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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. Isomers L-Dopa 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. Disaccharides 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. Polysaccharides 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 Fats 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. Structural Proteins Receptor Proteins Storage Proteins Enzymes Contractile Proteins Hormonal Proteins Transport Proteins Sensory Proteins Defensive Proteins Gene Regulatory Proteins 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. Protein Structure Introduction Primary Protein Structure Secondary Protein Structure Tertiary Protein Structure Quaternary Protein 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. DNA and RNA Structure 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