1. Chapter 3: Chemistry of Life

2. Section 1: Matter and Substances Preview Atoms Chemical Bonds Polarity Summary

3. Atoms Every living and nonliving thing is made of matter. Matter is anything that has mass and takes up space. All matter is made of very small particles called atoms. An atom is the smallest unit of matter that cannot be broken down by chemical means. An atom has a positively charged core surrounded by a negatively charged region.

4. Atoms, continued The nucleus of an atom is made up of positively charged protons and uncharged neutrons. Negatively charged electrons have very little mass and move around the nucleus in a large region called the electron cloud.

5. Elements An element is a substance made up of atoms that have the same number of protons. For example, each atom of the element carbon has six protons. –The atomic number is based on the number of protons Atoms of an element may have different numbers of neutrons. These atoms are called isotopes of elements.

6. Most common elements in living things are carbon, hydrogen, nitrogen, and oxygen. These four elements constitute about 95% of your body weight.

7. Chemical Bonds The electron cloud of an atom may have levels. Electrons in the outermost level, or shell, are called valence electrons. Atoms tend to combine with each other such that eight electrons will be in the valence shell. When atoms combine, a force called a chemical bond holds them together.

8. Chemical Bonds, continued Chemical bonds form between groups of atoms because most atoms become stable when they have eight electrons in the valence shell. When atoms of different elements combine, a compound forms. A compound is a substance made of the bonded atoms of two or more elements.

9. Chemical Bonds, continued Covalent Bonding One way that atoms bond is by sharing valence electrons to form a covalent bond. A molecule is a group of atoms held together by covalent bonds. A water molecule, H2O, forms when an oxygen atom forms covalent bonds with two hydrogen atoms.

10. Visual Concept: Covalent Bonding

11. Chemical Bonds, continued Ionic Bonding Atoms can achieve a stable valence level by losing or gaining electrons, resulting in a positive or negative charge. An ion is an atom or group of atoms that has an electric charge because it has gained or lost electrons. The attractive force between oppositely charged ions is an ionic bond.

12. Visual Concept: Ion

13. Ionic Bonding in Salt Click to animate the image.

14. Polarity In some covalent bonds, the shared electrons are attracted more strongly to one atom than to the other. As a result, one end of the molecule has a partial negative charge, while the opposite end has a partial positive charge. Molecules with partial charges on opposite ends are said to be polar.

15. Polarity, continued Solubility The partially charged ends of polar molecules attract opposite charges. Because of this behavior, polar molecules can dissolve other polar molecules and ionic compounds. For example, water can dissolve sugar and salt. Nonpolar substances, such as oil, grease, and wax, do not dissolve well in water.

16. Ionic Compounds in Water

17. Polarity, continued Hydrogen Bonds When bonded to an oxygen, nitrogen, or fluorine atom, a hydrogen atom has a partial charge nearly as great as a proton’s charge. It attracts the negative pole of other nearby molecules. This attraction, called a hydrogen bond, is stronger than attractions between other molecules, but not as strong as covalent bonds. Hydrogen bonding plays an important role in many of the molecules that make up living things.

18. Hydrogen Bonding

19. Summary All matter is made up of atoms. An atom has a positively charged nucleus surrounded by a negatively charged electron cloud. Chemical bonds form between groups of atoms because most atoms became stable when they have eight electrons in the valence shell. Polar attractions and hydrogen bonds are forces that play an important role in many of the molecules that make up living things.

20. Concept Check What makes up matter? Why do atoms form bonds? What are some important interactions between substances in living things?

21. Test Prep

22. A. the size of the electrons B. the shape of the nucleus C. the number of neutrons in each atom D. the electrons in the atoms of the elements 1. The way in which elements bond to form compounds depends on which of the following?

23. A. ionic B. nuclear C. covalent D. hydrogen 2. In what type of bond are electrons shared?

24. A. ionic B. nuclear C. covalent D. hydrogen 3. What weak bond holds together the two strands of nucleotides in a DNA molecule?

