Overview
This lecture covers the structure, types, and functions of lipids, including their role in cell membranes, energy storage, essential nutrients, and hormones.
Lipid Structure and Properties
- Lipids are macromolecules that do not have monomers or polymers.
- All lipids are non-polar (hydrophobic) and mostly consist of hydrocarbon chains.
- Lipids differ from carbohydrates in that they lack carbonyl or multiple hydroxyl groups.
- The basic structure includes a hydrocarbon chain and a carboxy (carboxyl) group.
Types of Fatty Acids
- Saturated fatty acids have only single bonds between carbons, are linear, and are typically solid at room temperature (animal fats).
- Unsaturated fatty acids have at least one double bond causing a bend (kink), are usually liquid at room temperature (oils).
- Saturated fats are "saturated" with hydrogen; unsaturated fats are not.
- Naturally occurring unsaturated fats are usually in the cis configuration.
Fatty Acids in the Body
- Fatty acids are mainly stored and transported as triglycerides (three fatty acids plus a glycerol).
- Essential fatty acids (omega-3 and omega-6) must come from diet; omega-9 is non-essential.
- Fatty acids support growth, brain/nervous system function, insulation, organ protection, hormone production, and absorption of fat-soluble vitamins (A, D, E, K).
- Fat cells release leptin, a hormone involved in appetite, metabolism, and other functions.
Trans Fats
- Trans fats are artificially created by hydrogenating unsaturated fats; they have a trans configuration, are linear and solid at room temperature.
- Trans fats increase bad cholesterol, lower good cholesterol, and raise the risk of heart disease, stroke, and diabetes.
- Avoid products with "partially hydrogenated" or "hydrogenated" oils.
Phospholipids and Cell Membranes
- Phospholipids consist of a hydrophilic (polar) head and two hydrophobic (non-polar) fatty acid tails (one saturated, one unsaturated).
- Both saturated and unsaturated fatty acids are used to make cell membranes.
- Membrane fluidity and selective permeability depend on the ratio of saturated to unsaturated fatty acids.
Cholesterol and Steroid Hormones
- Cholesterol is a lipid/steroid made of four fused carbon rings.
- Cholesterol stabilizes cell membranes and is a precursor for steroid hormones.
- Steroid hormones include estrogen, testosterone, and cortisol (stress hormone).
Functions and Effects of Hormones
- Hormones are chemical messengers produced in one part of the body that affect other areas.
- Lipid-based hormones (e.g., steroid hormones) are made from cholesterol; protein-based hormones (e.g., insulin) are made from proteins.
- Excess cortisol (from stress) can have damaging effects on the body.
Waxes
- Waxes are lipids important for preventing desiccation (drying out) in plants and some animals.
- In humans, wax is mainly found as earwax, protecting the ear canal.
Key Terms & Definitions
- Lipid — Non-polar macromolecule, insoluble in water, includes fats, oils, phospholipids, sterols, and waxes.
- Fatty acid — Hydrocarbon chain with a carboxyl group; building block of many lipids.
- Saturated fatty acid — Fatty acid with only single carbon bonds; solid at room temperature.
- Unsaturated fatty acid — Fatty acid with one or more double bonds; liquid at room temperature.
- Triglyceride — Three fatty acids + glycerol; main form of fat storage and transport.
- Phospholipid — Lipid with two fatty acid tails and a phosphate group; major component of cell membranes.
- Cholesterol — Steroid lipid involved in membrane stability and hormone synthesis.
- Leptin — Hormone from fat cells; regulates appetite and metabolism.
- Trans fat — Artificially hydrogenated fat with trans configuration; linked to diseases.
Action Items / Next Steps
- Review the slide set on trans fats.
- Check nutrition labels for hydrogenated oils in packaged foods.
- Ensure dietary intake of essential fatty acids (omega-3 and omega-6).
- Prepare for next class on another macromolecule.