Overview
This lecture covers the main types of lipids, including fatty acids, triglycerides, phospholipids, and cholesterol, focusing on their structures, properties, and functions.
Fatty Acids
- Fatty acids are lipids with long hydrocarbon tails and a carboxyl group at one end.
- The carbon-to-hydrogen ratio is close to 1:2 in fatty acids.
- Saturated fatty acids have only single bonds between carbons and are full of hydrogen atoms.
- Unsaturated fatty acids have at least one double bond between carbon atoms, causing a kink in the molecule.
- Monounsaturated fatty acids have one double bond; polyunsaturated have more than one.
- Hydrocarbon tails are nonpolar and do not mix with water, while the head (carboxyl group) is polar.
- The carboxyl group can release a proton, making fatty acids acidic.
Triglycerides
- Triglycerides are made of one glycerol molecule bonded to three fatty acids.
- Glycerol is a three-carbon sugar alcohol with hydroxyl groups.
- Each fatty acid attaches to glycerol, releasing water in the process (dehydration synthesis).
- Mono-, di-, and triglycerides have one, two, or three fatty acids attached to glycerol, respectively.
- There is no room for more than three fatty acids on one glycerol.
Phospholipids
- Phospholipids have a glycerol backbone, two fatty acid tails, and one phosphate group.
- The phosphate group is polar, making the “head” of the molecule hydrophilic (water-loving).
- The fatty acid tails are nonpolar and hydrophobic (water-fearing).
- Phospholipids are key structural components of cell membranes.
- Glycolipids- a sugar(monosaccharide) added to the head of the phospholipid instead of a phosphate group.
Cholesterol and Steroids
- Cholesterol is based on a four-ring carbon structure.
- It is a key component in cell membranes, providing stiffness.
- Cholesterol is the precursor for steroid hormones like cortisol, estrogen, progesterone, and testosterone.
- The liver can synthesize cholesterol; excess cholesterol can lead to health risks such as coronary artery disease.
Key Terms & Definitions
- Fatty Acid — A lipid with a long hydrocarbon tail and a carboxyl group.
- Saturated Fatty Acid — Fatty acid with only single bonds between carbons.
- Unsaturated Fatty Acid — Fatty acid with one or more double bonds between carbons.
- Triglyceride — A lipid composed of glycerol and three fatty acids.
- Glycerol — A three-carbon molecule with hydroxyl groups; backbone of triglycerides and phospholipids.
- Phospholipid — Lipid with a glycerol backbone, two fatty acids, and a phosphate group.
- Cholesterol — A four-ring lipid essential for membranes and steroid hormone synthesis.
- Hydrophobic — Repels water; nonpolar.
- Hydrophilic — Attracts water; polar.
Action Items / Next Steps
- Review the structure and properties of fatty acids, triglycerides, phospholipids, and cholesterol.
- Prepare for discussion on the role of phospholipids in cell membrane structure in the next chapter.