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CHAPTER 3 The Molecules of Life PowerPoint® Lectures for Essential Biology, Third Edition – Neil Campbell, Jane Reece, and Eric Simon Essential Biology with Physiology, Second Edition – Neil Campbell, Jane Reece, and Eric Simon Lectures by Chris C. Romero Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Biology and Society: Does Thanksgiving Dinner Make You Sleepy? • After finishing a huge Thanksgiving dinner, – Many people feel especially lethargic and a few even doze off. • Many people think that turkey makes you sleepy. – Is there a biological basis to this claim? Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings • Turkey meat is high in tryptophan. – Tryptophan is a molecule that is converted in your body to serotonin, which promotes sleep. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.1 • However, there is little evidence – That a turkey dinner encourages sleep more than any other meal. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Organic Molecules • A cell is mostly water. – The rest of the cell consists mostly of carbonbased molecules. – Organic chemistry is the study of carbon compounds. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Carbon Chemistry • Carbon is a versatile atom. – It has four electrons in an outer shell that holds eight. – Carbon can share its electrons with other atoms to form up to four covalent bonds. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Carbon can use its bonds to – Attach to other carbons. – Form an endless diversity of carbon skeletons. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.2 • The simplest organic compounds are hydrocarbons. – These are organic molecules containing only carbon and hydrogen atoms. – The simplest hydrocarbon is methane. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.3 • Larger hydrocarbons – Are the main molecules in the gasoline we burn in our cars. • The hydrocarbons of fat molecules provide energy for our bodies. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.4 • Each type of organic molecule has a unique threedimensional shape that defines its function in an organism. – The molecules of your body recognize one another based on their shapes. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • The unique properties of an organic compound depend not only on its carbon skeleton but also on the atoms attached to the skeleton. – These atoms are called functional groups. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.5 Giant Molecules from Smaller Building Blocks • On a molecular scale, many of life’s molecules are gigantic. – Biologists call them macromolecules. – Examples: DNA, carbohydrates Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Most macromolecules are polymers. – Polymers are made by stringing together many smaller molecules called monomers. – Cells link monomers by dehydration reactions. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.6a • Organisms also have to break down macromolecules. – Cells do this by a process called hydrolysis. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.6b Biological Molecules • There are four categories of large molecules in cells: – Carbohydrates – Lipids – Proteins – Nucleic acids Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Carbohydrates • Carbohydrates include: – Small sugar molecules in soft drinks – Long starch molecules in pasta and potatoes Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Monosaccharides • Monosaccharides are simple sugars. – Glucose is found in sports drinks. – Fructose is found in fruit. • Honey contains both glucose and fructose. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.7 • The monosaccharides glucose and fructose are isomers. – They have the same formula, but their atoms are arranged differently. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.8 • In aqueous solutions, monosaccharides form rings. • Monosaccharides are the main fuel that cells use for cellular work. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.9 Disaccharides • A disaccharide is a double sugar. – It is constructed from two monosaccharides. • Disaccharides are joined through a dehydration reaction. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.10 • Lactose is another type of disaccharide. – Some people have trouble digesting lactose, a condition called lactose intolerance. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.11 • The most common disaccharide is sucrose, common table sugar. – It consists of a glucose linked to a fructose. – Sucrose is extracted from sugar cane and the roots of sugar beets. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • The United States is one of the world’s leading markets for sweeteners. – The average American consumes about 64 kg of sugar per year. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.12 Polysaccharides • Complex carbohydrates are called polysaccharides. – They are long chains of sugar units. – They are polymers of monosaccharides. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.13 • One familiar example of a polysaccharide is starch. – Plant cells store starch for energy. – Potatoes and grains are major sources of starch in the human diet. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Animals store excess sugar in the form of a polysaccharide called glycogen. – Glycogen is similar in structure to starch. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Cellulose is the most abundant organic compound on Earth. – It forms cable-like fibrils in the tough walls that enclose plants. – It is a major component of wood. – It is also known as dietary fiber. