Chapter Opener 2 © 2013 Pearson Education, Inc.

Figure 2.1 Two models of the structure of an atom. Nucleus Nucleus Helium atom Helium atom 2 protons (p+) 2 protons (p+) 2 neutrons (n0) 2 neutrons (n0) 2 electrons (e–) 2 electrons (e–) Planetary model Orbital model Proton Neutron Electron Electron cloud © 2013 Pearson Education, Inc.

Figure 2.1a Two models of the structure of an atom. Nucleus Helium atom 2 protons (p+) 2 neutrons (n0) 2 electrons (e–) Planetary model Proton Neutron Electron Electron cloud © 2013 Pearson Education, Inc.

Figure 2.1b Two models of the structure of an atom. Nucleus Helium atom 2 protons (p+) 2 neutrons (n0) 2 electrons (e–) Orbital model Proton Neutron Electron Electron cloud © 2013 Pearson Education, Inc.

Table 2.1 Common Elements Composing the Human Body (1 of 3) © 2013 Pearson Education, Inc.

Table 2.1 Common Elements Composing the Human Body (2 of 3) © 2013 Pearson Education, Inc.

Table 2.1 Common Elements Composing the Human Body (3 of 3) © 2013 Pearson Education, Inc.

Figure 2.2 Atomic structure of the three smallest atoms. Proton Neutron Electron Hydrogen (H) (1p+; 0n0; 1e–) Helium (He) (2p+; 2n0; 2e–) Lithium (Li) (3p+; 4n0; 3e–) © 2013 Pearson Education, Inc.

Figure 2.3 Isotopes of hydrogen. Proton Neutron Electron Hydrogen (1H) (1p+; 0n0; 1e–) Deuterium (2H) (1p+; 1n0; 1e–) Tritium (3H) (1p+; 2n0; 1e–) © 2013 Pearson Education, Inc.

Figure 2.4 The three basic types of mixtures. Solution Colloid Suspension Solute particles are very tiny, do not settle out or scatter light. Solute particles are larger than in a solution and scatter light; do not settle out. Solute particles are very large, settle out, and may scatter light. Solute particles Solute particles Solute particles Example Example Example Mineral water Jello Blood Plasma Settled red blood cells Unsettled Settled © 2013 Pearson Education, Inc.

Figure 2.5 Chemically inert and reactive elements. Chemically inert elements Outermost energy level (valence shell) complete 8e 2e 2e Helium (He) (2p+; 2n0; 2e–) Neon (Ne) (10p+; 10n0; 10e–) Chemically reactive elements Outermost energy level (valence shell) incomplete 4e 1e 2e Hydrogen (H) (1p+; 0n0; 1e–) Carbon (C) (6p+; 6n0; 6e–) 1e 6e 8e 2e 2e Oxygen (O) (8p+; 8n0; 8e–) Sodium (Na) (11p+; 12n0; 11e–) © 2013 Pearson Education, Inc.

Figure 2.5a Chemically inert and reactive elements. Chemically inert elements Outermost energy level (valence shell) complete 8e 2e 2e Helium (He) (2p+; 2n0; 2e–) Neon (Ne) (10p+; 10n0; 10e–) © 2013 Pearson Education, Inc.

Figure 2.5b Chemically inert and reactive elements. Chemically reactive elements Outermost energy level (valence shell) incomplete 4e 1e 2e Hydrogen (H) (1p+; 0n0; 1e–) Carbon (C) (6p+; 6n0; 6e–) 1e 6e 8e 2e 2e Oxygen (O) (8p+; 8n0; 8e–) Sodium (Na) (11p+; 12n0; 11e–) © 2013 Pearson Education, Inc.

Figure 2.6 Formation of an ionic bond. + — Sodium atom (Na) (11p+; 12n0; 11e–) Chlorine atom (Cl) (17p+; 18n0; 17e–) Sodium ion (Na+) Chloride ion (Cl–) Sodium chloride (NaCl) Sodium gains stability by losing one electron, and chlorine becomes stable by gaining one electron. After electron transfer, the oppositely charged ions formed attract each other. Cl– Na+ Large numbers of Na+ and Cl– ions associate to form salt (NaCl) crystals. © 2013 Pearson Education, Inc.

