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Chapter 2 Atoms, Molecules, and Life Lectures by Gregory Ahearn University of North Florida Copyright © 2009 Pearson Education, Inc.. 2.1 What Are Atoms? Elements: substances that can neither be broken down nor converted to other substances (e.g., carbon) Copyright © 2009 Pearson Education Inc. 2.1 What Are Atoms? Atoms: basic structural unit of matter; made up of subatomic particles • Atomic nucleus (central part of the atom) • Protons (positive charge) • Neutrons (neutral charge) • Electrons (negative charge) Atomic number: the number of protons in the nucleus • Is unique for each element • 92 different elements have been described. Copyright © 2009 Pearson Education Inc. 2.1 What Are Atoms? Hydrogen and helium have the simplest atomic structure. • Hydrogen has one proton and one electron. • Helium has two protons, two neutrons, and two electrons. e e- p+ p+ p+ (a) Hydrogen (H) Copyright © 2009 Pearson Education Inc. n n atomic nucleus e(b) Helium (He) Fig. 2-1 2.1 What Are Atoms? Atoms of the same element with different numbers of neutrons are called isotopes of the element. Some isotopes spontaneously break apart, forming different kinds of atoms and releasing energy in the process. Such isotopes are radioactive. Example: radioactive uranium isotopes decay and form lead in the process Copyright © 2009 Pearson Education Inc. 2.1 What Are Atoms? PLAY Animation—Atomic Structure Copyright © 2009 Pearson Education Inc. 2.1 What Are Atoms? Electron shells: electrons orbit around atomic nuclei at specific distances, called electron shells. Different atoms have different electron shells: • The inner shell only has two electrons. • The second shell holds up to eight electrons. • Additional shells hold up to eight electrons. Copyright © 2009 Pearson Education Inc. 2.1 What Are Atoms? The first four atomic electron shells • • • • Carbon (C) Oxygen (O) Phosphorus (P) Calcium (Ca) 2e8e- 4e- 6e- 5e8e- 2e- 2e- 2e- 2e- 6p+ 6n 8p+ 8n 15p+ 16n 20p+ 20n Carbon (C) C Oxygen (O) O Phosphorus (P) P 8e- Calcium (Ca) Ca Fig. 2-2 Copyright © 2009 Pearson Education Inc. 2.1 What Are Atoms? Electrons can move from electron shell to electron shell. • Electrons move from an inner to an outer shell when absorbing energy. • Electrons move from an outer shell to an inner shell when releasing energy. Copyright © 2009 Pearson Education Inc. 2 1 An electron absorbs energy The energy boosts the electron to a higher-energy shell energy – – + + 3 The electron drops back into lower-energy shell, releasing energy as light light – + Fig. 2-3 2.2 How Do Atoms Form Molecules? Molecules: two or more atoms of one or more elements held together by interactions among their outermost electron shells • Atoms interact with one another according to two basic principles: • An inert atom will not react with other atoms when its outermost electron shell is completely full or empty. • A reactive atom will react with other atoms when its outermost electron shell is only partially full. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules? Atoms combine with each other to fill outer electron shells (e.g. hydrogen and oxygen have unfilled outer electron shells, and thus, can combine to form the water molecule). The water molecule, with a filled outer electron shell, is more stable than either the hydrogen or oxygen atoms that gave rise to it. The results of losing, gaining, or sharing electrons are chemical bonds—attractive forces that hold atoms together in molecules. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules? PLAY Animation—Biologically Important Atoms Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules? A molecule may be depicted in different ways. H H H H H C C C C H H H H O H (a) All bonds shown CH3 CH2 CH2 CH2 OH (b) Bonds within common groups omitted OH (c) Carbons and their attached hydrogens omitted (d) Overall shape depicted Copyright © 2009 Pearson Education Inc. Fig. 2-4 2.2 How Do Atoms Form Molecules? Types of bonds • Ionic bonds: formed by passing an electron from one atom to another • One partner becomes positive, the other negative, and they attract one another. • Na+ + Cl– becomes NaCl (sodium chloride) • Positively or negatively charged atoms are called ions. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules? Sodium atom (neutral) Chlorine atom (neutral) – Charged atoms interact to form ionic bonds. • Positively charged atoms • Negatively charged atoms – – – – – – – – – 11p+ 11n – – – – – – – – – – – – 17p+ 18n – – – – – Electron transferred (a) Neutral atoms Sodium ion (+) Chloride ion (–) – – – – – – – – – – 11p+ 11n – – – – – (b) Ions – – – – – – – – 17p+ 18n – Copyright © 2009 Pearson Education Inc. – – – – – Attraction between opposite charges (c) An ionic compound: NaCl Cl- Na+ Cl- Na+ Cl- Na+ Cl- Na+ Cl- Fig. 2-5 2.2 How Do Atoms Form Molecules? PLAY Animation—Ionic Bonds Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules? Types of bonds (continued) • Covalent bonds: bond between two atoms that share electrons in their outer electron shell • For example, an H atom can become stable by sharing its electron with another H atom, forming H2 gas. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules? Covalent bonds produce either nonpolar or polar molecules. • Nonpolar molecule: atoms in a molecule equally share electrons that spend equal time around each atom, producing a nonpolar covalent bond Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules? Nonpolar covalent bonding in hydrogen Same charge on both nuclei + – – (uncharged) + Electrons spend equal time near each nucleus (a) Nonpolar covalent bonding in hydrogen Fig. 2-6a Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules? Covalent bonds produce either nonpolar or polar molecules (continued). • Polar molecules: atoms in a bond unequally share electrons, producing a polar covalent bond • One atom in the bond has a more positive charge in the nucleus, and so attracts electrons more strongly, becoming the negative pole of the molecule. • The atom in the bond that has a less positive charge in the nucleus gives up electrons, becoming the positive pole of the molecule. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules? Polar covalent bonding in water (oxygen: slightly negative) (–) – – – – – – Larger positive charge – 8p+ 8n – Electrons spend more time near the larger nucleus – – + + Smaller positive charge (hydrogens: slightly positive) (+) (+) (b) Polar covalent bonding in water Fig. 2-6b Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules? PLAY Animation—Covalent Bonds Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules? Types of bonds (continued) • Hydrogen bonds: weak electrical attraction between positive and negative parts of polar molecules • Example: the negative charge of oxygen atoms in water molecules attract the positive charge of hydrogen atoms in other water molecules Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules? Hydrogen bonds H (+) O (–) H (+) H (+) O (–) H (+) hydrogen bonds Fig. 2-7 Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules? PLAY Animation—Introducing Water’s Properties Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules? Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life? Water interacts with many other molecules. • Oxygen released by plants during photosynthesis comes from water. • Water is used by animals to digest food. • Water is produced in chemical reactions that produce proteins, fats, and sugars. Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life? Many molecules dissolve easily in water. • Water is an excellent solvent, capable of dissolving a wide range of substances because of its positive and negative poles. NaCl dropped into H2O • The positive end of H2O is attracted to Cl–. • The negative end of H2O is attracted to Na+. • These attractions tend to push apart the components of the original salt. Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life? Water as a solvent Cl– Na+ H Na+ Cl– H O Cl– Na+ Fig. 2-8 Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life? PLAY Animation—Solvent Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life? Water molecules tend to stick together. • Surface tension: water tends to resist being broken • Cohesion: water molecules stick together Fig. 2-9 Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life? PLAY Animation—High Cohesion Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life? Water can form ions. • Water spontaneously becomes H+ and OH–. • Acid solutions have a lot of H+ (protons). • Alkaline solutions have a lot of OH– (hydroxyl ions). • A base is a substance that combines with H+, reducing their numbers. • pH measures the relative amount of H+ and OH– in a solution. Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life? A water molecule is ionized. (–) O H O H water (H2O) (+) + H H hydroxide ion (OH–) hydrogen ion (H+) Fig. 2-10 Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life? pH measures acidity. • • • • Acids have a pH below 7. Bases have a pH above 7. Neutral solutions have a pH of 7. Buffers are substances that maintain a constant pH in a solution. Copyright © 2009 Pearson Education Inc. 0 100 1 10–1 2 10–2 3 pH value 10–3 Copyright © 2009 Pearson Education Inc. 10–4 5 10–5 H+ 6 10–6 7 10–7 8 10–8 (H+ > OH–) 10–9 increasingly acidic 10 10–10 11 10–11 12 10–12 13 10–13 drain cleaner (14.0) 1 molar sodium hydroxide (NaOH) oven cleaner (13.0) household ammonia (11.9) washing soda (12) phosphate detergents chlorine bleach (12.6) toothpaste (9.9) seawater (7.8–8.3) baking soda (8.4) water from faucet milk (6.4) pure water (7.0) blood, sweat (7.4) normal rain (5.6) urine (5.7) black coffee (5.0) orange (3.5) tomatoes beer (4.1) vinegar, cola (3.0) stomach acid (2) lemon juice (2.3) 1 molar hydrochloric acid (HCl) 2.3 Why Is Water So Important To Life? The pH scale 4 9 14 neutral (H+ = OH–) (H+ < OH–) 10–14 increasingly basic concentration in moles/liter Fig. 2-11 2.3 Why Is Water So Important To Life? PLAY Animation—pH Scale Copyright © 2009 Pearson Education Inc. 2.4 Why Is Carbon So Important To Life? Carbon can combine with other atoms in many ways to form a huge number of different molecules. This is possible because carbon has four electrons in its outermost shell, leaving room for four more electrons from other atoms. Therefore, carbon can form many bonds with other atoms. Copyright © 2009 Pearson Education Inc. 2.4 Why Is Carbon So Important To Life? The great variety of substances found in nature is therefore constructed from a limited pool of atoms. Organic molecules have a carbon skeleton and some hydrogen atoms. Much of the diversity of organic molecules is due to the presence of functional groups. Copyright © 2009 Pearson Education Inc. 2.4 Why Is Carbon So Important To Life? Copyright © 2009 Pearson Education Inc. 2.4 Why Is Carbon So Important To Life? PLAY Animation—Functional Groups Copyright © 2009 Pearson Education Inc. 2.5 How Are Biological Molecules Joined Together Or Broken Apart? Dehydration synthesis • The construction of large molecules yields water. • Small molecules are joined together to form large molecules. • During the joining of small molecules, water is released. • This water-releasing reaction is called dehydration synthesis. Copyright © 2009 Pearson Education Inc. 2.5 How Are Biological Molecules Joined Together Or Broken Apart? Dehydration synthesis dehydration synthesis + HO OH HO OH O HO H O OH H (a) Dehydration synthesis Fig. 2-12a Copyright © 2009 Pearson Education Inc. 2.5 How Are Biological Molecules Joined Together Or Broken Apart? Hydrolysis reactions • During the breakdown of large molecules, covalent bonds are broken, separating the subunits Copyright © 2009 Pearson Education Inc. 2.5 How Are Biological Molecules Joined Together Or Broken Apart? Hydrolysis