25. Section 2: Water and Solutions Preview Properties of Water Solutions Summary

26. Properties of Water Water has many unique properties that make it an important substance for life. Most of the unique properties of water result because water molecules form hydrogen bonds with each other. When water freezes, the crystal structure formed due to hydrogen bonding makes ice less dense than liquid water.

27. Properties of Water, continued Water can absorb a large amount of heat without changing temperature. This property can help organisms maintain a constant internal temperature. The attraction of particles of the same substance, such as water, is called cohesion. Cohesion keep water from evaporating easily; thus, water is a liquid at ordinary temperatures. Water molecules also stick to other polar molecules. This attraction between particles of different substances is called adhesion.

28. Visual Concept: Comparing Cohesion and Adhesion

29. Solutions A solution is a mixture in which ions or molecules of one or more substances are evenly distributed in another substance. Many substances are transported throughout living things as solutions of water. Dissolved substances can move more easily within and between cells. Water dissolves many ionic and polar substances but does not dissolve nonpolar substances.

30. Solutions, continued Acids and Bases Some water molecules break apart to form hydronium and hydroxide ions. In pure water, hydronium and hydroxide ions are present in equal numbers. Acids and bases are compounds that change the balance of these ions.

31. Solutions

32. Solutions, continued Acids and Bases Acids are compounds that form extra hydronium ions when dissolved in water. Bases are compounds that form extra hydroxide ions when dissolved in water. When acids and bases are mixed, the extra hydronium and hydroxide ions react to form water.

33. Visual Concept: Acids

34. Visual Concept: Bases

35. Solutions, continued pH and Buffers pH is a measure of how acidic or basic a solution is. Each one-point increase in pH represents a 10-fold decrease in hydronium ion concentration. Pure water has a pH of 7. Acidic solutions have a pH below 7, and basic solutions have a pH above 7.

36. Visual Concept: pH

37. Solutions, continued pH and Buffers The pH of solutions in living things must be stable. For a stable pH to be maintained, the solutions in living things contain buffers. A buffer is a substance that reacts to prevent pH changes in a solution.

38. Summary The hydrogen bonding between water molecules explains many of the unique properties that make water an important substance for life. Acids and bases change the concentration of hydronium ions in aqueous solutions. The pH of solutions in living things must be stable.

39. Concept Check What makes water a unique substance? How does the presence of substances dissolved in water affect the properties of water?

40. Test Prep

41. A. The substance is a gas. B. The substance is a base. C. The substance is an acid. D. The substance is a carbohydrate. 4. When an unknown substance is dissolved in water, hydronium ions form. What can you conclude about the substance?

42. Section 3: Carbon Compounds Preview Building Blocks of Cells Carbohydrates Lipids Proteins Nucleic Acids Summary

43. Building Blocks of Cells The parts of a cell are made up of large, complex molecules, often called biomolecules. Large, complex biomolecules are built from a few smaller, simpler, repeating units arranged in an extremely precise way. The basic unit of most biomolecules contain atoms of carbon. Carbon atoms can form covalent bonds with as many as four other atoms.

44. Carbon Bonding

45. Condensation and Hydrolysis 1. Small molecules can combine to form large ones because of special proteins called enzymes that can speed up a chemical reaction.

46. 2. In condensation, one molecule is stripped of its H +, another is stripped of its OH –. The two molecule fragments join to form a new compound and the H + and OH – form water.

47. 3. Hydrolysis is the reverse: one molecule is split by the addition of H + and OH – (from water) to the components.

48. Carbohydrates Carbohydrates are molecules made of sugars. A sugar contains carbon, hydrogen, and oxygen in a ratio of 1:2:1. Glucose is a common sugar found in grape juice.

49. Carbohydrates, continued Glucose is a monosaccharide, or “single sugar.” Two sugars can be linked to make a disaccharide. Many sugars can be linked to make a polysaccharide. Monosaccharides and disaccharides are considered simple carbohydrates. Polysaccharides are considered complex carbohydrates.

50. Monosaccharide

51. Disaccharides

52. Polysaccharide

53. Visual Concept: Carbohydrates

54. Carbohydrates, continued Cells use carbohydrates for sources of energy, structural materials, and cellular identification. Carbohydrates are a major source of energy for many organisms, including humans.