Figure 2.6a Formation of an ionic bond. Sodium atom (Na) (11p+; 12n0; 11e–) Chlorine atom (Cl) (17p+; 18n0; 17e–) Sodium gains stability by losing one electron, and chlorine becomes stable by gaining one electron. © 2013 Pearson Education, Inc.

Figure 2.6b Formation of an ionic bond. + — Sodium ion (Na+) Chloride ion (Cl–) Sodium chloride (NaCl) After electron transfer, the oppositely charged ions formed attract each other. © 2013 Pearson Education, Inc.

Figure 2.6c Formation of an ionic bond. Cl– Na+ Large numbers of Na+ and Cl– ions associate to form salt (NaCl) crystals. © 2013 Pearson Education, Inc.

Figure 2.7 Formation of covalent bonds. Reacting atoms Resulting molecules + or Structural formula shows single bonds. Hydrogen atoms Carbon atom Molecule of methane gas (CH4) Formation of four single covalent bonds: Carbon shares four electron pairs with four hydrogen atoms. + or Structural formula shows double bond. Oxygen atom Oxygen atom Molecule of oxygen gas (O2) Formation of a double covalent bond: Two oxygen atoms share two electron pairs. + or Structural formula shows triple bond. Nitrogen atom Nitrogen atom Molecule of nitrogen gas (N2) Formation of a triple covalent bond: Two nitrogen atoms share three electron pairs. © 2013 Pearson Education, Inc.

Figure 2.7a Formation of covalent bonds. Reacting atoms Resulting molecules + or Structural formula shows single bonds. Hydrogen atoms Carbon atom Molecule of methane gas (CH4) Formation of four single covalent bonds: Carbon shares four electron pairs with four hydrogen atoms. © 2013 Pearson Education, Inc.

Figure 2.7b Formation of covalent bonds. Reacting atoms Resulting molecules + or Structural formula shows double bond. Oxygen atom Oxygen atom Molecule of oxygen gas (O2) Formation of a double covalent bond: Two oxygen atoms share two electron pairs. © 2013 Pearson Education, Inc.

Figure 2.7c Formation of covalent bonds. Reacting atoms Resulting molecules + or Structural formula shows triple bond. Nitrogen atom Nitrogen atom Molecule of nitrogen gas (N2) Formation of a triple covalent bond: Two nitrogen atoms share three electron pairs. © 2013 Pearson Education, Inc.

Carbon dioxide (CO2) molecules are Figure 2.8 Carbon dioxide and water molecules have different shapes, as illustrated by molecular models. Carbon dioxide (CO2) molecules are linear and symmetrical. They are nonpolar. – +  + V-shaped water (H2O) molecules have two poles of charge—a slightly more negative oxygen end (–) and a slightly more positive hydrogen end (+). © 2013 Pearson Education, Inc.

Carbon dioxide (CO2) molecules are Figure 2.8a Carbon dioxide and water molecules have different shapes, as illustrated by molecular models. Carbon dioxide (CO2) molecules are linear and symmetrical. They are nonpolar. © 2013 Pearson Education, Inc.

V-shaped water (H2O) molecules have two Figure 2.8b Carbon dioxide and water molecules have different shapes, as illustrated by molecular models. δ– δ+ δ+ V-shaped water (H2O) molecules have two poles of charge—a slightly more negative oxygen end (δ–) and a slightly more positive hydrogen end (δ+). © 2013 Pearson Education, Inc.

Ionic bond Polar covalent bond Nonpolar covalent bond Complete Figure 2.9 Ionic, polar covalent, and nonpolar covalent bonds compared along a continuum. Ionic bond Polar covalent bond Nonpolar covalent bond Complete transfer of electrons Unequal sharing of electrons Equal sharing of electrons Separate ions (charged particies) form Slight negative charge (δ–) at one end of molecule, slight positive charge (δ) at other end Charge balanced among atoms δ– δ+ δ+ Sodium chloride Water Carbon dioxide © 2013 Pearson Education, Inc.

