Overview The Molecules of Life All living things are made up of four classes of large biological molecules carbohydrates lipids proteins and nucleic acids Within cells small organic molecules are joined together to form larger molecules Macromolecules are large molecules composed of thousands of covalently connected atoms Each cell has thousands of different kinds of macromolecules Macromolecules vary among cells of an organism vary more within a species and vary even more between species Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Concept 5 1 Macromolecules are polymers built from monomers A polymer is a long molecule consisting of many similar building blocks These small building block molecules are called monomers An immense variety of polymers can be built from a small set of monomers Three of the four classes of life s organic molecules are polymers Carbohydrates Proteins Nucleic acids Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings The Synthesis and Breakdown of Polymers A condensation reaction or more specifically a dehydration reaction occurs when two monomers bond together through the loss of a water molecule Enzymes are macromolecules that speed up the dehydration process Polymers are disassembled to monomers by hydrolysis a reaction that is essentially the reverse of the dehydration reaction Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Fig 5 2 HO 1 2 3 H Short polymer HO Unlinked monomer Dehydration removes a water molecule forming a new bond HO 2 1 H 3 H2O 4 H Longer polymer a Dehydration reaction in the synthesis of a polymer HO 1 2 3 4 Hydrolysis adds a water molecule breaking a bond HO 1 2 3 b Hydrolysis of a polymer H H H2O HO H Concept 5 2 Carbohydrates serve as fuel and building material Carbohydrates include sugars and the polymers of sugars The simplest carbohydrates are monosaccharide s or single sugars Carbohydrate macromolecules are polysaccharides polymers composed of many sugar building blocks 1 Monosaccharide s Monosaccharide s have molecular formulas that are usually multiples of CH2O Glucose C6H12O6 is the most common monosaccharide Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Monosaccharide s are classified by The location of the carbonyl group as aldose or ketose The number of carbons in the carbon skeleton Monosaccharide s serve as a major fuel for cells and as raw material for building molecules A disaccharide is formed when a dehydration reaction joins two monosaccharides This covalent bond is called a glycosidic linkage Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings s e d i r ha c c a Trioses C H O os Fig 5 3 Aldoses 3 6 3 Pentoses C5H10O5 Hexoses C6H12O6 Glyceraldehyde Ribose Glucose Ketoses Mon Galactose Dihydroxyacetone Ribulose Fructose Polysaccharides Polysaccharides the polymers of sugars have storage and structural roles The structure and function of a polysaccharide are determined by its sugar monomers and the positions of glycosidic linkages Two major kinds of polysaccharide s 1 Storage Polysaccharides 2 Structural Polysaccharides Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Storage Polysaccharides Starch a storage polysaccharide of plants consists entirely of glucose monomers Plants store surplus starch as granules within chloroplasts and other plastids Glycogen is a storage polysaccharide in animals Humans and other vertebrates store glycogen mainly in liver and muscle cells Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Fig 5 6 Chloroplast Mitochondria Glycogen granules Starch 0 5 m 1 m Glycogen Amylose Amylopectin a Starch a plant polysaccharide b Glycogen an animal polysaccharide Structural Polysaccharides The polysaccharide Cellulose is a major component of the tough wall of plant cells Like starch cellulose is a polymer of glucose but the glycosidic linkages differ The difference is based on two ring forms for glucose alpha and beta Chitin another structural polysaccharide is found in the exoskeleton of arthropods Chitin also provides structural support for the cell walls of many fungi Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Fig 5 7 Polymers with glucose are helical Polymers with glucose are straight a and glucose ring structures Glucose b Starch 1 4 linkage of glucose monomers Glucose b Cellulose 1 4 linkage of glucose monomers In straight structures H atoms on one strand can bond with OH groups on other strands Parallel cellulose molecules held together this way are grouped into microfibrils which form strong building materials for plants Enzymes that digest starch by hydrolyzing linkages can t hydrolyze linkages in cellulose Cellulose in human food passes through the digestive tract as insoluble fiber Some microbes use enzymes to digest cellulose Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Fig 5 8 Cell walls Cellulose microfibrils in a plant cell wall Microfibril 10 m 0 5 m Cellulose molecules Glucose monomer Fig 5 10 Chitin a The structure of the chitin monomer b Chitin forms the exoskeleton of arthropods c Chitin is used to make a strong and flexible surgical thread Concept 5 3 Lipids are a diverse group of hydrophobic molecules Lipids are the one class of large biological molecules that do not form polymers The unifying feature of lipids is having little or no affinity for water Lipids are hydrophobic because they consist mostly of hydrocarbons which form nonpolar covalent bonds The most biologically important lipids are 1 Fats 2 Phospholipids 3 Steroids Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings 1 Fats Fats are constructed from two types of smaller molecules glycerol and 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 Fats separate from water because water molecules form hydrogen bonds with each other and exclude the fats In a fat three fatty acids are joined to glycerol by an ester linkage creating a triacylglycerol or triglyceride Copyright 2008 Pearson Education Inc publishing as Pearson Benjamin Cummings Fig 5 11a Fatty acid palmitic acid Glycerol a Dehydration reaction in the synthesis of a fat Fig 5 11b Ester linkage b Fat molecule triacylglycerol Fatty acids vary in length number