1. Lipids
Section 3.3

2. Learning Objectives
Relate the structure of lipids to their function in living systems
Distinguish among fats, phospholipids, & steroids
Explain the difference between saturated and unsaturated fats

3. Lipids
Lipid = nonpolar, hydrophobic molecules that are made up of mostly carbon & hydrogen atoms
Contain a small amount of oxygen (sometimes N and/or P)
3 main types:
Fats
Phospholipids
Steroids
Used for energy storage, communication, & creation of the cell membrane

5. Fats Fats = lipids whose main function is energy storage
Also called triglyceride (triacylglycerol in textbook)
One glycerol molecule linked to 3 fatty acids

6. Unsaturated fats = one or more double bonds between carbons (ex
Unsaturated fats = one or more double bonds between carbons (ex. plant oils)
Are liquid at room temperature
Saturated fats = no double bonds between carbons (ex. lard, animal fats)
Are solid at room temperature
“Saturated” with hydrogen atoms
Copyright © 2003 Pearson Education, Inc. publishing Benjamin Cummings

7. Know What You’re Eating…
Trans fats = unsaturated fats that have hydrogens added to them to make them solid at room temperature
Hydrogenation causes the double bonds to rearrange, resulting in an isomer
Is associated with health risks

8. Function of Fats Long term energy storage
Act as cushioning for important organs
Act as insulation to maintain a stable body temperature

9. Phospholipids
Amphipathic = one end is hydrophilic & one end is hydrophobic
Phospholipid = lipids that make up the majority of the cell membrane
A glycerol attached to two fatty acids & one phosphate group
hydrophobic
hydrophilic

10. Cluster into a lipid bilayer to create the cell membrane
Hydrophobic tails arrange themselves inward, away from the watery environment
Hydrophilic heads are in contact with the watery environment & the cytoplasm of the cell
Keeps the inside of the cell separate from the external environment

11. Steroids
Steroid = lipid where the carbon skeleton is bent to form four fused rings
Function in cell communication
Cholesterol = “base steroid” from which your body produces other steroids
Example: testosterone & estrogen
Cholesterol is necessary to keep the cell membrane fluid
But too much can cause heart disease

12. (Don’t copy!) Other Steroids Are Made From Cholesterol

13. Other Lipids Waxes = a fatty acid linked to an alcohol
Very hydrophobic
Natural coating for fruits
Some insects & animals have waxy coats to prevent drying out
Carotenoids = orange & yellow plant pigments
Insoluble in water & have an oily consistency
Used in photosynthesis
Can be converted by animals to vitamin A & then retinal (used by eyes to detect light)