🧈 Lipids

Overview

Lipids: Hydrophobic (nonpolar) biological molecules

• Not true polymers (no repeating monomers)
• Mostly composed of C, H, with some O
• Functions: energy storage, membranes, signaling, insulation

Types of Lipids

1. Fats and Oils (Triglycerides)

Structure:

• 1 glycerol + 3 fatty acids
• Linked by ester bonds (dehydration synthesis)

Fatty Acids:

• Long hydrocarbon chains (C-C-C...)
• Carboxyl group (-COOH) at one end

Saturated vs. Unsaturated:

| Saturated | Unsaturated | |-----------|-------------| | No C=C double bonds | One or more C=C double bonds | | Straight chains | Kinks at double bonds | | Pack tightly | Pack loosely | | Solid at room temp (fats) | Liquid at room temp (oils) | | Animal sources | Plant sources | | Higher melting point | Lower melting point |

Energy Storage:

• More than 2× energy per gram vs. carbohydrates
• Efficient long-term storage
• Adipose tissue in animals

2. Phospholipids

Structure:

• Glycerol + 2 fatty acids + phosphate group
• Amphipathic: hydrophilic head + hydrophobic tails

Biological Role:

• Cell membrane structure
• Form bilayers in aqueous solution
• Heads face water, tails face each other
• Selectively permeable barrier

3. Steroids

Structure:

• Four fused carbon rings
• Different functional groups attached

Examples:

• Cholesterol: membrane fluidity, precursor to other steroids
• Sex hormones: testosterone, estrogen
• Cortisol: stress hormone

Key Concepts

1. Lipids are hydrophobic (don't dissolve in water)
2. Triglycerides store energy efficiently
3. Saturated fats have no double bonds, pack tightly (solid)
4. Unsaturated fats have double bonds, don't pack well (liquid)
5. Phospholipids form cell membranes (bilayer structure)
6. Steroids have ring structure, various functions