Figure 2.10 Hydrogen bonding between polar water molecules. δ+ δ− Hydrogen bond (indicated by dotted line) δ+ δ+ δ− δ− δ− δ+ δ+ δ+ δ− The slightly positive ends (δ) of the water molecules become aligned with the slightly negative ends (δ−) of other water molecules. A water strider can walk on a pond because of the high surface tension of water, a result of the combined strength of its hydrogen bonds. © 2013 Pearson Education, Inc.

Figure 2.10a Hydrogen bonding between polar water molecules. δ+ δ− Hydrogen bond (indicated by dotted line) δ+ δ+ δ− δ− δ− δ+ δ+ δ+ δ− The slightly positive ends (δ) of the water molecules become aligned with the slightly negative ends (δ−) of other water molecules. © 2013 Pearson Education, Inc.

Figure 2.10b Hydrogen bonding between polar water molecules. A water strider can walk on a pond because of the high surface tension of water, a result of the combined strength of its hydrogen bonds. © 2013 Pearson Education, Inc.

Figure 2.11 Patterns of chemical reactions. Synthesis reactions Decomposition reactions Exchange reactions Smaller particles are bonded together to form larger, more complex molecules. Bonds are broken in larger molecules, resulting in smaller, less complex molecules. Bonds are both made and broken (also called displacement reactions). Example Example Example Amino acids are joined together to form a protein molecule. Glycogen is broken down to release glucose units. ATP transfers its terminal phosphate group to glucose to form glucose- phosphate. Amino acid molecules Glycogen Adenosine triphosphate (ATP) Glucose Protein molecule Glucose molecules Adenosine diphosphate (ADP) Glucose- phosphate © 2013 Pearson Education, Inc.

Figure 2.11a Patterns of chemical reactions. Synthesis reactions Smaller particles are bonded together to form larger, more complex molecules. Example Amino acids are joined together to form a protein molecule. Amino acid molecules Protein molecule © 2013 Pearson Education, Inc.

Figure 2.11b Patterns of chemical reactions. Decomposition reactions Bonds are broken in larger molecules, resulting in smaller, less complex molecules. Example Glycogen is broken down to release glucose units. Glycogen Glucose molecules © 2013 Pearson Education, Inc.

Figure 2.11c Patterns of chemical reactions. Exchange reactions Bonds are both made and broken (also called displacement reactions). Example ATP transfers its terminal phosphate group to glucose to form glucose- phosphate. + Adenosine triphosphate (ATP) Glucose + Adenosine diphosphate (ADP) Glucose- phosphate © 2013 Pearson Education, Inc.

Figure 2.12 Dissociation of salt in water. δ+ δ– δ+ Water molecule Salt crystal Ions in solution © 2013 Pearson Education, Inc.

Figure 2.13 The pH scale and pH values of representative substances. Concentration (moles/liter) [OH−] [H+] pH Examples 100 10−14 14 1M Sodium hydroxide (pH=14) 10−1 10−13 13 Oven cleaner, lye (pH=13.5) 10−2 10−12 12 10−3 10−11 11 Household ammonia (pH=10.5–11.5) Increasingly basic 10−4 10−10 10 Household bleach (pH=9.5) 10−5 10−9 9 Egg white (pH=8) 10−6 10−8 8 Blood (pH=7.4) 10−7 10−7 7 Neutral Milk (pH=6.3–6.6) 10−8 10−6 6 10−9 10−5 5 Black coffee (pH=5) 10−10 10−4 4 Increasingly acidic Wine (pH=2.5–3.5) 10−11 10−3 3 10−12 10−2 2 Lemon juice; gastric juice (pH=2) 10−13 10−1 1 1M Hydrochloric acid (pH=0) 10−14 100 © 2013 Pearson Education, Inc.

Figure 2.14 Dehydration synthesis and hydrolysis. Monomers are joined by removal of OH from one monomer and removal of H from the other at the site of bond formation. + Monomer 1 Monomer 2 Monomers linked by covalent bond Hydrolysis Monomers are released by the addition of a water molecule, adding OH to one monomer and H to the other. Monomer 1 + Monomer 2 Monomers linked by covalent bond Example reactions Dehydration synthesis of sucrose and its breakdown by hydrolysis Water is released + Water is consumed Glucose Fructose Sucrose © 2013 Pearson Education, Inc.

