Overview
This lecture introduces disaccharides, focusing on their structure, formation, examples (sucrose and lactose), and the role of enzymes in their digestion.
Disaccharides: Structure and Formation
- Disaccharides are carbohydrates made of two monosaccharides bonded together.
- Common disaccharides include sucrose (table sugar) and lactose (milk sugar).
- The bond joining two monosaccharides is called a glycosidic linkage.
- Disaccharides form by a condensation reaction, releasing a water molecule.
- Breaking apart disaccharides into monosaccharides is called hydrolysis, which uses up a water molecule.
Sucrose
- Sucrose is a disaccharide formed from glucose and fructose.
- Found naturally in plants; common source is table sugar.
- Sucrose is mainly extracted from sugar cane and sugar beet plants.
- Diagrammatically, sucrose consists of a six-membered ring (glucose) and a five-membered ring (fructose) joined together.
Lactose
- Lactose is a disaccharide composed of glucose and galactose.
- It is found in dairy products and makes up 2-8% of milk.
- Many cheeses and yogurts have less lactose because bacteria consume it during processing.
- Lactose consists of two six-membered rings (glucose and galactose) joined together.
Enzymes and Lactose Intolerance
- Enzymes are proteins that help break down disaccharides into monosaccharides.
- Lactase is the enzyme that breaks down lactose; sucrase breaks down sucrose.
- Lactose intolerance occurs when the body lacks lactase, making digesting lactose difficult.
Key Terms & Definitions
- Disaccharide — a carbohydrate made from two monosaccharides bonded together.
- Monosaccharide — the simplest form of carbohydrate (e.g., glucose, fructose, galactose).
- Glycosidic linkage — the bond that joins two monosaccharides in a disaccharide.
- Condensation reaction — a chemical reaction that joins two molecules and releases water.
- Hydrolysis — a reaction that breaks a bond using water.
- Enzyme — a protein that speeds up chemical reactions in the body.
- Lactase — an enzyme that breaks down lactose.
- Lactose intolerance — inability to digest lactose due to lack of lactase.
Action Items / Next Steps
- Research and answer the 10 questions about lactose intolerance in your notes.
- Show your completed work to the teacher for review.