Cohesion Collectively, hydrogen bonds hold water molecules together, a phenomenon called cohesion Cohesion helps the transport of water against gravity in plants Adhesion is an attraction between different substances, for example, between water and plant cell walls Animation: Water Transport Animation: Water Transport Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 1

Fig. 3-3 Water-conducting cells Adhesion Cohesion 150 µm Direction of water movement 2

Universal Solvent A solution is a liquid that is a homogeneous mixture of substances A solvent is the dissolving agent of a solution The solute is the substance that is dissolved An aqueous solution is one in which water is the solvent Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 3

Fig. 3-7 Cl – Na Cl – – – – – – – – – Na + – – – + 4

The Formation of Bonds with Carbon With four valence electrons, carbon can form four covalent bonds with a variety of atoms This tetravalence makes large, complex molecules possible In molecules with multiple carbons, each carbon bonded to four other atoms has a tetrahedral shape However, when two carbon atoms are joined by a double bond, the molecule has a flat shape Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 5

Fig. 4-3 Name Molecular Formula Structural Formula Ball-and-Stick Model Space-Filling Model (a) Methane (b) Ethane (c) Ethene (ethylene) 6

ATP: An Important Source of Energy for Cellular Processes One phosphate molecule, adenosine triphosphate (ATP), is the primary energy- transferring molecule in the cell ATP consists of an organic molecule called adenosine attached to a string of three phosphate groups Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 7

Fig. 4-UN4 PPPP i PP Adenosine Energy ADPATP Inorganic phosphate Reacts with H 2 O 8

Carbohydrates serve as fuel and building material Carbohydrates include sugars and the polymers of sugars The simplest carbohydrates are monosaccharides, or single sugars Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 9

Starch Plants store surplus starch as granules within chloroplasts and other plastids Cellulose is a major component of the tough wall of plant cells Chitin provides structural support for the cell walls of many fungi Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 10

Concept 5.3: Lipids are a diverse group of hydrophobic molecules Lipids store energy and maintain membranes Lipids are hydrophobic because  they consist mostly of hydrocarbons, which form nonpolar covalent bonds Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 11

Saturated fatty acids have the maximum number of hydrogen atoms possible and no double bonds Unsaturated fatty acids have one or more double bonds Animation: Fats Animation: Fats Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 12

Four Levels of Protein Structure The primary structure of a protein is its unique sequence of amino acids Secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain Tertiary structure is determined by interactions among various side chains (R groups) Quaternary structure results when a protein consists of multiple polypeptide chains Animation: Protein Structure Introduction Animation: Protein Structure Introduction Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 13

Fig Primary structure Secondary and tertiary structures Quaternary structure Normal hemoglobin (top view) Primary structure Secondary and tertiary structures Quaternary structure Function  subunit Molecules do not associate with one another; each carries oxygen. Red blood cell shape Normal red blood cells are full of individual hemoglobin moledules, each carrying oxygen. 10 µm Normal hemoglobin     Val His Leu ThrPro Glu Red blood cell shape  subunit Exposed hydrophobic region Sickle-cell hemoglobin   Molecules interact with one another and crystallize into a fiber; capacity to carry oxygen is greatly reduced.   Fibers of abnormal hemoglobin deform red blood cell into sickle shape. 10 µm Sickle-cell hemoglobin GluPro Thr Leu His Val

The Roles of Nucleic Acids There are two types of nucleic acids: – Deoxyribonucleic acid (DNA) directs synthesis of messenger RNA – Ribonucleic acid (RNA) controls protein synthesis Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 15

Fig mRNA Synthesis of mRNA in the nucleus DNA NUCLEUS mRNA CYTOPLASM Movement of mRNA into cytoplasm via nuclear pore Ribosome Amino acids Polypeptide Synthesis of protein

Concept 5.2: Carbohydrates serve as fuel and building material Carbohydrates include sugars and the polymers of sugars The simplest carbohydrates are monosaccharides, or single sugars Carbohydrate macromolecules are polysaccharides, polymers composed of many sugar building blocks Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 17

Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods Chitin also provides structural support for the cell walls of many fungi Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 18

Concept 5.3: Lipids are a diverse group of hydrophobic molecules Lipids are the one class of large biological molecules that do not form polymers The unifying feature of lipids is having little or no affinity for water Lipids are hydrophobic because  they consist mostly of hydrocarbons, which form nonpolar covalent bonds The most biologically important lipids are fats, phospholipids, and steroids Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 19

Fatty acids vary in length (number of carbons) and in the number and locations of double bonds Saturated fatty acids have the maximum number of hydrogen atoms possible and no double bonds Unsaturated fatty acids have one or more double bonds Animation: Fats Animation: Fats Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 20

Four Levels of Protein Structure The primary structure of a protein is its unique sequence of amino acids Secondary structure, found in most proteins, consists of coils and folds in the polypeptide chain Tertiary structure is determined by interactions among various side chains (R groups) Quaternary structure results when a protein consists of multiple polypeptide chains Animation: Protein Structure Introduction Animation: Protein Structure Introduction Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 21

Fig Primary structure Secondary and tertiary structures Quaternary structure Normal hemoglobin (top view) Primary structure Secondary and tertiary structures Quaternary structure Function  subunit Molecules do not associate with one another; each carries oxygen. Red blood cell shape Normal red blood cells are full of individual hemoglobin moledules, each carrying oxygen. 10 µm Normal hemoglobin     Val His Leu ThrPro Glu Red blood cell shape  subunit Exposed hydrophobic region Sickle-cell hemoglobin   Molecules interact with one another and crystallize into a fiber; capacity to carry oxygen is greatly reduced.   Fibers of abnormal hemoglobin deform red blood cell into sickle shape. 10 µm Sickle-cell hemoglobin GluPro Thr Leu His Val

What Determines Protein Structure? In addition to primary structure, physical and chemical conditions can affect structure Alterations in pH, salt concentration, temperature, or other environmental factors can cause a protein to unravel This loss of a protein’s native structure is called denaturation A denatured protein is biologically inactive Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 23

Fig Normal protein Denatured protein Denaturation Renaturation 24

The Roles of Nucleic Acids There are two types of nucleic acids: – Deoxyribonucleic acid (DNA) – Ribonucleic acid (RNA) DNA provides directions for its own replication DNA directs synthesis of messenger RNA (mRNA) and, through mRNA, controls protein synthesis Protein synthesis occurs in ribosomes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings 25

Fig mRNA Synthesis of mRNA in the nucleus DNA NUCLEUS mRNA CYTOPLASM Movement of mRNA into cytoplasm via nuclear pore Ribosome Amino acids Polypeptide Synthesis of protein