Figure 2.14a Dehydration synthesis and hydrolysis. Monomers are joined by removal of OH from one monomer and removal of H from the other at the site of bond formation. Monomer 1 + Monomer 2 Monomers linked by covalent bond © 2013 Pearson Education, Inc.

Figure 2.14b Dehydration synthesis and hydrolysis. Monomers are released by the addition of a water molecule, adding OH to one monomer and H to the other. Monomer 1 + Monomer 2 Monomers linked by covalent bond © 2013 Pearson Education, Inc.

Figure 2.14c Dehydration synthesis and hydrolysis. Example reactions Dehydration synthesis of sucrose and its breakdown by hydrolysis Water is released + Water is consumed Glucose Fructose Sucrose © 2013 Pearson Education, Inc.

Figure 2.15 Carbohydrate molecules important to the body. Monosaccharides Monomers of carbohydrates Example Hexose sugars (the hexoses shown here are isomers) Example Pentose sugars Glucose Fructose Galactose Deoxyribose Ribose Disaccharides Consist of two linked monosaccharides Example Sucrose, maltose, and lactose (these disaccharides are isomers) Glucose Fructose Glucose Glucose Galactose Glucose Sucrose Maltose Lactose Polysaccharides Long chains (polymers) of linked monosaccharides Example This polysaccharide is a simplified representation of glycogen, a polysaccharide formed from glucose units. Glycogen © 2013 Pearson Education, Inc.

Figure 2.15a Carbohydrate molecules important to the body. Monosaccharides Monomers of carbohydrates Example Hexose sugars (the hexoses shown here are isomers) Example Pentose sugars Glucose Fructose Galactose Deoxyribose Ribose © 2013 Pearson Education, Inc.

Figure 2.15b Carbohydrate molecules important to the body. Disaccharides Consist of two linked monosaccharides Example Sucrose, maltose, and lactose (these disaccharides are isomers) Glucose Fructose Glucose Glucose Galactose Glucose Sucrose Maltose Lactose © 2013 Pearson Education, Inc.

Figure 2.15c Carbohydrate molecules important to the body. Polysaccharides Long chains (polymers) of linked monosaccharides Example This polysaccharide is a simplified representation of glycogen, a polysaccharide formed from glucose units. Glycogen © 2013 Pearson Education, Inc.

Phosphorus-containing Figure 2.16 Lipids. Triglyceride formation Three fatty acid chains are bound to glycerol by dehydration synthesis. + + Glycerol 3 fatty acid chains Triglyceride, or neutral fat 3 water molecules “Typical” structure of a phospholipid molecule Two fatty acid chains and a phosphorus-containing group are attached to the glycerol backbone. Example Phosphatidylcholine Polar “head” Nonpolar “tail” (schematic phospholipid) Phosphorus-containing group (polar “head”) Glycerol backbone 2 fatty acid chains (nonpolar “tail”) Simplified structure of a steroid Four interlocking hydrocarbon rings form a steroid. Example Cholesterol (cholesterol is the basis for all steroids formed in the body) © 2013 Pearson Education, Inc.

Triglyceride formation Figure 2.16a Lipids. Triglyceride formation Three fatty acid chains are bound to glycerol by dehydration synthesis. + + Glycerol 3 fatty acid chains Triglyceride, or neutral fat 3 water molecules © 2013 Pearson Education, Inc.

Phosphorus-containing Figure 2.16b Lipids. “Typical” structure of a phospholipid molecule Two fatty acid chains and a phosphorus-containing group are attached to the glycerol backbone. Example Phosphatidylcholine Polar “head” Nonpolar “tail” (schematic phospholipid) Phosphorus-containing group (polar “head”) Glycerol backbone 2 fatty acid chains (nonpolar “tail”) © 2013 Pearson Education, Inc.

