Chapter 2: Biological Molecules

Section 2.2: Carbohydrates and Lipids

Carbohydrates

Structures of Carbohydrates

• Alpha Glucose vs Beta Glucose
  • Mnemonic: "Alpha is below, Beta is above" (referring to the position of the OH group on carbon 1).
  • Alpha Glucose: OH is below the plane.
  • Beta Glucose: OH is above the plane.

Monomers and Polymers

• Monomers: Simple molecules (e.g., glucose).
• Polymers: Complex molecules formed by joining monomers via covalent bonds (e.g., glycogen, starch).
• Glycosidic Bonds: Bonds formed between glucose units in polysaccharides.

Macromolecules

• Proteins: Composed of amino acids.
• Polysaccharides: Made from alpha and beta glucose.
• Nucleic Acids: Composed of nucleotides (DNA and RNA).

Polysaccharides

• Glycogen: Comprised of alpha glucose, highly branched.
• Starch: Consists of two components:
  • Amylose: Unbranched, composed of 1-4 glycosidic bonds.
  • Amylopectin: Branched, contains both 1-4 and 1-6 glycosidic bonds.
• Cellulose: Made from beta glucose, structural, forms straight chains with alternating glucose orientation (180-degree flip).

Monosaccharides and Disaccharides

• Monosaccharides: General formula (CH2O)n.
• Disaccharides: Formed from two monosaccharides, e.g., sucrose (glucose + fructose), maltose (glucose + glucose).

Reducing vs Non-Reducing Sugars

• Reducing Sugars: Glucose, fructose, and maltose (test positive with Benedict's solution).
• Non-Reducing Sugars: Sucrose (test negative with Benedict's solution).

Glycosidic Bonds

• 1-4 Glycosidic Bond: Common in amylose and maltose.
• 1-6 Glycosidic Bond: Present in amylopectin and glycogen (causes branching).
• Condensation and Hydrolysis
  • Condensation: Formation of glycosidic bonds with removal of water.
  • Hydrolysis: Breaking of glycosidic bonds with addition of water.

Importance of Structure

• Starch: Made of amylose (unbranched) and amylopectin (branched), varying compositions in different plants.
• Glycogen: Highly branched, stored energy form in animals.
• Cellulose: Structural component in plant cell walls, strong due to hydrogen bonds and microfibril formation.

Comparisons

• Starch vs Cellulose
  • Amylose (Starch) has 1-4 linkages, cellulose has 1-4 linkages with 180-degree rotation between glucose units.
• Starch vs Glycogen
  • Starch is part amylose (unbranched) and part amylopectin (branched), glycogen is fully branched like amylopectin but with more frequent branching.

Summary

• Chapter covers carbohydrates extensively, focusing on structural differences and their biological significance.
• Next lesson will cover lipids and proteins.