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

• One or more C=C double bonds
• Monounsaturated: 1 double bond (oleic acid, 18:1)
• Polyunsaturated: 2+ double bonds (linoleic acid, 18:2)
• Each double bond creates a "kink" in the chain

(b) Physical Properties:

Saturated:

• Straight chains pack tightly together
• Strong van der Waals forces between molecules
• Higher melting point → solid at room temperature
• Examples: butter, lard, coconut oil

Unsaturated:

• Kinked chains prevent tight packing
• Weaker intermolecular forces
• Lower melting point → liquid at room temperature
• Examples: olive oil, fish oil, vegetable oils

(c) Health Implications:

Saturated Fats:

• ⚠️ Raise LDL ("bad") cholesterol
• Associated with increased cardiovascular disease risk
• Recommendation: limit to <10% of daily calories

Unsaturated Fats:

• ✓ Lower LDL cholesterol, raise HDL ("good") cholesterol
• Omega-3 fatty acids (EPA, DHA): anti-inflammatory, heart-protective
• Omega-6 fatty acids (linoleic): essential, but balance with omega-3
• Recommendation: replace saturated with unsaturated fats

Trans Fats (Special Case):

• Artificially saturated (hydrogenation)
• Worst for health: raise LDL, lower HDL
• Should be avoided completely

$\boxed{\text{Unsaturated (kinked) → liquid, healthier; Saturated (straight) → solid, limit intake}}$