UT Knoxville BIOL 140 - Chapter 6 (55 pages)

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CHAPTER 6 2011 Pearson Education Inc The Importance of Membranes The plasma membrane or cell membrane separates life from nonlife The plasma membrane separates the cell s interior from the external environment Membranes function to Keep damaging materials out of the cell Allow entry of materials needed by the cell Facilitate the chemical reactions necessary for life 2011 Pearson Education Inc Lipids What Is a Lipid Lipids are carbon containing compounds that are found in organisms and that are largely nonpolar and hydrophobic Hydrocarbons are nonpolar molecules that contain only carbon and hydrogen Lipids do not dissolve in water because they have a major hydrocarbon component called a fatty acid A fatty acid is a hydrocarbon chain bonded to a carboxyl COOH functional group Fatty acids and isoprene are the key building blocks of lipids 2011 Pearson Education Inc 2011 Pearson Education Inc Three Types of Lipids Found in Cells Lipid structure varies widely The three most important types of lipids found in cells 1 Fats are composed of three fatty acids linked to glycerol Also called triacylglycerols or triglycerides 2 Steroids are a family of lipids with a distinctive four ring structure Cholesterol is an important steroid in mammals 3 Phospholipids consist of a glycerol linked to a phosphate group PO42 and to either two chains of isoprene or two fatty acids 2011 Pearson Education Inc 2011 Pearson Education Inc The Structure of Membrane Lipids Membrane forming lipids contain both a polar hydrophilic region and a nonpolar hydrophobic region Phospholipids are amphipathic The head region consisting of a glycerol a phosphate and a charged group contains highly polar covalent bonds The tail region is comprised of two nonpolar fatty acid or isoprene chains When placed in solution the phospholipid heads interact with water while the tails do not allowing these lipids to form membranes 2011 Pearson Education Inc 2011 Pearson Education Inc Phospholipids and Water Phospholipids