B1.1 Lipids - Pre-IB Biology Work
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What are lipids made of?
Lipids are made of hydrocarbon chains (e.g. fatty acids) or hydrocarbon rings (e.g. steroids). They are nonpolar and hydrophobic (do not dissolve in water).
Why are lipids hydrophobic?
Because their hydrocarbon structures are nonpolar and repel water.
Examples of amphipathic lipids
• Phospholipids • Cholesterol • Glycolipids
How are dietary fats and steroid hormones transported in the body?
Dietary fats: in protein-coated droplets called lipoproteins Steroid hormones: bound to carrier proteins (e.g. albumin)
How does the hydrophobic nature of lipids affect their biological roles?
Waterproofing surfaces – e.g. waxes on leaves, oils on feathers Membrane structure – phospholipids form bilayers in water Nutrient absorption – aid in uptake of fat-soluble vitamins (A, D) Transport challenge – need special transport methods due to insolubility in blood
What are amphipathic lipids and why are they important?
Amphipathic lipids have both polar (hydrophilic) and non-polar (hydrophobic) regions. They stabilize cell membranes.
How are triglycerides and phospholipids formed?
Through condensation reactions between fatty acids and glycerol. An ester linkage forms between the –OH of glycerol and –COOH of a fatty acid. Water (H₂O) is produced as a by-product.
What is the structure and function of a triglyceride?
Structure: 3 fatty acid chains + 1 glycerol (3 ester linkages) Function: Energy storage and insulation
What is the structure and function of a phospholipid?
Structure: 2 fatty acids + 1 glycerol + 1 phosphate group Function: Main component of cell membranes, amphipathic
What are the three main classes of lipids? Give examples.
Simple Lipids Compound Lipids Derived Lipids
What are the three main types of fatty acids?
Saturated Monounsaturated Polyunsaturated
What’s the difference between cis and trans unsaturated fatty acids?
Cis: H on same side of double bond → kinked; common in nature Trans: H on opposite sides → straight; rare in nature (industrial or ruminant origin)
How does lipid storage differ in animals and plants?
Animals: Endotherms make saturated fats; ectotherms (cold climates) use cis-unsaturated oils Plants: Usually produce cis-unsaturated oils; tropical plants make more saturated fats than temperate ones
What are the advantages of triglycerides as energy storage molecules?
Store ~2x more energy than carbs Non-polar: no osmotic effect Long-term use only (broken down aerobically) Insoluble: harder to transport
What is the thermal insulation role of triglycerides?
Poor heat conductors = good insulation Found in cold-climate animals (e.g., seal blubber) Obese humans retain heat better but risk heat stress
Steroids Structure:
4 fused carbon rings; no fatty acids
Why do phospholipids form bilayers in water?
Hydrophilic heads face water Hydrophobic tails hide inside Amphipathic nature = spontaneous bilayer Bilayer is flexible and fluid, held by weak hydrophobic forces
Steroid properties
Nonpolar, lipophilic
Steroid Function:
Hormones (e.g., testosterone, oestradiol)
Steroid Transport:
Freely cross membranes; must bind to carrier proteins (like albumin) in blood
Steroid Synthesis sites:
Adrenal glands → corticosteroids Gonads → sex hormones
Fats vs oils: source
Fat: animals Oils : Plants / Cold-water fish
Fats vs oils: FA type
Fat: saturated Oils : unsaturated (cis)
Fats vs oils: chain shape
Fat: straight Oils : kinked