Overview
This lecture covers the structure, types, properties, and health implications of lipids, focusing on fatty acids, membrane lipids, steroids, and their roles in biology and nutrition.
Classification and Properties of Lipids
- Lipids are hydrophobic biomolecules insoluble in water and do not form polymers.
- Two main lipid classes: those derived from fatty acids and from isoprenoids.
- Fatty-acid-derived lipids include triacylglycerols (energy storage), waxes (waterproofing), phospholipids, and sphingolipids (membrane structure).
- Isoprenoid-derived lipids include steroids, lipid-soluble vitamins, and terpenes.
Fatty Acids: Structure and Nomenclature
- Fatty acids have a carboxylic acid group and a long hydrocarbon tail.
- IUPAC naming: carboxyl carbon is C1; omega notation names the last carbon as omega.
- Saturated fatty acids have no double bonds; unsaturated have one (monounsaturated) or multiple (polyunsaturated) cis double bonds.
- Melting point increases with chain length and decreases with more double bonds.
Key Fatty Acids and Their Health Roles
- Essential fatty acids, like linoleic (omega-6) and alpha-linolenic (omega-3), must be obtained from the diet.
- Omega-3 fatty acids (EPA, DHA) are found in fish oil and are beneficial for health.
- Fatty acids are stored as triacylglycerols in adipocytes (fat cells) for energy and insulation.
- Unsaturated fats (from plants) are generally liquid at room temperature and healthier than saturated fats (from animals).
Lipids in Foods and Health Implications
- Plant oils are rich in unsaturated fatty acids; animal fats have more saturated fatty acids.
- Saturated and trans fats increase risk of cardiovascular disease; unsaturated fats reduce it.
- Cholesterol is found only in animal fats and can negatively affect cardiovascular health if excessive.
- Trans fatty acids are produced by hydrogenation and increase health risks.
Membrane Lipids
- Glycerol phospholipids and sphingolipids are key membrane components, forming bilayers with hydrophilic heads and hydrophobic tails.
- Sphingolipids (ceramide, cerebroside, ganglioside) are abundant in nervous tissue.
Steroids and Isoprenoids
- Steroids (e.g., cholesterol, hormones) have a four-ring structure and are hydrophobic.
- Cholesterol is crucial for membrane fluidity and hormone/vitamin D synthesis but excess leads to artery plaque.
- Lipoproteins (LDL = "bad", HDL = "good") transport cholesterol and triacylglycerols in blood.
Key Terms & Definitions
- Fatty Acid โ Carboxylic acid with a long hydrocarbon chain.
- Triacylglycerol โ Glycerol molecule esterified with three fatty acids; main fat storage.
- Phospholipid โ Membrane lipid with glycerol, two fatty acids, and a phosphate polar head group.
- Sphingolipid โ Membrane lipid based on sphingosine, common in nerve cells.
- Cholesterol โ Steroid lipid found in animal cells, precursor of hormones and vitamin D.
- Lipoprotein โ Complex of lipids and proteins for lipid transport in blood.
- Saturated/Unsaturated Fat โ Fatty acids without/with double bonds.
- Trans Fatty Acid โ Fatty acids with trans double bonds, linked to health risks.
- Essential Fatty Acid โ Fatty acids that must be obtained through diet.
Action Items / Next Steps
- Find shorthand notations for EPA and DHA and research their health benefits.
- Look up polyunsaturated fatty acids in infant formula and their health roles.
- Review the lipid profile section of blood test reports.