🍞 Carbohydrates

Overview

Carbohydrates: Carbon (C), Hydrogen (H), Oxygen (O) in 1:2:1 ratio → (CH₂O)ₙ

Functions:

1. Energy storage (starch, glycogen)
2. Structural support (cellulose, chitin)
3. Cell recognition
4. Energy currency (glucose)

Types of Carbohydrates

1. Monosaccharides (Simple Sugars)

• Glucose (C₆H₁₂O₆): Primary energy source
• Fructose: Fruit sugar
• Galactose: Component of lactose
• Ribose/Deoxyribose: RNA/DNA components

2. Disaccharides

Formed by dehydration synthesis (removes H₂O):

• Maltose = Glucose + Glucose
• Sucrose = Glucose + Fructose
• Lactose = Glucose + Galactose

Broken by hydrolysis (adds H₂O)

3. Polysaccharides

Storage:

• Starch (plants): α-glucose polymer, stored in plastids
• Glycogen (animals): highly branched α-glucose, liver/muscle

Structural:

• Cellulose (plants): β-glucose polymer, cell walls
  • Most abundant organic polymer on Earth
  • Humans cannot digest (lack cellulase)
• Chitin: Modified glucose with N-groups
  • Fungal cell walls, arthropod exoskeletons

Key Concepts

α-glucose vs. β-glucose:

• α: OH on C1 below ring → forms starch/glycogen (digestible)
• β: OH on C1 above ring → forms cellulose (indigestible)

Glycosidic bonds:

• Formed by dehydration synthesis
• Broken by hydrolysis
• Enzyme specificity determines digestibility