Biology Chapter 4 - Carbohydrates

Carbohydrates Overview

• Carbohydrates are essential energy sources for all cells, composed of carbon, hydrogen, and oxygen.
• Rich dietary sources include fruits, vegetables, and grains.

Types of Carbohydrates

• Glucose: The most abundant carbohydrate, produced by plants via photosynthesis.
• Simple Carbohydrates: Comprise one or two sugar molecules, commonly known as sugars.
• Monosaccharides: Single-molecule carbohydrates like glucose, fructose, and galactose.
• Disaccharides: Formed from two monosaccharides, examples include lactose, maltose, and sucrose.
• Oligosaccharides: Contain 3 to 10 monosaccharides.
• Polysaccharides: Composed of hundreds to thousands of glucose molecules; include starch, glycogen, and fiber.

Specific Carbohydrates

• Starch: A complex carbohydrate, primarily stored in plants. Exists as:
  • Amylose: Straight-chain glucose.
  • Amylopectin: Branched-chain glucose.
  • Resistant Starch: Indigestible fiber linked by beta bonds, found in grains, legumes, fruits, and vegetables.
• Glycogen: Animal storage form of glucose, found in liver and muscles, but not in the diet.
• Fiber: Long polysaccharide chains with two types:
  • Dietary Fiber: Non-digestible parts of plants.
  • Functional Fiber: Extracted carbohydrates with known health benefits.

Fiber Types

• Soluble Fiber: Dissolves in water; contributes to fullness, heart health, and glycemic control. Found in citrus, berries, oats, and beans.
• Insoluble Fiber: Does not dissolve in water; promotes digestive health and regularity. Found in whole grains, seeds, and vegetables.

Digestion

• Carbohydrate digestion occurs in the small intestine, not the stomach.
• Enzymes like maltase, sucrase, and lactase convert disaccharides to monosaccharides, which are absorbed into the bloodstream.
• The liver converts all absorbed monosaccharides to glucose.

Blood Glucose Regulation

• Regulated by hormones: insulin, glucagon, epinephrine, norepinephrine, cortisol, and growth hormone.
  • Insulin: Promotes glucose uptake and glycogen storage.
  • Glucagon: Stimulates glucose release from glycogen.
  • Epinephrine/Norepinephrine: Increase blood glucose during stress ("fight or flight").
  • Cortisol/Growth Hormone: Influence glucose production and utilization.

Glycemic Index (GI)

• Measures a food's potential to raise blood glucose.
  • High GI: Causes sudden blood glucose spikes.
  • Low GI: Ensures stable glucose levels; benefits include reduced risks for heart disease and colon cancer.
• Glycemic Load: Assesses the overall impact of foods on blood glucose, calculated from carbohydrate content multiplied by its GI.

Energy and Ketosis

• Red blood cells rely solely on glucose for energy.
• Carbohydrates and fats supply energy; glucose is crucial during exercise.
• In fasting states, fats produce ketones, which can lead to ketoacidosis if excessive.

Recommended Carbohydrate Intake

• RDA: 130 grams/day for adequate brain glucose.
• AMDR: 45% to 65% of daily caloric intake.

Fiber and Sweeteners

• Adequate Fiber Intake: 25 g/day for women, 38 g/day for men.
• Nutritive Sweeteners: Include sugars like sucrose and provide 4 kcal/g.
• Non-Nutritive Sweeteners: Provide little to no energy, safe for various populations.

Diabetes

• Refers to inability to regulate blood glucose levels:
  • Type 1 Diabetes: Autoimmune, results in little insulin production.
  • Type 2 Diabetes: Characterized by insulin resistance; linked to obesity and lifestyle factors.

Hypoglycemia

• Reactive Hypoglycemia: Excessive insulin release post-high carbohydrate meals.
• Fasting Hypoglycemia: Overproduction of insulin despite fasting.

Conclusion

• Understanding carbohydrates, their types, digestion, regulation, and health implications is vital for proper nutrition and management of conditions like diabetes.

Test your knowledge of carbohydrates with this quiz based on Chapter 4. Explore the definition, types, and functions of carbohydrates as important energy sources. Perfect for biology students looking to solidify their understanding of plant-derived energy nutrients.