Four interlocking hydrocarbon rings Figure 2.16c Lipids. Simplified structure of a steroid Four interlocking hydrocarbon rings form a steroid. Example Cholesterol (cholesterol is the basis for all steroids formed in the body) © 2013 Pearson Education, Inc.

Table 2.2 Representative Lipids Found in the Body (1 of 2) © 2013 Pearson Education, Inc.

Table 2.2 Representative Lipids Found in the Body (2 of 2) © 2013 Pearson Education, Inc.

Figure 2.17 Amino acid structures. Amine group Acid group Generalized structure of all amino acids. Glycine is the simplest amino acid. Aspartic acid (an acidic amino acid) has an acid group (—COOH) in the R group. Lysine (a basic amino acid) has an amine group (—NH2) in the R group. Cysteine (a basic amino acid) has a sulfhydryl (—SH) group in the R group, which suggests that this amino acid is likely to participate in intramolecular bonding. © 2013 Pearson Education, Inc.

Figure 2.17a Amino acid structures. Amine group Acid group Generalized structure of all amino acids. © 2013 Pearson Education, Inc.

Figure 2.17b Amino acid structures. Glycine is the simplest amino acid. © 2013 Pearson Education, Inc.

Figure 2.17c Amino acid structures. Aspartic acid (an acidic amino acid) has an acid group (—COOH) in the R group. © 2013 Pearson Education, Inc.

Figure 2.17d Amino acid structures. Lysine (a basic amino acid) has an amine group (—NH2) in the R group. © 2013 Pearson Education, Inc.

Figure 2.17e Amino acid structures. Cysteine (a basic amino acid) has a sulfhydryl (—SH) group in the R group, which suggests that this amino acid is likely to participate in intramolecular bonding. © 2013 Pearson Education, Inc.

Figure 2.18 Amino acids are linked together by peptide bonds. Dehydration synthesis: The acid group of one amino acid is bonded to the amine group of the next, with loss of a water molecule. Peptide bond + Amino acid Amino acid Dipeptide Hydrolysis: Peptide bonds linking amino acids together are broken when water is added to the bond. © 2013 Pearson Education, Inc.

Figure 2.19 Levels of protein structure. Amino acid Amino acid Amino acid Amino acid Amino acid Primary structure: The sequence of amino acids forms the polypeptide chain. Secondary structure: The primary chain forms spirals (α-helices) and sheets (β-sheets). α-Helix:The primary chain is coiled to form a spiral structure, which is stabilized by hydrogen bonds. β-Sheet:The primary chain “zig-zags” back and forth forming a “pleated” sheet. Adjacent strands are held together by hydrogen bonds. Tertiary structure: Superimposed on secondary structure. α-Helices and/or β-sheets are folded up to form a compact globular molecule held together by intramolecular bonds. Tertiary structure of prealbumin (transthyretin), a protein that transports the thyroid hormone thyroxine in blood and cerebrospinal fluid. Quaternary structure: Two or more polypeptide chains, each with its own tertiary structure, combine to form a functional protein. Quaternary structure of a functional prealbumin molecule. Two identical prealbumin subunits join head to tail to form the dimer. © 2013 Pearson Education, Inc.

Figure 2.19a Levels of protein structure. Amino acid Amino acid Amino acid Amino acid Amino acid Primary structure: The sequence of amino acids forms the polypeptide chain. © 2013 Pearson Education, Inc.

Figure 2.19b Levels of protein structure. Secondary structure: The primary chain forms spirals (α-helices) and sheets (β-sheets). α-Helix: The primary chain is coiled to form a spiral structure, which is stabilized by hydrogen bonds. β-Sheet: The primary chain “zig-zags” back and forth forming a “pleated” sheet. Adjacent strands are held together by hydrogen bonds. © 2013 Pearson Education, Inc.

Figure 2.19c Levels of protein structure. Tertiary structure: Superimposed on secondary structure. α-Helices and/or β-sheets are folded up to form a compact globular molecule held together by intramolecular bonds. Tertiary structure of prealbumin (transthyretin), a protein that transports the thyroid hormone thyroxine in blood and cerebrospinal fluid. © 2013 Pearson Education, Inc.

