There are three major groups of lipids: triglycerides, phospholipids, and steroids. Triglycerides are made of glycerol linked to three fatty acid chains that can be saturated, monounsaturated, or polyunsaturated depending on the number of double bonds in the fatty acid chains. Phospholipids have one fatty acid replaced by a phosphate group, giving them both hydrophobic and hydrophilic ends. Steroids have a backbone of four interconnected carbon rings, and important examples include cholesterol, a component of cell membranes, and the sex hormones estradiol and testosterone.

1. Lipids 1. Fats 2. Phospholipids 3. steroids -nonpolar (hydrophobic)‏ -insoluble (can’t dissolve) in water and other polar substances

3. 3 Major Groups: Triglycerides (fats) – glycerol molecule linked to 3 fatty acid chains Note that the fatty acid chains are made up of long chains of hydrocarbons with a carboxyl group at one end

4. Triglycerides can be saturated, monounsaturated, or polyunsaturated Saturated – maximum# of H added to C backbone - solid at room temperature

5. Monounsaturated – one double bonded carbon in chain - liquid at room temperature

6. Polyunsaturated – two or more double bonded carbons in chain -liquid at room temperature

7. 2. Phospholipids -one fatty acid chain is replaced by a phosphate group (+R)‏ -hydrophobic end and hydrophilic end

8. 3. Steriods -backbone of 4 interconnected carbon rings (3 hexose, 1 pentose)‏

9. Biologically Important Steroids Cholesterol – component of cell membrane (controls fluidity)‏ - starting ingredient for synthesis steroid hormones Difference between Good (HDL) and Bad (LDL) Cholesterol

10. Estradiol – female sex hormone

11. Testosterone – male hormone