydrates

  • Composition: Always contain carbon (C), hydrogen (H), and oxygen (O) with a general formula of (CH2O)n.

  • Functional groups: Typically, contain a high number of hydroxyl (–OH) functional groups, and sometimes carbonyl groups, making them polar and soluble in water.

  • Function: Serve as a primary source of energy upon digestion.

Monosaccharides

  • Definition: Simple sugars; "Mono" means one, "saccharide" means sugar.

  • Examples: Glucose, galactose, and fructose.

  • Isomers: All are isomers with the same molecular formula (C6H12O6) but different structural arrangements.

Alpha (α) and Beta (β) Links

  • Formation: The position of the hydroxyl group on carbon 1 determines the type of linkage during glucose formation in photosynthesis.

  • Structure: Glucose forms a linear structure initially, and upon ring formation, the –OH group may be positioned either above (β) or below (α) the carbon ring.

Disaccharides

  • Definition: Formed by the joining of two monosaccharides via a covalent bond known as a glycosidic linkage.

  • Examples:

    • Glucose + Fructose → Sucrose

    • Glucose + Galactose → Lactose

    • Glucose + Glucose → Maltose

Dehydration Synthesis of a Disaccharide

  • Process: Two glucose molecules undergo dehydration synthesis to form maltose.

  • Bond formation: The bond formed is known as a glycosidic bond with the structure C-O-C.

Polysaccharides

  • Definition: Multiple monosaccharides joined together by glycosidic linkages.

  • Examples:

    • Starch: Produced by plants; digested by the enzyme amylase.

    • Cellulose: Provides structural support to plants and adds dietary fiber.

Polysaccharides (continued)

  • Glycogen: An energy storage polysaccharide in animals.

  • Function: Liver cells synthesize glycogen post-meal to store excess glucose.

Chitin: Another Carb Example

  • Structure: Polymer composed of β-(1-4)-N-Acetyl-D-glucosamine units.

  • Enzymatic specificity: Enzymatic processing by chitobiosidase, endochitiase, and lysozyme.

DO DISSACHARIDE SKETCHES

Key Terminology from This Lesson

  • Macromolecule, Polymer, Monomer.

  • Carbohydrate.

  • Types of carbohydrates:

    • Monosaccharide, Disaccharide, Polysaccharide (with examples).

  • Reactions: Dehydration synthesis reaction, glycosidic (covalent) bond.

  • Structural types: Alpha vs. Beta glucose; Isomers