Biological Macromolecules 2 - Carbs & Lipids

Overview of Biological Macromolecules

• Recap of previous video: Types of biological macromolecules and their formation/breakdown.

• Focus of this video: Carbohydrates and lipids.

Carbohydrates

Definition and Structure

• Carbohydrates are made up of sugar molecules; they are polymers consisting of monomers (monosaccharides).

• Common thought of carbohydrates as food-related items (e.g., pasta, candy).

Types of Carbohydrates

Simple Sugars (Monosaccharides)

• Composed of 1 to about 8 monosaccharides.

• Sweet in taste, typically end in "-ose" (e.g., glucose, fructose).

Complex Carbohydrates (Polysaccharides)

• Formed by multiple monosaccharides.

• Common sources include grains and vegetables; stored in plants as starch.

• Fiber: Non-digestible carbohydrate critical for digestion; includes soluble (helps with fullness, reduces cholesterol) and insoluble (adds bulk to feces).

Monosaccharide Structure

• Typically contain 5-6 carbons (e.g. ribose has 5 carbons).

• General formula: Cn(H2O)n (indicative of hydrated carbon).

• Hydrogen is usually twice as abundant as carbon and oxygen.

Formation of Carbohydrates

• Joining monosaccharides yields disaccharides (e.g., sucrose, lactose) through dehydration reactions, forming glycosidic linkages.

• Polysaccharides include starch, glycogen (energy storage in humans), cellulose (plant structure), and chitin (arthropod exoskeleton, indigestible).

Lipids

Definition and Structure

• Lipids are macromolecules not categorized as polymers, predominantly composed of carbon and hydrogen, forming non-polar, hydrophobic molecules.

• Four main types: Triglycerides, phospholipids, steroids, and waxes.

Types of Lipids

Triglycerides

• Common dietary fat, consists of a glycerol molecule and three fatty acid tails.

• Acts as energy storage; categorized as saturated, unsaturated, or trans fats based on carbon bond types.

Phospholipids

• Composed of glycerol, two fatty acid tails, and a phosphate group (making it amphipathic).

• Essential for cell membranes—form lipid bilayers.

Steroids

• Characterized by four fused carbon rings; act as signaling molecules (examples: testosterone, estrogen).

• Cholesterol is crucial for membrane fluidity and lipid transport.

Waxes

• Provide protective barriers in nature, commonly found on plant surfaces to prevent water loss; also seen in bacteria like Mycobacterium tuberculosis for immune evasion.

Fatty Acid Classification

Saturated Fats

• Only single bonds between carbons, typically solid at room temperature.

Unsaturated Fats

• Contain one or more double bonds, causing bends in the structure, usually liquid at room temperature.

• Double bonds influence fat behavior and shape (cis vs. trans forms).

• Trans Fats: Synthetic modification turning unsaturated fats into shapes resembling saturated fats—considered unhealthy.

Recap Questions

1. Monomer of Carbohydrate: Monosaccharide.

2. Bond between Monomers: Glycosidic linkage.

3. Molecular Formula for Carbohydrates: Cn(H2O)n.

4. Properties of Lipids: Non-polar, hydrophobic.

5. Amphipathic Definition: Molecules that are both hydrophilic (water-attracting) and hydrophobic (water-repelling).

6. Identification of Fatty Acids: Unsaturated if double bonds present (causing bends).

Looking Ahead

• Next video will cover proteins and nucleic acids as further macromolecules.