Overview
This lecture covers the structure, types, and functions of carbohydrates, focusing on their chemical makeup, biological roles, and digestion processes.
Carbohydrate Structure & Composition
- Carbohydrates are made of carbon, hydrogen, and oxygen atoms.
- Their structure is often a ring shape.
- They are one of four main macromolecule types: carbohydrates, proteins, fats, and nucleic acids.
Types of Carbohydrates
- Carbohydrates exist as monosaccharides (one sugar), disaccharides (two sugars linked), or polysaccharides (many sugars linked).
- Monosaccharides include glucose, fructose, and galactose, all with formula C6H12O6.
- These sugars are isomers—same formula, different atomic arrangements.
Biological Role of Carbohydrates
- Carbohydrates provide primary energy for the body.
- They are found on cell membranes and associated with genetic material.
- Only about 1% of human body mass is carbohydrate.
Disaccharides: Formation and Digestion
- Disaccharides form via dehydration reactions (removing water); examples: sucrose (glucose + fructose), lactose (glucose + galactose).
- Breaking disaccharides apart requires rehydration (adding water) and specific enzymes.
- Lactase enzyme splits lactose; absence causes lactose intolerance and related digestive issues like diarrhea due to osmotic effects.
Polysaccharides: Storage and Dietary Sources
- Polysaccharides are chains of glucose molecules; types include starch, cellulose (plants), and glycogen (animals).
- Humans store glucose as glycogen.
- Cellulose is dietary fiber in humans; we lack enzymes to digest it, so it aids stool bulk.
- Starch and glycogen are digestible; cellulose is not.
Key Terms & Definitions
- Monosaccharide — single sugar molecule (e.g., glucose, fructose, galactose)
- Disaccharide — two monosaccharides linked together
- Polysaccharide — complex chain of many monosaccharides
- Dehydration reaction — a chemical process that links molecules by removing water
- Rehydration (Hydrolysis) — process that splits molecules by adding water
- Lactase — enzyme that breaks down lactose
- Osmotic effect — movement of water in intestines due to undigested molecules
Action Items / Next Steps
- Review diagrams of carbohydrate structures (monosaccharide, disaccharide, polysaccharide).
- Read about enzyme digestion and absorption of carbohydrates.