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Chapter 3 The Molecules of Life PowerPoint® Lectures for Campbell Essential Biology, Fourth Edition – Eric Simon, Jane Reece, and Jean Dickey Campbell Essential Biology with Physiology, Third Edition – Eric Simon, Jane Reece, and Jean Dickey Lectures by Chris C. Romero, updated by Edward J. Zalisko © 2010 Pearson Education, Inc. Biology and Society: Got Lactose? • Lactose is the main sugar found in milk. • Some adults exhibit lactose intolerance, the inability to properly digest lactose. • Lactose-intolerant individuals are unable to digest lactose properly. – Lactose is broken down by bacteria in the large intestine producing gas and discomfort. © 2010 Pearson Education, Inc. • There is no treatment for the underlying cause of lactose intolerance. • Affected people must – Avoid lactose-containing foods or – Take the enzyme lactase when eating dairy products © 2010 Pearson Education, Inc. ORGANIC COMPOUNDS • Carbon forms large, complex, and diverse molecules necessary for life’s functions. • Organic compounds are carbon-based molecules. • 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. © 2010 Pearson Education, Inc. Carbon skeletons vary in length Double bond Carbon skeletons may have double bonds, which can vary in location Carbon skeletons may be unbranched or branched Carbon skeletons may be arranged in rings Figure 3.1 Carbon skeletons vary in length Figure 3.1a Double bond Carbon skeletons may have double bonds, which can vary in location Figure 3.1b Carbon skeletons may be unbranched or branched Figure 3.1c Carbon skeletons may be arranged in rings Figure 3.1d Giant Molecules from Smaller Building Blocks • On a molecular scale, many of life’s molecules are gigantic, earning the name macromolecules. • Three categories of macromolecules are – Carbohydrates – Proteins – Nucleic acids © 2010 Pearson Education, Inc. • Most macromolecules are polymers. • Polymers are made by stringing together many smaller molecules called monomers. • A dehydration reaction – Links two monomers together – Removes a molecule of water • Organisms also have to break down macromolecules. • Hydrolysis – Breaks bonds between monomers – Adds a molecule of water © 2010 Pearson Education, Inc. Short polymer Monomer Dehydration reaction Hydrolysis Longer polymer a Building a polymer chain b Breaking a polymer chain Figure 3.4 Short polymer Monomer Dehydration reaction Longer polymer a Building a polymer chain Figure 3.4a Hydrolysis b Breaking a polymer chain Figure 3.4b LARGE BIOLOGICAL MOLECULES • There are four categories of large molecules in cells: – Carbohydrates – Lipids – Proteins – Nucleic acids © 2010 Pearson Education, Inc. Carbohydrates • Carbohydrates are sugars or sugar polymers. They include – Small sugar molecules in soft drinks – Long starch molecules in pasta and potatoes © 2010 Pearson Education, Inc. Monosaccharides • Monosaccharides are simple sugars that cannot be broken down by hydrolysis into smaller sugars. • Common examples are – Glucose in sports drinks – Fructose found in fruit • Glucose and fructose are isomers, molecules that have the same molecular formula but different structures. • Monosaccharides are the main fuels for cellular work. © 2010 Pearson Education, Inc. Glucose Fructose C6H12O6 C6H12O6 Isomers Figure 3.5a b Abbreviated ring structure a Linear and ring structures Figure 3.6 Disaccharides • A disaccharide is – A double sugar – Constructed from two monosaccharides – Formed by a dehydration reaction • Disaccharides include – Lactose in milk – Maltose in beer, malted milk shakes, and malted milk ball candy – Sucrose in table sugar © 2010 Pearson Education, Inc. Galactose Glucose Lactose Figure 3.7 • Sucrose is – The main carbohydrate in plant sap – Rarely used as a sweetener in processed foods • High-fructose corn syrup is made by a commercial process that converts natural glucose in corn syrup to much sweeter fructose. © 2010 Pearson Education, Inc. processed to extract Starch broken down into Glucose converted to sweeter Fructose added to foods as high-fructose corn syrup Ingredients: carbonated water, high-fructose corn syrup, caramel color, phosphoric acid, natural flavors Figure 3.8 Polysaccharides • Polysaccharides are – Complex carbohydrates – Made of long chains of sugar units and polymers of monosaccharides © 2010 Pearson Education, Inc. Glucose monomer Starch granules a Starch Glycogen granules b Glycogen Cellulose fibril Cellulose molecules c Cellulose Figure 3.9 • Starch is – Used by plant cells to store energy – Potatoes and grains are major sources. • Glycogen is – Used by animals cells to store energy – Converted to glucose when it is needed • Cellulose – Is the most abundant organic compound on Earth – Forms cable-like fibrils in the tough walls that enclose plants – Cannot be broken apart by most animals © 2010 Pearson Education, Inc. • Monosaccharides and disaccharides dissolve readily in water. • Cellulose does not dissolve readily in water. • Almost all carbohydrates are hydrophilic, or “water-loving,” adhering water to their surface. © 2010 Pearson Education, Inc. Lipids • Lipids are – Neither macromolecules nor polymers – Hydrophobic, unable to mix with water © 