hydrolysis + O HO H O OH HO OH HO OH H (b) Hydrolysis Fig. 2-12b Copyright © 2009 Pearson Education Inc. 2.5 How Are Biological Molecules Joined Together Or Broken Apart? PLAY Animation—Dehydration Synthesis and Hydrolysis Copyright © 2009 Pearson Education Inc. 2.6 What Are Carbohydrates? Carbohydrates are molecules composed of carbon, hydrogen, and oxygen in the ratio of 1:2:1. They can be small single sugar molecules or long chains of single sugar molecules strung together. Copyright © 2009 Pearson Education Inc. 2.6 What Are Carbohydrates? A simple sugar CH2OH H O H 6 H H 5 C H 4 C O O H 3 C 2 C O H H O H H (a) Glucose, linear form H 1 C C O O H H H H HO OH H H OH OH (b) Glucose, ring form Fig. 2-13 Copyright © 2009 Pearson Education Inc. 2.6 What Are Carbohydrates? Monosaccharide: a carbohydrate consisting of one sugar molecule Disaccharide: two sugars linked together Polysaccharide: three or more sugars linked together Copyright © 2009 Pearson Education Inc. 2.6 What Are Carbohydrates? Simple sugars, such as glucose, provide important energy sources for organisms. Sucrose, such as table sugar, is a disaccharide containing one glucose molecule attached to a fructose molecule. Copyright © 2009 Pearson Education Inc. 2.6 What Are Carbohydrates? Manufacture of a disaccharide glucose fructose CH2OH O H H HOCH2 CH2OH O O H H + HO OH H H OH OH sucrose HO H OH HO H dehydration CH2OH synthesis H H HO HOCH2 H OH H H OH O H OH O H HO CH2OH H O H H Fig. 2-14 Copyright © 2009 Pearson Education Inc. 2.6 What Are Carbohydrates? PLAY Animation—Carbohydrates Copyright © 2009 Pearson Education Inc. 2.6 What Are Carbohydrates? Some complex sugars, such as cellulose, provide support for cells or even the entire bodies of organisms. Complex sugars are made by the dehydration synthesis of simple sugars. Cellulose is the most abundant organic molecule on Earth because it provides support for plants in fields and forests. Cellulose is made of long chains of glucose subunits. Copyright © 2009 Pearson Education Inc. 2.6 What Are Carbohydrates? Cellulose structure wood is mostly cellulose plant cell with cell wall close-up of cell wall Hydrogen bonds cross-linking cellulose molecules CH2OH H O H O H OH OH O H H H CH2OH OH H H H H O OH CH2OH Copyright © 2009 Pearson Education Inc. OH OH H H O H OH O H H O H H H H O O H OH CH2OH individual cellulose molecules bundle of cellulose molecules cellulose fiber Fig. 2-15 2.6 What Are Carbohydrates? PLAY Animation—Carbohydrate Functions PLAY Animation—Structure Determines Function Copyright © 2009 Pearson Education Inc. 2.7 What Are Lipids? Molecular characteristics of lipids • Lipids are molecules with long regions composed almost entirely of carbon and hydrogen. • The nonpolar regions of carbon and hydrogen bonds make lipids hydrophobic and insoluble in water. Copyright © 2009 Pearson Education Inc. 2.7 What Are Lipids? Lipid classification • Group 1: Oils, fats, and waxes • Group 2: Phospholipids • Group 3: Steroids Copyright © 2009 Pearson Education Inc. 2.7 What Are Lipids? Group 1: Oils, fats, and waxes • Contain only carbon, hydrogen, and oxygen • Contain one or more fatty acid subunits—long chains of C and H with a carboxyl group (–COOH) • They usually do not have a ring structure. Copyright © 2009 Pearson Education Inc. 2.7 What Are Lipids? Group 1: Oils, fats, and waxes (continued) • Fats and oils form by dehydration synthesis from three fatty acid subunits and one molecule of glycerol. etc. CH2 CH2 CH2 H H C OH O CH HO C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH H C OH O HO C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 etc. + H C OH H glycerol O HO C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 etc. fatty acids Fig. 2-16 Copyright © 2009 Pearson Education Inc. 2.7 What Are Lipids? Group 1: Oils, fats, and waxes (continued) • Fats and oils formed by dehydration synthesis are called triglycerides. • Triglycerides are used for long-term