Chapter 5 Lipids

Lipids Large biological molecules that do not form polymers Have little or no affinity for water – hydrophobic Consist mostly of hydrocarbons Include fats, phospholipids, steroids, waxes, and certain pigments Composed of a glycerol molecule and 3 fatty acids forming a triglyceride

Saturated Fats No double bonds between the carbons; therefore, the carbons are said to be “saturated” with hydrogens Include most animal fats Are solid at room temperature – lard and butter “hydrogenated vegetable oils” – such as peanut butter and margarine - are unsaturated fats that have been synthetically converted to saturated fats with the addition of hydrogen

Saturated Fats A diet rich in saturated fats contributes to the cardiovascular disease, atherosclerosis

Unsaturated Fats Have one or more double bonds Will have a “kink” in its tail where the double bonds occur Fats from plants and fish Usually liquid at room temperature (oils) The kinks caused by the double bonds prevent the fat from solidifying at room temperature

Importance of Fats Despite their negative “rap,” fats are important to living things Major function is storing energy 1 gram of fat stores over twice as much energy as 1 gram of polysaccharide (i.e. starch) In animals, fat also serves to cushion vital organs and fat under the skin insulates the body In marine mammals, such as seals and whales, fat makes up blubber

Phospholipids Have only 2 fatty acid tails instead of three A phosphate group is attached to the third hydroxyl group of the glycerol The tails are hydrophobic and the head is hydrophilic

Phospholipids In water, phospholipids arrange themselves so the hydrophobic tails do not touch water

Steroids A carbon skeleton consisting of four fused rings Example: cholesterol common component of animal cell membranes precursor from which other steroids are synthesized (i.e. sex hormones) too much in the blood can cause atherosclerosis