Biology Chapter 1 part 2.pdf

Concept 1.3: Lipids are a diverse group of hydrophobic molecules § Lipids are the one class of large biological molecules that does not include true polymers § The unifying feature of lipids is being hydrophobic: they mix poorly (little or no affinity), with water § Consist mostly of hydrocarb...

Concept 1.3: Lipids are a diverse group of hydrophobic molecules § Lipids are the one class of large biological molecules that does not include true polymers § The unifying feature of lipids is being hydrophobic: they mix poorly (little or no affinity), with water § Consist mostly of hydrocarbon regions § Hydrocarbon: Hydrogen and carbon meaning they are nonpolar. § Likes dissolve likes. © 2017 Pearson Education, Inc.  Most biologically important lipids are of three main types: (1) Fats (2) Phospholipids (3) Steroids © 2017 Pearson Education, Inc.  Most biologically important lipids are of three main types: (1) Fats (2) Phospholipids (3) Steroids © 2017 Pearson Education, Inc.  Fats § Fats are constructed from two types of smaller molecules (monomers): (1) A single glycerol molecule and (2) Three fatty acids © 2017 Pearson Education, Inc. Fats § 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 hydrocarbon skeleton © 2017 Pearson Education, Inc. © 2017 Pearson Education, Inc. © 2017 Pearson Education, Inc. § Hydrocarbon and carboxyl group (the same in all fatty acids) § 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 and no double bonds § Unsaturated fatty acids have one or more double bonds © 2017 Pearson Education, Inc. © 2017 Pearson Education, Inc.  (a) Saturated fat Structural formula of a saturated fat molecule Space-filling model of stearic acid, a saturated fatty acid (b) Unsaturated fat Structural formula of an unsaturated fat molecule Space-filling model of oleic acid, an unsaturated fatty acid Cis double bond causes bending. The Synthesis and Breakdown of Fats Figure 5.9a H Hydroxyl H2O Fatty acid (in this case, palmitic acid) Carboxyl group Glycerol (a) One of three dehydration reactions in the synthesis of a fat © 2017 Pearson Education, Inc. § In a fat, three fatty acids are joined to glycerol by an ester linkage, creating a triacylglycerol, or triglyceride § The fatty acids in a fat can be all the same or of two or three different kinds § Fats the same as triacylglycerols the same as triglycerides. © 2017 Pearson Education, Inc. Figure 5.9b Ester linkage (b) Fat molecule (triacylglycerol) © 2017 Pearson Education, Inc. § Fats separate from water because water molecules hydrogen-bond to each other and exclude the fats © 2017 Pearson Education, Inc. § 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 and fish fats are usually unsaturated © 2017 Pearson Education, Inc. § A diet rich in saturated fats may contribute to cardiovascular disease through plaque deposits § Hydrogenation: is the process of converting unsaturated fats to saturated fats by adding hydrogen § Hydrogenating vegetable oils also creates unsaturated fats with trans double bonds § These trans fats may contribute more than saturated fats to cardiovascular disease © 2017 Pearson Education, Inc. § The major function of fats is energy storage § Humans and other mammals store their long- term food reserves in adipose cells § Adipose tissue also cushions vital organs and insulates the body © 2017 Pearson Education, Inc. Figure 5.9b Ester linkage (b) Fat molecule (triacylglycerol)  Most biologically important lipids are of three main types: (1) Fats (2) Phospholipids (3) Steroids © 2017 Pearson Education, Inc.  Phospholipids § In a phospholipid, two fatty acids and a phosphate group are attached to glycerol § Phospholipid are amphipathic molecules § The two fatty acid tails are hydrophobic, but the phosphate group and its attachments form a hydrophilic head Hydrophilic head Hydrophobic tails © 2017 Pearson Education, Inc. (c) Phospholipid symbol Figure 5.11 Choline Hydrophilic Hydrophilic head head Phosphate Hydrophilic Hydrophobic tails head Glycerol (c) Phospholipid symbol Hydrophobic tails Fatty acids Hydrophobic tails Kink due to cis (c) Phospholipid symbol double bond (a) Structural formula (b) Space-filling model § When phospholipids are added to water, they self-assemble into double-layered sheets called bilayers, with the hydrophobic tails pointing toward the interior (d) Phospholipid bilayer © 2017 Pearson Education, Inc. § At the surface of a cell, phospholipids are also arranged in a bilayer § This bilayer forms a boundary between the cell and its external environment © 2017 Pearson Education, Inc.  Most biologically important lipids are of three main types: (1) Fats (2) Phospholipids (3) Steroids © 2017 Pearson Education, Inc.  Steroids § Steroids are lipids characterized by a carbon skeleton consisting of four fused rings § Cholesterol, a type of steroid, is a component in animal cell membranes and a precursor from which other steroids are synthesized § A high level of cholesterol in the blood may contribute to cardiovascular disease © 2017 Pearson Education, Inc. Figure 5.12 Cholesterol Lipids § Fats (Triglycerols, Triglycerides) § Phospholipids § Steroids