Figure 2.19d Levels of protein structure. Quaternary structure: Two or more polypeptide chains, each with its own tertiary structure, combine to form a functional protein. Quaternary structure of a functional prealbumin molecule. Two identical prealbumin subunits join head to tail to form the dimer. © 2013 Pearson Education, Inc.

Table 2.3 Representative Types of Proteins in the Body (1 of 2) © 2013 Pearson Education, Inc.

Table 2.3 Representative Types of Proteins in the Body (2 of 2) © 2013 Pearson Education, Inc.

WITHOUT ENZYME WITH ENZYME Activation energy required Less activation Figure 2.20 Enzymes lower the activation energy required for a reaction. WITHOUT ENZYME WITH ENZYME Activation energy required Less activation energy required Energy Reactants Energy Reactants Product Product Progress of reaction Progress of reaction © 2013 Pearson Education, Inc.

Figure 2.21 Mechanism of enzyme action. Product (P) e.g., dipeptide Energy is absorbed; bond is formed. Substrates (S) e.g., amino acids Water is released. Peptide bond + Active site Enzyme-substrate complex (E-S) 1 2 Enzyme (E) Substrates bind at active site, temporarily forming an enzyme-substrate complex. The E-S complex undergoes internal rearrangements that form the product. Enzyme (E) 3 The enzyme releases the product of the reaction. © 2013 Pearson Education, Inc.

Figure 2.22 Structure of DNA. Sugar: Deoxyribose Base: Adenine (A) Phosphate Thymine (T) Sugar Phosphate Adenine nucleotide Thymine nucleotide Hydrogen bond Deoxyribose sugar Sugar- phosphate backbone Phosphate Adenine (A) Thymine (T) Cytosine (C) Guanine (G) © 2013 Pearson Education, Inc.

Figure 2.22a Structure of DNA. Sugar: Deoxyribose Base: Adenine (A) Phosphate Thymine (T) Sugar Phosphate Adenine nucleotide Thymine nucleotide © 2013 Pearson Education, Inc.

Figure 2.22b Structure of DNA. Hydrogen bond Deoxyribose sugar Sugar- phosphate backbone Phosphate Adenine (A) Thymine (T) Cytosine (C) Guanine (G) © 2013 Pearson Education, Inc.

Figure 2.22c Structure of DNA. © 2013 Pearson Education, Inc.

Table 2.4 Comparison of DNA and RNA © 2013 Pearson Education, Inc.

Figure 2.23 Structure of ATP (adenosine triphosphate). High-energy phosphate bonds can be hydrolyzed to release energy. Adenine Phosphate groups Ribose Adenosine Adenosine monophosphate (AMP) Adenosine diphosphate (ADP) Adenosine triphosphate (ATP) © 2013 Pearson Education, Inc.

Figure 2.24 Three examples of cellular work driven by energy from ATP. Solute + Membrane protein Transport work: ATP phosphorylates transport proteins, activating them to transport solutes (ions, for example) across cell membranes. + Relaxed smooth muscle cell Contracted smooth muscle cell Mechanical work: ATP phosphorylates contractile pro- teins in muscle cells so the cells can shorten. + Chemical work: ATP phosphorylates key reactants, providing energy to drive energy-absorbing chemical reactions. © 2013 Pearson Education, Inc.

Transport work: ATP phosphorylates transport proteins, Figure 2.24a Three examples of cellular work driven by energy from ATP. Solute + Membrane protein Transport work: ATP phosphorylates transport proteins, activating them to transport solutes (ions, for example) across cell membranes. © 2013 Pearson Education, Inc.

+ Relaxed smooth Contracted smooth muscle cell muscle cell Figure 2.24b Three examples of cellular work driven by energy from ATP. + Relaxed smooth muscle cell Contracted smooth muscle cell Mechanical work: ATP phosphorylates contractile proteins in muscle cells so the cells can shorten. © 2013 Pearson Education, Inc.

Chemical work: ATP phosphorylates key reactants, providing Figure 2.24c Three examples of cellular work driven by energy from ATP. + Chemical work: ATP phosphorylates key reactants, providing energy to drive energy-absorbing chemical reactions. © 2013 Pearson Education, Inc.