Overview
This lecture covers the main types of lipids, their structures, functions, and significance in biological systems, with a focus on their nonpolar, hydrophobic nature.
Lipid Basics
- Lipids are nonpolar hydrocarbon molecules, making them hydrophobic (do not mix with water).
- Common lipid types include triglycerides, phospholipids, prostaglandins, and steroids.
Triglycerides
- Triglycerides consist of one glycerol molecule and three fatty acid chains.
- Fatty acids can be saturated (no double bonds; straight chains) or unsaturated (contain double bonds; bent chains).
- Saturated fats (e.g., butter) are solid at room temperature; unsaturated fats (e.g., olive oil) are liquid.
- Triglycerides store large amounts of energy in their fatty acid chains.
- Hydrolysis of triglycerides releases energy and produces ketone bodies in the liver.
- Excess ketone bodies can lower blood pH, leading to ketoacidosis, especially during no-carb diets.
- Early signs of ketosis include fruity-smelling breath.
Phospholipids
- Phospholipids have a glycerol backbone, two fatty acid chains, and a phosphate group.
- The phosphate group creates a polar head, allowing interaction with water.
- Phospholipids are the main component of cell membranes, forming bilayers in aqueous environments.
Prostaglandins
- Prostaglandins are lipid-derived messenger molecules used in local cell-to-cell communication.
- They regulate blood vessel diameter and are involved in processes like blood clotting.
Steroids
- Steroids are distinguished by four carbon rings (three six-carbon and one five-carbon ring).
- Steroids are nonpolar and include cholesterol as a main example.
- Cholesterol is a precursor for steroid hormones (testosterone, estrogen) and vitamin D.
- Cholesterol is crucial for animal cell membrane structure and fluidity.
Key Terms & Definitions
- Lipid — Hydrophobic, nonpolar biological molecule mainly composed of hydrocarbons.
- Triglyceride — Lipid with one glycerol and three fatty acids; main energy storage molecule.
- Saturated fatty acid — Fatty acid without double bonds, fully "saturated" with hydrogen.
- Unsaturated fatty acid — Fatty acid with one or more double bonds, not fully saturated.
- Ketone bodies — Molecules produced from fatty acid breakdown; can affect blood pH.
- Phospholipid — Lipid with two fatty acids and a phosphate group; main component of cell membranes.
- Prostaglandin — Lipid molecule involved in short-range cell signaling.
- Steroid — Lipid with four fused carbon rings; includes cholesterol and hormone precursors.
- Cholesterol — Steroid involved in membrane structure and as a precursor for hormones and vitamins.
Action Items / Next Steps
- Review the characteristics and roles of each lipid type.
- Monitor for early signs of ketosis if considering a no-carb diet.
- Prepare for upcoming chapters on metabolism and ketone bodies.