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Most animals cannot derive nutrition from fiber. – Grazing animals survive on a diet of cellulose because they have prokaryotes in their digestive tracts that can break down cellulose. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.14 • Simple sugars and double sugars dissolve readily in water. – They are hydrophilic, or “water-loving.” Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Low-Carb Diets • In recent years, “low-carb diets” have become popular. – But consumers need to be wary of products boasting that they are “low-carb” because they can sometimes be unhealthy. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Lipids • Lipids are hydrophobic. – They do not mix with water. – Examples: fats and steroids Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fats • Dietary fat consists largely of the molecule triglyceride. – Triglyceride is a combination of glycerol and three fatty acids. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.15a • Fats perform essential functions in the human body: – Energy storage – Cushioning – Insulation Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Unsaturated fatty acids – Have less than the maximum number of hydrogens bonded to the carbons. • Saturated fatty acids – Have the maximum number of hydrogens bonded to the carbons. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.15b • Most animal fats have a high proportion of saturated fatty acids, which can be unhealthy. – Example: butter • Most plant oils tend to be low in saturated fatty acids. – Example: corn oil Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Not all fats are unhealthy. – Some fats perform important functions in the body and are essential to a healthy diet. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.16 Steroids • Steroids are very different from fats in structure and function. – The carbon skeleton is bent to form four fused rings. • Cholesterol is the “base steroid” from which your body produces other steroids. – Example: sex hormones Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.17 • Synthetic anabolic steroids are controversial. – They are variants of testosterone. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Some athletes use anabolic steroids to build up their muscles quickly. – However, these substances can pose serious health risks. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.18 Proteins • A protein is a polymer constructed from amino acid monomers. • Proteins perform most of the tasks the body needs to function. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.19 The Monomers: Amino Acids • All proteins are constructed from a common set of 20 kinds of amino acids. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Each amino acid consists of – A central carbon atom bonded to four covalent partners. – A side group that is variable among all 20. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.20 Proteins as Polymers • Cells link amino acids together by dehydration reactions. – The resulting bond between them is called a peptide bond. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.21 • Your body has tens of thousands of different kinds of protein. – The arrangement of amino acids makes each one different. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • Primary structure – The specific sequence of amino acids in a protein Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.22 • A slight change in the primary structure of a protein affects its ability to function. – The substitution of one amino acid for another in hemoglobin causes sickle-cell disease. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.23 Protein Shape • Proteins have four levels of structure. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.24 What Determines Protein Structure? • A protein’s shape is sensitive to the surrounding environment. – Unfavorable temperature and pH changes can cause a protein to unravel and lose its shape. – This is called denaturation. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Nucleic Acids • Nucleic acids are information storage molecules. – They provide the directions for building proteins. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • There are two types of nucleic acids: – DNA, deoxyribonucleic acid – RNA, ribonucleic acid Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings • The genetic instructions in DNA – Must be translated from “nucleic acid language” to “protein language.” Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.25 • Nucleic acids are polymers of nucleotides. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.26 • Each DNA nucleotide has one of the following bases: – Adenine (A) – Guanine (G) – Thymine (T) – Cytosine (C) Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.27 • Nucleotide monomers are linked into long chains. – These chains are called polynucleotides, or DNA strands. – A sugar-phosphate backbone joins them together. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.28a • Two strands of DNA join together to form a double helix. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.28b • RNA, ribonucleic acid, is different from DNA. – Its sugar has an extra OH group. – It has the base uracil (U) instead of thymine (T). Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Figure 3.29 Evolution Connection: DNA and Proteins as Evolutionary Tape Measures • Evolutionary relationships between organisms can be assessed. – Molecular genealogy extends to relationships between species. – Biologists use molecular analysis of DNA and protein sequences for testing evolutionary hypotheses. Copyright © 2007 Pearson Education, Inc. publishing as Pearson Benjamin Cummings Figure 3.30