55. Carbohydrates, continued Chitin and cellulose are complex carbohydrates that provide support. Chitin is found in the shells of insects and the cell walls of mushrooms. Cellulose is found in the cell walls of plants. In a complex organism, cells recognize neighboring cells by the short, branched chains of varying sugar units on their outer surface.

56. Lipids Lipids are another class of biomolecules, which includes fats, phospholipids, steroids, and waxes. Lipids consist of chains of carbon atoms bonded to each other and to hydrogen atoms. This structure makes lipids repel water. The main functions of lipids include storing energy and controlling water molecules.

57. Lipids, continued The main purpose of fats is to store energy. Fats can store energy even more efficiently than carbohydrates. The cell’s boundary is made of phospholipids. The structure of cell membranes depends on how this molecule interacts with water. Waxes, found on the surfaces of plants and aquatic bird feathers, help prevent evaporation of water from the cells of the organism.

58. Visual Concept: Types of Lipids

59. Proteins Proteins are chains of amino acids that twist and fold into certain shapes that determine what the proteins do. There are many types of proteins that perform many types of functions. Proteins may be involved in structure, support, movement, communication, transportation, and carrying out chemical reactions.

60. Visual Concept: Proteins

61. Proteins, continued Amino Acids A protein is a molecule made up of amino acids, building blocks that link to form proteins. Every amino acid has an amino group and a carboxyl group. Units of amino acids can form links called peptide bonds. The side group gives an amino acid its unique properties. Twenty different amino acids are found in proteins.

62. Visual Concept: Amino Acid

63. Proteins, continued Levels of Structure For each type of protein, amino acids are arranged in a specific order, the protein’s primary structure. The interactions of the various side groups may form coils and folds, the protein’s secondary structure. The overall shape of a single chain of amino acids is the protein’s tertiary structure. The quaternary structure is the overall shape that results from combining the chains to form proteins.

65. Nucleic Acids A nucleic acid is a long chain of nucleotide units. A nucleotide is a molecule made up of three parts: a sugar, a base, and a phosphate group. Nucleotides of deoxyribonucleic acid, or DNA, contain the sugar deoxyribose. Nucleotides of ribonucleic acid, or RNA, contain the sugar ribose.

66. Constituents of nucleic acids

67. Visual Concept: Nucleic Acid

68. Nucleic Acids, continued Hereditary Information DNA molecules act as “instructions” for the processes of an organism’s life. DNA consists of two strands of nucleotides that spiral around each other. RNA also interacts with DNA to help decode the information. Nucleic acids store and transmit hereditary information.

69. Nucleic Acids, continued Energy Carriers Some single nucleotides have other important roles. Adenosine triphosphate, or ATP, is a nucleotide that has three phosphate groups and supplies energy to cells. Energy is released in the reaction that breaks off the third phosphate group. Other single nucleotides transfer electrons or hydrogen atoms for other life processes.

70. Summary Large, complex biomolecules are built from a few smaller, simpler, repeating units arranged in an extremely precise way. Cells use carbohydrates for sources of energy, structural materials, and cellular identification. The main functions of lipids include storing energy and controlling water movement

71. Summary, continued Proteins are chains of amino acids that twist and fold into shapes that determine what the protein does. Nucleic acids store and transmit hereditary information.

72. Concept Check What are the chemicals of life made from? What is the role of carbohydrates in cells? What do lipids do? What determines the function of proteins? What do nucleic acids do?

73. Test Prep

74. A. ionic bond B. peptide bond C. covalent bond D. hydrogen bond The diagram shows a type of biomolecule. Use the diagram to answer the following question(s). 5. A bond can form between Group 1 of this type of molecule and Group 3 of another type of this molecule. What is this bond called?

75. A. lipids B. proteins C. nucleic acids D. carbohydrates 6. Carboxypeptidase is an enzyme that catalyzes reactions in the small intestine. The products of these reactions are amino acids. What are the substrates of carboxypeptidase?

