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INTRODUCTORY CHEMISTRY Concepts and Critical Thinking Sixth Edition by Charles H. Corwin Chapter 20 Biochemistry by Christopher Hamaker © 2011 Pearson Education, Inc. Chapter 20 1 Introduction to Biochemistry • There are 30 elements that are essential for life. • The study of the chemistry of living things is called biochemistry. • Biological compounds are often large and complex with molar masses greater than 1,000,000 g/mol. • These large molecules are polymers of smaller molecules. © 2011 Pearson Education, Inc. Chapter 20 2 Biological Compounds © 2011 Pearson Education, Inc. Chapter 20 3 Proteins • Proteins are naturally occurring polymers composed of many amino acids. • An amino acid has both an amine and a carboxylic acid functional group. • Amino acids are linked together by amide bonds, which are referred to as peptide linkages. © 2011 Pearson Education, Inc. Chapter 20 4 Carbohydrates • A carbohydrate is either a simple sugar or a polymer composed of many simple sugars. • A carbohydrate usually contains either an aldehyde or ketone functional group and several alcohol groups. • Starch is a carbohydrate polymer composed of glucose units linked together by glycoside linkages. © 2011 Pearson Education, Inc. Chapter 20 5 Lipids • A lipid is a water-insoluble compound usually composed of an alcohol and one or more carboxylic acid molecules. • Fats and oils are esters of glycerol, an alcohol that has three –OH groups. • As a result, each molecule of a fat or an oil contains three ester groups from three carboxylic acid molecules joined to one glycerol molecule. © 2011 Pearson Education, Inc. Chapter 20 6 Nucleic Acids • A nucleic acid is a biochemical polymer composed of a very large number of individual units. • Each unit in the nucleic acid contains a sugar molecule attached to an organic nitrogen-containing molecule and an attached phosphate group. • The units are attached together by phosphate linkages. © 2011 Pearson Education, Inc. Chapter 20 7 Amino Acids • Proteins are composed of amino acids. • An amino acid has an amine (–NH2) and a carboxyl group (–COOH) attached to a carbon atom with a side chain (R–) attached to the acarbon. • There are 20 naturally occurring amino acids in human proteins. Each one has a different side chain (R–). © 2011 Pearson Education, Inc. Chapter 20 8 The 20 Natural Amino Acids Neutral Amino Acids Acidic Amino Acids Basic Amino Acids © 2011 Pearson Education, Inc. Chapter 20 9 Primary Structure of Proteins • Proteins are polypeptides composed of hundreds or thousands of amino acid units (amide bonds). • The primary structure of a protein is the sequence of amino acids. Individual amino acids are represented by the ovals in the figure below. • The replacement of one amino acid by another in the primary structure of a protein can completely alter its biological activity. © 2011 Pearson Education, Inc. Chapter 20 10 Secondary Structure of Proteins • When the peptide chain twists and bends, proteins acquire a secondary structure. • There are two primary types of secondary structure: a-helix and pleated sheet. • An a-helix is analogous to that in a coiled telephone cord. © 2011 Pearson Education, Inc. Chapter 20 11 Pleated Sheet • In a pleated sheet, the chains run antiparallel to each other. It looks like a sheet of paper folded in an accordion shape. • Secondary structures in proteins are a result of hydrogen bonds. © 2011 Pearson Education, Inc. Chapter 20 12 Tertiary Structure of Proteins • The overall three-dimensional structure of a protein is referred to as its tertiary structure. • The tertiary structure of a protein may be long and extended, or compact and folded. • The tertiary structure of a protein is held together by intermolecular forces. © 2011 Pearson Education, Inc. Chapter 20 13 Enzymes • An enzyme is a protein that acts as a biological catalyst. • Enzymes are incredibly selective for specific molecules. • An enzyme can speed up a biochemical reaction so that the rate is a million times faster than it would be in the absence of the enzyme. • Many reactions catalyzed by enzymes would be too slow without the enzyme to sustain life. © 2011 Pearson Education, Inc. Chapter 20 14 Enzyme Mechanisms • The location where the reaction occurs on the enzyme is called the active site. • The molecule that reacts is the substrate. • We can use the lock-and-key model to describe enzyme mechanisms. • In the model, the key is the enzyme and the lock is the substrate. © 2011 Pearson Education, Inc. Chapter 20 15 Enzyme Reactions • An enzyme reaction takes place in two steps. • First, the substrate (S) binds to the active site on the enzyme (E). Step 1: E + S → ES • Second, the enzyme releases two or more products (P1 and P2). Step 2: © 2011 Pearson Education, Inc. ES → E + P1 + P2 Chapter 20 16 Enzyme Reactions, Continued • The active site of an enzyme has a shape specifically designed to bind its substrate. • Once the reaction has occurred, the active site is free to bind to another substrate molecule and repeat the reaction. © 2011 Pearson Education, Inc. Chapter 20 17 The Enzyme Ptyalin • The enzyme ptyalin is in human saliva and catalyzes