Lecture Notes: Carbohydrates

Introduction to Carbohydrates

• Carbohydrates are one of the macromolecule types discussed.
• Common sources: bread, pasta, cake, fruits (apples, pears, grapes, strawberries), grains, vegetables.
• Provide energy through glucose.
• General formula: Cn(H2O)n (e.g., glucose: C6H12O6).

Types and Structure

Subtypes of Carbohydrates

• Monosaccharides: Single sugar, chain length 3-7 carbons (e.g., glucose, sucrose).
  • Aldoses: Central carbon bound to an H.
  • Ketoses: Central carbon bound to two carbons.
  • Named based on carbon chain: triose (3), pentose (5), hexose (6).
• Disaccharides: Two sugars linked (e.g., sucrose, lactose).
• Polysaccharides: Many sugars linked, can be branched or unbranched.
• Oligosaccharides: Few sugar units (3-20), less common.

Common Monosaccharides

• Glucose: Main energy source.
• Galactose: Part of lactose.
• Fructose: Found in fruits, part of sucrose.

Structural Isomers

• Glucose, galactose, fructose are isomers (same formula, different structures).
• Monosaccharides can be linear or ring forms.
• Alpha vs. Beta sugars:
  • Alpha: Hydroxyl below C1.
  • Beta: Hydroxyl above C1.

Disaccharides and Glycosidic Bonds

• Formed by linking monosaccharides via dehydration reaction.
• Glycosidic bonds: Covalent linkages.
• Common disaccharides:
  • Maltose: Two glucose units.
  • Lactose: Galactose + glucose.
  • Sucrose: Glucose + fructose.

Polysaccharides

• Starch: Plant storage (amylose and amylopectin).
• Glycogen: Animal storage, highly branched.
• Cellulose: Plant cell walls, cannot be digested by humans.
  • Herbivores have microbes to digest cellulose.
• Chitin: Found in exoskeletons and fungal walls.

Starch and Glycogen

• Amylose: Unbranched, alpha 1-4 linkages.
• Amylopectin: Branched, alpha 1-4 and alpha 1-6 linkages.
• Glycogen similar to amylopectin, more branches.

Cellulose and Chitin

• Cellulose: Beta 1-4 linkages, linear and dense structure.
• Chitin: Found in arthropod exoskeletons, made of N-acetylglucosamine.

Conclusion

• This section concludes with carbohydrates; the next focus will be on lipids.