Overview
This lecture provides an in-depth look at carbohydrates, their structure, types, functions, digestion, health effects, and their role in nutrition and disease.
Carbohydrate Structure and Classification
- Carbohydrates are made from monosaccharides (single sugar units).
- Disaccharides consist of two monosaccharides linked together.
- Polysaccharides are chains of more than 10 monosaccharides.
- Monosaccharides include glucose (blood sugar), fructose (fruit sugar), and galactose.
Disaccharides and Bonds
- Maltose: two glucose molecules.
- Sucrose: glucose + fructose (table sugar).
- Lactose: glucose + galactose (milk sugar).
- Monosaccharides link via condensation (removing water); split by hydrolysis (adding water).
- Atoms must maintain specific bond numbers: Hydrogen (1), Oxygen (2), Nitrogen (3), Carbon (4).
Polysaccharides
- Glycogen: animal storage of glucose (in liver and muscles).
- Starch: plant storage of glucose.
- Fiber: indigestible carbohydrate, not fully broken down or absorbed by humans.
Types and Benefits of Fiber
- Soluble fiber dissolves in water, helps with diarrhea, and lowers cholesterol by trapping bile.
- Insoluble fiber does not dissolve, aids with constipation by adding bulk.
- Regular fiber intake can reduce heart disease risk by lowering blood cholesterol.
- Fiber slows digestion, manages diabetes, helps with weight management, and may reduce colon cancer risk.
- Excess fiber may cause digestive discomfort; increase intake gradually with water.
Carbohydrate Digestion and Absorption
- Begins in the mouth with salivary amylase.
- Pancreatic amylase in the small intestine breaks polysaccharides into disaccharides.
- Disaccharide-specific enzymes on microvilli (maltase, sucrase, lactase) convert disaccharides to monosaccharides for absorption.
- Lactose intolerance results from lactase deficiency.
Blood Glucose Regulation
- Insulin (lowers blood glucose by promoting glycogen storage) and glucagon (raises blood glucose by breaking down glycogen) regulate blood sugar.
- Excess glucose is converted to fat if glycogen stores are full.
- The body can make glucose from protein (gluconeogenesis) or generate ketones from fat during low-carb intake.
- Ketone buildup (ketoacidosis) is dangerous due to increased blood acidity.
Diabetes and Health Concerns
- Type 1 diabetes: genetic, insulin deficiency, requires insulin injections.
- Type 2 diabetes: common, associated with obesity and diet, caused by insulin resistance.
- Dental caries occur when sugar combines with mouth bacteria to form acid.
- Artificial sweeteners and sugar alcohols are alternatives that do not promote cavities.
Key Terms & Definitions
- Monosaccharide — single sugar molecule, basic unit of carbohydrates.
- Disaccharide — two joined monosaccharides.
- Polysaccharide — long chain of monosaccharides.
- Condensation — joining molecules by removing water.
- Hydrolysis — splitting molecules by adding water.
- Glycogen — storage form of glucose in animals.
- Starch — storage form of glucose in plants.
- Fiber — indigestible carbohydrate, aids digestion.
- Insulin — hormone that lowers blood glucose.
- Glucagon — hormone that raises blood glucose.
- Gluconeogenesis — making glucose from non-carb sources.
- Ketones — acidic compounds from fat metabolism.
- Lactose intolerance — inability to digest lactose due to lack of lactase.
- Diabetes — disease of blood glucose regulation.
Action Items / Next Steps
- Review carbohydrate digestion enzymes and their functions.
- Know the difference between soluble and insoluble fiber and their roles.
- Understand blood glucose regulation hormones and diabetes types.
- Complete assigned readings for further examples and details.