AP Biology AP Biology 1.5 Lipids Study Notes- New Syllabus Effective 2025
AP Biology 1.5 Lipids Study Notes- New syllabus
AP Biology 1.5 Lipids Study Notes – AP Biology – per latest AP Biology Syllabus.
LEARNING OBJECTIVE
Describe the structure and function of lipids.
Key Concepts:
- Triglycerides
- Phospholipids
- Steroids
1.5.A – Lipids: Structure & Function
🧱 What are lipids made of?
- Not true polymers (no repeating monomers like in carbs or proteins)
- Mostly made of carbon (C), hydrogen (H), and oxygen (O)
- Lipids are hydrophobic (don’t mix with water) due to nonpolar bonds
🧪 Major Types of Lipids:
| Type | Structure | Function |
|---|---|---|
| Fats (Triglycerides) | Glycerol + 3 fatty acids | Long-term energy storage, insulation |
| Phospholipids | Glycerol + 2 fatty acids + phosphate group | Make up cell membranes |
| Steroids | 4 fused carbon rings (no fatty acids) | Hormones (like testosterone, estrogen), cholesterol in membranes |
| Waxes | Long chains of alcohol + fatty acids | Waterproofing in plants and animals |
🔍 Types of Fatty Acids:
- Saturated fats:
- No double bonds (straight chain)
- Solid at room temp (e.g. butter)
- Unsaturated fats:
- Have one or more double bonds (kinked chain)
- Liquid at room temp (e.g. olive oil)
🧬 Functions of Lipids:
- Energy storage – 1 gram of fat stores more energy than 1g of carbs or proteins
- Insulation & protection – Fat cushions organs and keeps us warm
- Cell structure – Phospholipids form the bilayer of cell membranes
- Signaling – Steroids act as hormones that regulate body processes
🧠Note:
Lipids are NOT polymers, but they’re still macromolecules.
1.5.A.1 – Structure & Function of Lipids
🧪 What are Lipids?
- Large, nonpolar, and hydrophobic molecules
- Insoluble in water (a polar solvent)
- Soluble in nonpolar solvents (e.g., ether, chloroform)
- Not true polymers, but built from subunits like fatty acids and glycerol
💧 Fatty Acids: The Building Blocks
Saturated Fatty Acids:
- Only single bonds between carbon atoms (C–C)
- Each carbon is “saturated” with hydrogen
- Straight chain → pack tightly → solid at room temp
- Found in: butter, animal fats, coconut oil
Unsaturated Fatty Acids:
- Contain at least one double bond (C=C)
- Double bonds create “kinks,” preventing tight packing
- Result: liquid at room temperature
- Monounsaturated (MUFA): 1 double bond (e.g., olive oil)
- Polyunsaturated (PUFA): 2+ double bonds (e.g., omega-3, omega-6)
- Essential fatty acids: Must come from the diet
- Linoleic acid (omega-6)
- Alpha-linolenic acid (omega-3)
🧠 Cis vs. Trans Configuration
- Cis: H atoms on the same side → natural & healthy
- Trans: H atoms on opposite sides → from hydrogenation → health risks
🫀 Health & Function
- MUFA & PUFA: Heart-friendly fats
- Help lower LDL (bad cholesterol)
- Improve blood vessel function
- Reduce inflammation
- Omega-3: Important for brain health, immunity, and reducing heart disease risk
🍳 Sources of Good Fats
| Type | Rich Sources |
|---|---|
| MUFA | Olive oil, nuts, avocados |
| PUFA | Fatty fish, flaxseeds, walnuts, soybean oil |
🧴 Food & Chemistry Notes
- Oils (rich in unsaturated fats) = Liquid at room temperature
- Double bonds make unsaturated fats prone to oxidation → rancidity
- Antioxidants (e.g., Vitamin E) help prevent this by protecting fats
📝 Summary:
- Saturated = No double bonds → solid
- Unsaturated = One or more double bonds → liquid
- Healthy lipids = More unsaturated fats in diet
1.5.A.2 — Functions of Lipids in Living Organisms
Lipids are more than just fat — they serve several vital roles in the body. Let’s break it down:
🧃 1. Fats (Triglycerides)
- Made of glycerol + 3 fatty acids
- Primary function: Long-term energy storage
- Also help with:
- Cushioning and protecting organs
- Thermal insulation (e.g., blubber in whales)
🧬 2. Steroids
- Lipids with a 4-ring structure
- Includes hormones like:
- Estrogen & Testosterone: Growth, development, reproduction
- Cortisol: Regulates stress, metabolism, immune response
- Function: Support homeostasis and metabolic functions
🧱 3. Cholesterol
- A type of steroid found in animal cell membranes
- Maintains: Membrane fluidity and stability across temperatures
- Also: Precursor for other steroids (hormones, vitamin D)
🧫 4. Phospholipids
- Structure: Glycerol + 2 fatty acids + phosphate group
- Have a hydrophilic (water-loving) head and hydrophobic (water-fearing) tails
- Function: Form lipid bilayers in:
- Plasma membranes
- Organelle membranes
- Role: Regulates what enters and exits the cell
📝 Recap Table:
| Lipid Type | Function |
|---|---|
| Fats | Energy storage, insulation, cell function |
| Steroids | Hormones for growth, metabolism, homeostasis |
| Cholesterol | Stabilizes animal membranes |
| Phospholipids | Form cell membrane bilayers |