the breaking down of starch molecules into sugar units. • The reaction would take about two years to occur without the enzyme. © 2011 Pearson Education, Inc. Chapter 20 18 Carbohydrates • The word carbohydrate means “hydrates of carbon,” and many have the empirical formula CH2O. • Carbohydrate names usually end in the suffix -ose. • Carbohydrates have an aldehyde or ketone functional group and several hydroxyl groups. © 2011 Pearson Education, Inc. Chapter 20 19 Simple Sugars • A simple sugar molecule typically has three to six carbons, an aldehyde or ketone group, and a few hydroxyl groups. • A monosaccharide with an aldehyde group is an aldose, and one with a ketone group is a ketose. © 2011 Pearson Education, Inc. Chapter 20 20 Aqueous Structures of Sugars • In aqueous solution, sugar molecules usually exist in ring structures. • Glucose forms a cyclic structure by joining a hydroxyl group to an aldehyde group. • The resulting ring structure has five carbon atoms and one oxygen atom. © 2011 Pearson Education, Inc. Chapter 20 21 Disaccharides • A disaccharide is two monosaccharide molecules joined together. • In the formation of a disaccharide, two simple sugars split out water and are joined together by a special –O– bond called a glycoside linkage. © 2011 Pearson Education, Inc. Chapter 20 22 Polysaccharides • A polysaccharide is a polymer of many monosaccharide linkages joined by glycoside linkages. • Starch and cellulose are both polysaccharides composed only of glucose units, but with slightly different three-dimentional structures. © 2011 Pearson Education, Inc. Chapter 20 23 Lipids • Unlike most other biological compounds, lipids are not water soluble. • Lipids include: – Fats and oils – Waxes – Steroids – Water-insoluble vitamins A, D, E, and K © 2011 Pearson Education, Inc. Chapter 20 24 Fatty Acids • A fatty acid is a carboxylic acid with a long hydrocarbon chain. • Fatty acids can be saturated or unsaturated. © 2011 Pearson Education, Inc. Chapter 20 25 Triglycerides (Triglycerols) • A triglyceride is a lipid formed from glycerol, a trihydroxy alcohol, and three fatty acids. • When three fatty acids react with glycerol, a triglyceride is formed with three ether linkages. © 2011 Pearson Education, Inc. Chapter 20 26 Fats • In triglycerides obtained from animals, the fatty acids are mostly saturated and have few double bonds. • A semisolid lipid obtained from an animal source is a fat. • The following structure is an example of a saturated triglyceride from animal fat. © 2011 Pearson Education, Inc. Chapter 20 27 Oils • A liquid lipid obtained from a plant source is an oil. • Triglycerides obtained from plants have mostly unsaturated fatty acid chains. • The following structure is an example of an unsaturated triglyceride from a vegetable oil. © 2011 Pearson Education, Inc. Chapter 20 28 Nucleic Acids • • • Nucleic acids are biochemical compounds found in every living cell. Nucleic acids contain the genetic information responsible for the reproduction of a species. There are two basic types of nucleic acids: 1. Deoxyribonucleic acid (DNA) 2. Ribonucleic acid (RNA) • A nucleic acid is a polymer composed of many repeating units, each of which is called a nucleotide. © 2011 Pearson Education, Inc. Chapter 20 29 Nitrogen Bases • There are five nitrogen bases. • Three are found in both DNA and RNA, one is found only in DNA, and one is found only in RNA. • Their structures are shown below: © 2011 Pearson Education, Inc. Chapter 20 30 DNA and RNA • DNA and RNA are polymers of individual nucleotides. A segment is shown here. • A DNA molecule is actually two strands of DNA wound together in a spiral structure called a double helix. • The double strand is held together by hydrogen bonds between nitrogen pairs. © 2011 Pearson Education, Inc. Chapter 20 31 DNA Double Helix • An adenine (A) on one strand always hydrogen bonds to a thymine (T) on the other strand. • Also, a cytosine (C) on one strand always hydrogen bonds to a guanine (G) on the other strand. • These interactions give DNA its characteristic structure. © 2011 Pearson Education, Inc. Chapter 20 32 Chapter Summary • There are four major types of biological molecules: 1. A protein is composed of amino acids. 2. A carbohydrate is composed of simple sugar molecules. 3. A lipid is a water-insoluble biological molecule. 4. A nucleic acid is a polymer composed of a sugar molecule, a nitrogen base, and a phosphoric acid. © 2011 Pearson Education, Inc. Chapter 20 33 Chapter Summary, Continued • An enzyme is a catalyst for biological reactions. • Enzymes work by a lock-and-key mechanism, where only a specific substrate fits into the enzyme to react. • Reactions catalyzed by enzymes can be completed in a matter of seconds, whereas the reaction would normally take many years. © 2011 Pearson Education, Inc. Chapter 20 34 Chapter Summary, Continued • A triglyceride is an ester of glycerol and three different fatty acids. • A fat is a triglyceride from an animal source. An oil is a triglyceride from a plant source. • A nucleic acid is a molecule that carries genetic information. • DNA and RNA are the two basic types of nucleic acids. © 2011 Pearson Education, Inc. Chapter 20 35