energy storage in both plants and animals. etc. CH2 CH2 CH2 H O CH H C O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH + O H O O H C O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 etc. + H O H C O C CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 etc. H + H triglyceride H H O H 3 water molecules Fig. 2-16 Copyright © 2009 Pearson Education Inc. 2.7 What Are Lipids? PLAY Animation—Lipids Copyright © 2009 Pearson Education Inc. 2.7 What Are Lipids? Group 1: Oils, fats, and waxes (continued) • Characteristics of fats • Fats are solid at room temperature. • Fats have all carbons joined by single covalent bonds. • The remaining bond positions on the carbons are occupied by hydrogen atoms. Copyright © 2009 Pearson Education Inc. 2.7 What Are Lipids? Group 1: Oils, fats, and waxes (continued) • Fatty acids of fats are said to be saturated and are straight molecules that can be stacked. (a) Beef fat (saturated) Fig. 2-18a Copyright © 2009 Pearson Education Inc. 2.7 What Are Lipids? Group 1: Oils, fats, and waxes (continued) • Characteristics of oils • Oils are liquid at room temperature. • Some of the carbons in fatty acids have double covalent bonds. • There are fewer attached hydrogen atoms, and the fatty acid is said to be unsaturated. Copyright © 2009 Pearson Education Inc. 2.7 What Are Lipids? Group 1: Oils, fats, and waxes (continued) • Unsaturated fatty acids have bends and kinks in fatty acid chains and can’t be stacked. (b) Peanut oil (unsaturated) Fig. 2-18b Copyright © 2009 Pearson Education Inc. 2.7 What Are Lipids? Group 1: Oils, fats, and waxes (continued) • Characteristics of waxes • Waxes are solid at room temperature. • Waxes are highly saturated. • Waxes are not a food source. • Waxes form waterproof coatings over plant leaves and stems. Copyright © 2009 Pearson Education Inc. 2.7 What Are Lipids? Group 1: Oils, fats, and waxes (continued) • Bees use waxes to store food and honey. Fig. 2-17b Copyright © 2009 Pearson Education Inc. 2.7 What Are Lipids? PLAY Animation—Lipid Function Copyright © 2009 Pearson Education Inc. 2.7 What Are Lipids? Group 2: Phospholipids • Phospholipids have water-soluble heads and water-insoluble tails. • They are found in cell membranes in a double layer. • They are like oils except one fatty acid is replaced by a phosphate group attached to glycerol. Copyright © 2009 Pearson Education Inc. 2.7 What Are Lipids? Group 2: Phospholipids (continued) • The phosphate end of the molecule is water soluble; the fatty acid end of the molecule is water insoluble. CH3 O– H3C - N+- CH2 - CH2 -O-P- O -CH2 O CH3 O HC-O-C- CH2 -CH2 - CH2 - CH2 - CH2 - CH2 - CH2 -CH O CH CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3 H2C-O-C- CH2 -CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 - CH2 -CH3 polar head glycerol (hydrophilic) fatty acid tails (hydrophobic) Fig. 2-19 Copyright © 2009 Pearson Education Inc. 2.7 What Are Lipids? Group 3: Steroids • Steroids contain four carbon rings fused together. • Various functional groups protrude from the basic steroid “skeleton”. • Cholesterol is a steroid found in cell membranes. Copyright © 2009 Pearson Education Inc. 2.7 What Are Lipids? Group 3: Steroids • Testosterone and estrogen are male and female reproductive hormones, respectively, and are steroids. OH CH3 CH3 HC CH3 CH2 CH2 HO (b) Estrogen CH2 HC CH3 CH3 OH CH3 CH3 CH3 HO O (a) Cholesterol (c) Testosterone Fig. 2-20 Copyright © 2009 Pearson Education Inc. 2.8 What Are Proteins? Functions of proteins • Proteins act as enzymes to catalyze many biochemical reactions. • They can act as energy stores. • They are involved in carrying oxygen around the body. • They are involved in muscle movement. Copyright © 2009 Pearson Education Inc. 2.8 What Are Proteins? Some proteins are structural and provide support in hair, horns, spider webs, etc. Fig. 2-21 Copyright © 2009 Pearson Education Inc. 2.8 What Are Proteins? Proteins are formed from chains of amino