Overview
This lecture covers the structure, types, and biological roles of carbohydrates, focusing on monosaccharides, disaccharides, and polysaccharides, including their digestion and physiological importance.
Carbohydrate Basics
- Carbohydrates are organic molecules made of carbon, hydrogen, and oxygen.
- The hydrogen to oxygen ratio in carbohydrates is 2:1, similar to water.
- Carbohydrates include sugars, starches, and plant fibers like cotton.
Monosaccharides
- Monosaccharides are the monomers (building blocks) of carbohydrates.
- Glucose (C6H12O6) is the main fuel for cellular respiration and the product of photosynthesis.
- In living cells, glucose usually exists in a ring form.
- Fructose is a structural isomer of glucose, found naturally in fruit, and shares the same chemical formula but has a different structure.
Disaccharides
- Disaccharides are formed by joining two monosaccharides via a covalent (glycosidic) bond.
- Maltose consists of two glucose molecules linked by an alpha 1-4 glycosidic linkage; enzymes can break this into two glucose monosaccharides.
- Sucrose (table sugar) is made of glucose and fructose joined by an alpha 1-2 glycosidic linkage and is digestible by humans.
- Lactose (milk sugar) is made of glucose and galactose with a beta 1-4 glycosidic linkage; requires lactase enzyme to digest.
Lactose Intolerance
- Most mammals lose the ability to digest lactose (milk sugar) after infancy due to reduced lactase enzyme production.
- Some adult humans can digest lactose due to a genetic mutation maintaining lactase production.
- Lactose intolerance results in digestive issues; solutions include lactose-free products and lactase supplements.
Polysaccharides
- Polysaccharides are carbohydrate polymers made of many monosaccharides.
- Starch (amylose and amylopectin) is a glucose polymer used by plants for energy storage.
- Amylose is a straight chain of glucose with alpha 1-4 linkages; amylopectin is branched, with additional alpha 1-6 linkages.
- Glycogen is the animal equivalent of starch, highly branched, and stored in liver and muscles for energy.
- Blood sugar levels are managed by converting glucose and glycogen, regulated by hormones like insulin and glucagon.
Cellulose and Digestion
- Cellulose is a glucose polymer with beta 1-4 linkages, forming plant cell walls and providing structural strength.
- Humans and most animals cannot digest cellulose due to lack of necessary enzymes.
- Some mammals and insects digest cellulose through mutualistic relationships with bacteria or protozoa.
Key Terms & Definitions
- Monosaccharide — Simple sugar molecule, basic unit of carbohydrates.
- Glucose — A six-carbon monosaccharide; main cellular energy source.
- Fructose — A structural isomer of glucose, found in fruit.
- Disaccharide — Carbohydrate made of two monosaccharides linked together.
- Glycosidic linkage — Covalent bond joining carbohydrate monomers.
- Lactase — Enzyme required to digest lactose.
- Polysaccharide — Large carbohydrate polymer made of many monosaccharides.
- Starch — Plant polysaccharide for energy storage.
- Glycogen — Animal polysaccharide for energy storage.
- Cellulose — Structural polysaccharide in plant cell walls.
Action Items / Next Steps
- Complete the interactive carbohydrate tutorial at sciencemusicvideos.com.