76. Section 4: Energy and Metabolism Preview Changing Matter Chemical Reactions Biological Reactions Summary

77. Changing Matter Living things are made of matter, which consists of a substance with a form. Changes constantly occur in living things. A physical change occurs when only the form or shape of the matter changes. A chemical change occurs when a substance changes into a different substance.

78. Changing Matter, continued Matter is neither created nor destroyed in any change. This observation is called the law of conservation of mass. The ability to move or change matter is called energy. Energy exists in many forms and can be converted from one form to another. Every change in matter requires a change in energy.

79. Visual Concept: Energy

80. Changing Matter, continued Energy may change from one form to another, but the total amount of energy does not change. This observation is called the law of conservation of energy. The total amount of usable energy decreases because some energy is given off to the surroundings as heat. Living things use different chemical reactions to get the energy needed for life processes.

81. Chemical Reactions Changing a substance requires a chemical reaction. During this process, bonds between atoms are broken, and new ones are formed. A reactant is a substance that is changed in a chemical reaction A product is a new substance that is formed. Sometimes products can reform reactants.

82. Chemical Reactions, continued Activation Energy Chemical reactions can only occur under the right conditions. To form new bonds, the particles must collide fast enough to overcome the repulsion between their negatively charged electron clouds. The activation energy of a reaction is the minimum kinetic energy required to start a chemical reaction.

83. Visual Concept: Activation Energy and Chemical Reactions

84. Chemical Reactions, continued Alignment Even if enough energy is available, the product still may not form. When the reactant particles, the correct atoms must be brought close together in the proper orientation. Chemical reactions can only occur when the activation energy is available and the correct atoms are aligned.

85. Reaction Conditions

86. Biological Reactions In living things, chemical reactions occur between large, complex biomolecules. Many of these reactions require large activation energies. Many of these reactions would not occur quickly enough to sustain life without the help of enzymes.

87. Biological Reactions, continued Enzymes An enzyme is a molecule that increases the speed of biochemical reactions. Enzymes hold molecules close together and in the correct orientation. An enzyme lowers the activation energy of a reaction. By assisting in necessary biochemical reactions, enzymes help organisms maintain homeostasis.

88. Effect of Enzyme on Activation Energy

89. Biological Reactions, continued Enzymes Each enzyme has an active site, the region where the reaction takes place. The shape of the active site determines which reactants, or substrates, will bind to it. Each different enzyme acts only on specific substrates. Binding of the substrates causes the enzyme’s shape to change. This change causes some bonds in the substrates to break and new bonds to form.

90. Enzyme Action Click to animate the image.

91. Biological Reactions, continued Enzymes Many enzymes are proteins. Changes in temperature and pH can change a protein’s shape. If an enzyme changes shape, it won’t work well. Most enzymes need a certain range of temperatures and pH.

92. Biological Reactions, continued Metabolism Cells get most of the energy needed for metabolism by breaking down food molecules. The release of energy from food molecules occurs in a series of reactions using many enzymes to capture energy in the form of ATP molecules. The enzymes reduce the activation energy so much that only a little energy is needed to start the reactions. In this process, very little energy is lost as heat.

93. Summary Living things use different chemical reactions to get the energy needed for life processes. An activation energy is needed to start a chemical reaction. The reactants must also be aligned to form the product. By assisting in necessary biochemical reactions, enzymes help organisms maintain homeostasis.

94. Concept Check Where do living things get energy? How do chemical reactions occur? Why are enzymes important to living things?

95. Test Prep

96. A. chemical energy B. electrical energy C. activation energy D. mechanical energy The graph shows the energy in a catalyzed chemical reaction as the reaction progresses. Use the graph to answer the following question(s). 7. The amount of energy needed for this chemical reaction to begin is shown by the line rising from the reactants. What is this energy called?

97. A. larger than what is shown B. the same as what is shown C. smaller than what is shown D. very similar to what is shown The graph shows the energy in a catalyzed chemical reaction as the reaction progresses. Use the graph to answer the following question(s). 8. Suppose that this reaction needs a catalyst to proceed. In the absence of a catalyst, the activation energy would be which of the following?