Section C: Lipids - Diverse Hydrophobic Molecules CHAPTER 5 THE STRUCTURE AND FUNCTION OF MACROMOLECULES HW 1-4 Section C: Lipids - Diverse Hydrophobic Molecules 1. Fats store large amounts of energy 2. Phospholipids are major components of cell membranes 3. Steroids include cholesterol and certain hormones Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Properties of Lipids Lipids are NOT POLYMERS Lipids are HIGHLY DIVERSE in STRUCTURE and FUNCTION HYDROPHOBIC- Lipids have little or no affinity for water

USES OF FAT: INSULATION

Uses of Fat: Long-Term Energy Storage FAT CONTAINS ABOUT 2X AS MUCH ENERGY PER GRAM AS SUGAR “FAT RICH” Bear about to hibernate for winter “Svelte” Spring Time Look (After living off stored fat reserves over the winter)

Storing Energy in Plants vs Animals Animals need to be light to move fast! Fat = low density but high energy content, i.e. small mass and volume stores a lot of energy. (Optimize ratio of muscle to fat) Plants are anchored in one place. Energy can be stored primarily in starch. Plants tend to have much lower fat content.

USES OF FAT: CELL MEMBRANES (form compartments in cells) HORMONES AND STERIODS – chemical regulation VITAMIN STORAGE – some vitamins are only soluble in fat tissue.

STRUCTURE OF FATTY ACIDS Hydrocarbon chain = Energy rich Carboxylic Acid Group Fatty Acids Can Vary in LENGTH AND SHAPE

What key bonding feature causes the shapes of these two fatty acids to be different? The presence of double bonds can cause kinks in the hydrocarbon chain.

The kinks in a hydrocarbon chain are the result of the lack of free rotation around a C= C double bond

Link to Sigma and Pi Bonds (Show ethylene only) Double bonds are formed by a sigma (straight-on overlap) and a pi bond (overlap of parallel p – orbitals)

Cis and Trans Isomers Geometric isomers produced by double bond

Extension: Cis-Trans isomerization is a key part of the chemistry of vision Link to Vision animation

H bonds to C at every possible position Fig. 5-12 SATURATED FATS All C-C single bonds H bonds to C at every possible position Structural formula of a saturated fat molecule Stearic acid, a saturated fatty acid Video link sat vs unsaturated (a) Saturated fat UNSATURATED FATS May contains kinks or bends due to lack of free rotation around C=C double bonds Figure 5.12 Examples of saturated and unsaturated fats and fatty acids Structural formula of an unsaturated fat molecule Oleic acid, an unsaturated fatty acid (b) Unsaturated fat cis double bond causes bending

Cis and Trans Fatty Acids

Cis Fatty Acids Have Bent Shape; Trans-Fatty Acids are more linear

Carbons opposite sides of C=C bond Carbons Same side of C=C bond

IB MEMORIZE THIS RXN FOR TEST!