Lipids Section 3.3

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

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

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

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

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

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

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

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 http://www.biology.arizona.edu/cell_BIO/problem_sets/membranes/graphics/bilayer.jpg

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

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

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)