acids. • All amino acids have the same basic structure: • A central carbon • An attached amino group • An attached carboxyl group • An attached variable side group Copyright © 2009 Pearson Education Inc. 2.8 What Are Proteins? Amino acid structure variable group R H amino group O N H C carboxylic acid group C H O H hydrogen Fig. 2-22 Copyright © 2009 Pearson Education Inc. 2.8 What Are Proteins? Amino acids join to form chains by dehydration synthesis. • Proteins are formed by dehydration reactions between individual amino acids. • The –NH2 group of one amino acid is joined to the –COOH group of another, with the release of H2O and the formation of a new peptide (two or more amino acids). Copyright © 2009 Pearson Education Inc. 2.8 What Are Proteins? More and more individual amino acids are added to the peptide until a polypeptide (protein) is formed. amino acid R H N H amino group C H amino acid O C N + O R H H H carboxylic amino acid group group C H water peptide O H C N O H H R O H R C C N C H H O C + O H O H H peptide bond Fig. 2-23 Copyright © 2009 Pearson Education Inc. 2.8 What Are Proteins? PLAY Animation—Proteins Copyright © 2009 Pearson Education Inc. 2.8 What Are Proteins? Three-dimensional shapes give proteins their functions. • Long chains of amino acids fold into threedimensional shapes in cells, which allows the protein to perform its specific functions. • When a protein is denatured, its shape has been disrupted and it may not be able to perform its function. Copyright © 2009 Pearson Education Inc. 2.8 What Are Proteins? H C H O C C N N O C C lys helix pro O C N O C N O C H N val O C C lys N H N O C H C O C H hydrogen bond (b) Secondary structure: Folding usually maintained by hydrogen bonds C ala H his H O C C gly N N H lys C lys N H O C O C val C N H leu H C R (a) Primary structure: The sequence of amino acids linked by peptide bonds (c) Tertiary structure: Folding results from bonds with surrounding water molecules and between amino acids (d) Quaternary structure: Individual polypeptides are linked to one another Fig. 2-24 Copyright © 2009 Pearson Education Inc. 2.8 What Are Proteins? PLAY Animation—Protein Function Copyright © 2009 Pearson Education Inc. 2.9 What Are Nucleic Acids? Structure of nucleic acids • Nucleic acids are long chains of similar, but not identical, subunits called nucleotides. Copyright © 2009 Pearson Education Inc. 2.9 What Are Nucleic Acids? Structure of nucleic acids (continued) • All nucleotides have three parts. • A five-carbon sugar (ribose or deoxyribose) • A phosphate group • A nitrogen-containing molecule called a base Copyright © 2009 Pearson Education Inc. 2.9 What Are Nucleic Acids? Deoxyribose nucleotide base NH2 phosphate N C C N OH HO P HC O CH2 O H N C N CH O sugar H H OH H H Fig. 2-25 Copyright © 2009 Pearson Education Inc. 2.9 What Are Nucleic Acids? Types of nucleotides • Those that contain the sugar ribose. • Those that contain the sugar deoxyribose. • Nucleotides string together in long chains as nucleic acids with the phosphate group of one nucleotide bonded to the sugar group of another. Copyright © 2009 Pearson Education Inc. 2.9 What Are Nucleic Acids? Nucleotide chain base sugar phosphate Fig. 2-26 Copyright © 2009 Pearson Education Inc. 2.9 What Are Nucleic Acids? DNA and RNA, the molecules of heredity, are nucleic acids. • There are two types of nucleic acids. • Deoxyribonucleic acid (DNA): contains the genetic code of cell • Ribonucleic acid (RNA): is used in the synthesis of proteins Copyright © 2009 Pearson Education Inc. 2.9 What Are Nucleic Acids? PLAY Animation—Nucleic Acids PLAY Animation—Nucleic Acids Copyright © 2009 Pearson Education Inc. 2.9 What Are Nucleic Acids? Other nucleotides perform other functions. • Adenosine monophosphate: acts as a messenger in the cell, carrying information to other molecules • Adenosine triphosphate: carries energy from place to place in the cell Copyright © 2009 Pearson Education Inc.