Carbohydrates Overview Quiz

Introduction to Biology - Lecture 4

• Lecture delivered by Allen Cheung on January 22, 2025
• Course: BIOL 1005 Introduction to Biology
• Lecture focused on Carbohydrates

Macronutrients

• Macromolecules categorized as Carbohydrates, Proteins, and Fats
• Key dietary components for energy and cellular function

Carbohydrates

• Sugars: Found in various foods (rice, noodles, bread, cakes, snacks)
• Body Function: Essential for cellular and bodily functions
• Brain Fuel: The brain requires glucose (110-145g per day) for proper functioning
• Daily Intake Recommendations: 225-325g per day

What are Carbohydrates?

• Classified as biomolecules alongside lipids, proteins, and nucleic acids
• Compounds of immense importance for biological processes
• Energy Source: Provide energy via oxidation
• Cell Building Blocks: Supply carbon for creating cell components
• Stored Energy: Act as stored chemical energy
• Structural Components: Part of the structures of cells and tissues

Carbohydrate Structure

• General Molecular Formula: Cn(H₂O)n (a hydrate of carbon)
• Basic Building Blocks: Monosaccharides (simple sugars) are the fundamental units
• Chain Structure: A single continuous carbon chain. Glucose structural representation can be in different forms (straight chain, ring, simplified ring).

Carbohydrate Classification

• Monosaccharides: Simplest form of carbohydrates
• Disaccharides: Two monosaccharides linked together
• Oligosaccharides: 3-10 monosaccharide units
• Polysaccharides: More than 10 monosaccharide units

Important Monosaccharides

• D-Ribose: Component of RNA (ribonucleic acid)
• D-Deoxyribose: Component of DNA (deoxyribonucleic acid)
• D-Galactose: Part of lactose, a milk sugar
• D-Glucose: Also known as dextrose or blood sugar, found in honey, fruits; crucial for energy production
• D-Fructose: Sweetest monosaccharide, found in fruits, honey, corn syrup

Physical Properties of Monosaccharides

• Sweet taste (fructose is the sweetest; 73% sweeter than sucrose)
• Solids at room temperature.
• Highly soluble in water (due to many hydroxyl groups)

Disaccharides

• Formed by linking two monosaccharides via a glycosidic bond
• Physiologically important disaccharides include sucrose, lactose, and maltose

Polysaccharides

• Composed of more than ten monosaccharides
• Types: Homopolysaccharides (one type of monosaccharide) and Heteropolysaccharides (multiple types)
• Main building block in polysaccharides is D-glucose.

Examples of Homopolysaccharides

• Starch: Storage carbohydrate in plants as granules
• Dextrin: Intermediate product in starch digestion
• Glycogen: Storage carbohydrate in animals, primarily in liver and muscle cells
• Cellulose: Main structural component in plant cell walls
• Chitin: Structural component of exoskeletons and fungal cell walls

Storage of Excess Sugars (Carbs)

• Plants store glucose as starch in their roots.
• Animals store glucose as glycogen in liver and muscle.

Starch—Composition

• Mixture of amylose and amylopectin
• Amylose: Linear glucose polymer with α(1,4) linkages
• Amylopectin: Branched glucose polymer with α(1,4) linkages and α(1,6) branch points.

Glycogen

• Storage form of glucose in animals
• Highly branched, like amylopectin, with α(1,6) branch linkages every 10 residues. Primarily stored as granules.

Cellulose

• Abundant organic molecule in nature
• Structural component of plant cell walls
• Composed of long chains of glucose monomers joined by β(1,4) linkages. This linkage is important as it cannot be digested by humans.

Summary of Carbohydrates

• Classification of carbohydrates
• Key monosaccharides and disaccharides
• Properties of different types of carbohydrates (polysaccharides)
• Storage forms of carbohydrates in plants and animals