Overview
This lecture covers the structure, types, and functions of lipids, commonly known as fats, including their roles in the body and differences between lipid types.
Elements and Characteristics of Lipids
- Lipids are made of carbon, hydrogen, and oxygen; phospholipids also contain phosphorus.
- Lipids are hydrophobic, meaning they repel and do not dissolve in water.
- Lipids are more efficient than carbohydrates for energy storage.
- Functions include energy storage, insulation, composing cell membranes, and sending chemical signals (hormones).
Types of Lipids
- Four main groups: triglycerides, phospholipids, steroids, and waxes.
- Triglycerides consist of one glycerol and three fatty acids; main function is energy storage.
- Phospholipids have a glycerol, two fatty acids, and a phosphate group; major component of cell membranes.
- Steroids lack fatty acids and are made of four carbon rings; examples include cholesterol and various hormones.
- Waxes are used for waterproofing in plants and as protective earwax in humans.
Fatty Acids and Triglycerides
- Fatty acids have a hydrophobic hydrocarbon tail and a carboxyl (COOH) head.
- Saturated fatty acids have no carbon-carbon double bonds, are straight, and solid at room temperature (e.g., butter).
- Unsaturated fatty acids have one (mono-) or multiple (poly-) carbon-carbon double bonds, are bent, and liquid at room temperature (e.g., oils).
- Triglycerides with unsaturated fatty acids are healthier and less likely to be stored as fat.
Types of Unsaturated Fats
- Cis unsaturated fats: hydrogens on the same side of the double bond, naturally occurring, healthier.
- Trans unsaturated fats: hydrogens on opposite sides, created by hydrogenation, unhealthy and linked to processed foods.
Phospholipids and Cell Membranes
- Phospholipids have a hydrophilic (water-loving) phosphate head and two hydrophobic tails.
- Form the phospholipid bilayer in cell membranes, with heads facing water and tails inward.
Steroids and Cholesterol
- Steroids are lipids with four carbon rings, functioning mainly as hormones.
- Cholesterol is the base molecule for all steroids and is found in cell membranes.
- Lipoproteins transport cholesterol: LDL ("bad") increases artery blockage risk, HDL ("good") helps remove cholesterol from blood vessels.
Waxes
- Waxes are lipids with long fatty acid chains; provide waterproofing in plants and protective functions in animals.
Key Terms & Definitions
- Lipid — hydrophobic macromolecule made of C, H, O; includes fats, oils, and some hormones.
- Fatty Acid — hydrocarbon chain with a carboxyl group, monomer-like part of many lipids.
- Triglyceride — lipid with three fatty acids and a glycerol, main storage form of fat.
- Phospholipid — lipid with two fatty acids, a glycerol, and a phosphate group; forms cell membranes.
- Steroid — lipid with four fused carbon rings, functions as hormones.
- Saturated Fat — fatty acid with no double bonds; solid at room temperature.
- Unsaturated Fat — fatty acid with one or more double bonds; liquid at room temperature.
- Cis Fat — unsaturated fat with hydrogens on the same side of the double bond.
- Trans Fat — unsaturated fat with hydrogens on opposite sides; unhealthy.
- Lipoprotein — molecule that transports cholesterol and fats in the blood.
- LDL/HDL — low/high density lipoproteins; "bad" and "good" cholesterol carriers, respectively.
Action Items / Next Steps
- Review the diagrams and structures of triglycerides, phospholipids, and steroids.
- Prepare questions on lipid functions and health impacts for class discussion.
- Be ready to analyze food labels for trans fats and discuss hydrogenation in class.