Overview
This lecture covers lipids—types, structures, properties, health implications, and biological functions—focusing on fats, phospholipids, and steroids.
Introduction to Lipids
- Lipids are hydrophobic biomolecules made mostly of nonpolar hydrocarbons.
- Lipids do not form true polymers.
- Major types: fats, phospholipids, and steroids.
Fats (Triglycerides)
- Fats are also called triglycerides, formed from one glycerol and three fatty acids.
- Glycerol is a three-carbon alcohol; fatty acids are hydrocarbon chains with a carboxyl group.
- Formation involves dehydration reactions, creating ester linkages and releasing water.
- Fatty acids vary by chain length and double bond presence/location.
Saturated vs Unsaturated Fats
- Saturated fatty acids have no double bonds; they are solid at room temperature (e.g., butter, animal fat).
- Unsaturated fatty acids have one or more double bonds; they are usually liquid at room temperature (e.g., vegetable oils, fish fats).
- Double bond configuration leads to cis and trans isomers with different properties.
Trans Fats and Health
- Trans fats are formed by partial hydrogenation of unsaturated fats, converting cis to trans isomers.
- Trans fats increase cardiovascular disease risk more than saturated fats.
- Many foods now avoid trans fats due to health concerns.
Good Fats: Omega Fatty Acids
- Omega-3 and omega-6 fatty acids are essential fats with double bonds near the omega (tail) end.
- Omega-3s are linked to reduced cardiovascular disease risk and must be obtained from diet.
- Avocados contain monounsaturated fatty acids (MUFAs), considered beneficial.
Biological Functions of Fats
- Fats provide long-term energy storage, insulation, and organ protection in animals.
- Adipose (fatty) tissue stores energy and cushions organs.
- Plants store fats in seeds for energy for seedling growth.
Phospholipids
- Phospholipids consist of glycerol, two fatty acids, and a phosphate group.
- Fatty acid tails are hydrophobic; phosphate head is hydrophilic, making the molecule amphipathic.
- Phospholipids form bilayers, which make up cell membranes.
Steroids
- Steroids have a core structure of four fused carbon rings.
- Examples: cholesterol, estradiol, and testosterone.
- Steroids function as hormones and are mostly hydrophobic.
- Cholesterol is essential but excess can harm cardiovascular health.
Key Terms & Definitions
- Lipid — Hydrophobic biomolecule made mostly of hydrocarbons.
- Fat (Triglyceride) — Molecule of glycerol linked to three fatty acids.
- Fatty Acid — Hydrocarbon chain with a carboxyl group.
- Saturated Fat — Fatty acid with no double bonds, solid at room temperature.
- Unsaturated Fat — Fatty acid with one or more double bonds, usually liquid at room temperature.
- Trans Fat — Artificial fat created by hydrogenation, with trans double bonds.
- Omega-3 Fatty Acid — Essential fat with a double bond three carbons from the omega end.
- Phospholipid — Lipid with glycerol, two fatty acids, and a phosphate group.
- Amphipathic — Molecule with both hydrophilic and hydrophobic parts.
- Steroid — Lipid with four fused carbon rings, often a hormone.
Action Items / Next Steps
- Review chapter 5 up to proteins.
- Prepare for the next lecture on proteins.