Chapter 5-Lipids (1).ppt

Chapter 5/Lipids The Structure and Function of Large Biological Molecules PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishi...

Chapter 5/Lipids The Structure and Function of Large Biological Molecules PowerPoint® Lecture Presentations for Biology Eighth Edition Neil Campbell and Jane Reece Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Lipids •A class of organic compounds that are fatty acids or their derivatives and are insoluble in water but soluble in organic solvents. •Lipids Do not Form Polymers Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Lipids are Hydrophobic • A hydrophobic molecule is a molecule that won't combine with water. • Lipids are hydrophobic because they consist mostly of hydrocarbons, which form nonpolar covalent bonds Important Lipids • The most biologically important lipids are • 1) Fats, • 2) Phospholipids • 3) Steroids Fats • Fats are also known as triglycerides, molecules made from the combination of one molecule of glycerol with three fatty acids Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Glycerol plus Fatty Acids • Glycerol is a three-carbon alcohol with a hydroxyl group attached to each carbon • A fatty acid consists of a carboxyl group attached to a long carbon skeleton Glycerol Fatty Acids Fat: Glycerol with Three Fatty Acids Fig. 5-11 Fatty acid (palmitic acid) Glycerol (a) Dehydration reaction in the synthesis of a fat Ester linkage (b) Fat molecule (triacylglycerol) • Fats separate from water because water molecules form hydrogen bonds with each other and exclude the fats Fat is Hydrophobic (Water Fearing) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • Fatty acids vary in length (number of carbons) and in the number and locations of double bonds • Saturated fatty acids have the maximum number of hydrogen atoms possible and no double bonds • Unsaturated fatty acids have one or more double bonds Animation: Fats Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 5-12 Structural formula of a saturated fat molecule Stearic acid, a saturated fatty acid (a) Saturated fat Structural formula of an unsaturated fat molecule Oleic acid, an unsaturated fatty acid (b) Unsaturated fat cis double bond causes bending cis double bond causes bending • Fats made from saturated fatty acids are called saturated fats, and are solid at room temperature • Most animal fats are saturated • Fats made from unsaturated fatty acids are called unsaturated fats or oils, and are liquid at room temperature • Plant fats and fish fats are usually unsaturated Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • A diet rich in saturated fats may contribute to cardiovascular disease through plaque deposits (atherosclerosis). • Hydrogenation is the process of converting unsaturated fats to saturated fats by adding H (peanut butter, margarine) • Hydrogenating vegetable oils also creates unsaturated fats with trans double bonds. • These trans fats may contribute more than saturated fats to cardiovascular disease Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings • The major functions of Fats are: • Energy storage (Adipose Cells). • Vitamin Absorption • Adipose tissue also cushions vital organs and insulates the body sustaining a normal body temperature Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Phospholipids • In a phospholipid, two fatty acids and a phosphate group are attached to glycerol • The two fatty acid tails are hydrophobic (Water Fearing), but the phosphate group and its attachments form a hydrophilic (Water Loving)head. • Phospholipids are the major component of all cell membranes forming the phospholipid bilayer of the plasma membrane. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Hydrophobic tails Hydrophilic head Fig. 5-13 (a) Structural formula Choline Phosphate Glycerol Fatty acids Hydrophilic head Hydrophobic tails (b) Space-filling model (c) Phospholipid symbol • When phospholipids are added to water, The cell membrane consists of two adjacent layers of phospholipids, which form a bilayer. The fatty acid tails of phospholipids face inside, away from water, whereas the phosphate heads face the outward aqueous side. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Plasma Membrane Fig. 5-14 Hydrophilic head Hydrophobic tail WATER WATER Phospholipids in Plasma Membrane Steroids • Steroids are lipids characterized by a carbon skeleton consisting of four fused rings • Cholesterol, an important steroid, is a component in animal cell membranes • Although cholesterol is essential in animals, high levels in the blood may contribute to cardiovascular disease Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings Fig. 5-15