2010 Pearson Education, Inc. Oil (hydrophobic) Vinegar (hydrophilic) Figure 3.10 Fats • A typical fat, or triglyceride, consists of a glycerol molecule joined with three fatty acid molecules via a dehydration reaction. • Fats perform essential functions in the human body including – Energy storage – Cushioning – Insulation © 2010 Pearson Education, Inc. Fatty acid Glycerol (a) A dehydration reaction linking a fatty acid to glycerol (b) A fat molecule with a glycerol “head” and three energy-rich hydrocarbon fatty acid “tails” Figure 3.11 • If the carbon skeleton of a fatty acid has – Fewer than the maximum number of hydrogens, it is unsaturated – The maximum number of hydrogens, then it is saturated • A saturated fat has no double bonds, and all three of its fatty acids are saturated. © 2010 Pearson Education, Inc. • Most animal fats – Have a high proportion of saturated fatty acids – Can easily stack, tending to be solid at room temperature – Contribute to atherosclerosis, a condition in which lipidcontaining plaques build up within the walls of blood vessels – Most plant oils tend to be low in saturated fatty acids and liquid at room temperature. © 2010 Pearson Education, Inc. • Hydrogenation – Adds hydrogen – Converts unsaturated fats to saturated fats – Makes liquid fats solid at room temperature – Creates trans fat, a type of unsaturated fat that is even less healthy than saturated fats © 2010 Pearson Education, Inc. TYPES OF FATS Saturated Fats Unsaturated Fats Margarine INGREDIENTS: SOYBEAN OIL, FULLY HYDROGENATED COTTONSEED OIL, PARTIALLY HYDROGENATED COTTONSEED OIL AND SOYBEAN OILS, MONO AND DIGLYCERIDES, TBHO AND CITRIC ACID Plant oils Trans fats ANTIOXIDANTS Omega-3 fats Figure 3.12 Steroids • Steroids are very different from fats in structure and function. – The carbon skeleton is bent to form four fused rings. • Cholesterol is – A key component of cell membranes – The “base steroid” from which your body produces other steroids, such as estrogen and testosterone © 2010 Pearson Education, Inc. Cholesterol Testosterone A type of estrogen Figure 3.13 Proteins • Proteins – Are polymers constructed from amino acid monomers – Perform most of the tasks the body needs to function – Form enzymes, chemicals that change the rate of a chemical reaction without being changed in the process © 2010 Pearson Education, Inc. MAJOR TYPES OF PROTEINS Structural Proteins Storage Proteins Contractile Proteins Transport Proteins Enzymes Figure 3.15 The Monomers of Proteins: Amino Acids • All proteins are constructed from a common set of 20 kinds of amino acids. • Each amino acid consists of a central carbon atom bonded to four covalent partners in which three of those attachment groups are common to all amino acids. © 2010 Pearson Education, Inc. Amino group Carboxyl group Side group a The general structure of an amino acid Hydrophobic side group Hydrophilic side group Leucine Serine b Examples of amino acids with hydrophobic and hydrophilic side groups Figure 3.16 Proteins as Polymers • Cells link amino acids together by dehydration reactions, forming peptide bonds and creating long chains of amino acids called polypeptides. © 2010 Pearson Education, Inc. Carboxyl group Amino group Side group Side group Amino acid Amino acid Dehydration reaction Side group Side group Peptide bond Figure 3.17-2 • Your body has tens of thousands of different kinds of protein. • Proteins differ in their arrangement of amino acids. • The specific sequence of amino acids in a protein is its primary structure. © 2010 Pearson Education, Inc. 15 5 1 10 30 35 20 25 45 40 50 55 65 60 70 75 Amino acid 85 80 95 100 90 110 115 105 125 120 129 Figure 3.18 SEM 1 2 Normal red blood cell 3 4 5 6 7. . . 146 Normal hemoglobin SEM a Normal hemoglobin 1 Sickled red blood cell 2 3 4 5 6 7. . . 146 Sickle-cell hemoglobin b Sickle-cell hemoglobin Figure 3.19 Protein Shape • A functional protein consists of one or more polypeptide chains, precisely folded and coiled into a molecule of unique shape. • A protein’s three-dimensional shape – Recognizes and binds to another molecule – Enables the protein to carry out its specific function in a cell © 2010 Pearson Education, Inc. Target Protein Figure 3.21 What Determines Protein Shape? • A protein’s shape is sensitive to the surrounding environment. • Unfavorable temperature and pH changes can cause denaturation of a protein, in which it unravels and loses its shape. • High fevers (above 104º F) in humans can cause some proteins to denature. • Misfolded proteins are associated with – Alzheimer’s disease – Mad cow disease – Parkinson’s disease © 2010 Pearson Education, Inc. Nucleic Acids • Nucleic acids – Are macromolecules that provide the directions for building proteins – Include DNA and RNA – Are the genetic material that organisms inherit from their parents © 2010 Pearson Education, Inc. • DNA resides in cells in long fibers called chromosomes. • A gene is a specific stretch of DNA that programs the amino acid sequence of a polypeptide. • The chemical code of DNA must be translated from “nucleic acid language” to “protein language.” © 2010 Pearson Education, Inc. Gene DNA Nucleic acids RNA Amino acid Protein Figure 3.22 • Nucleic acids are polymers of nucleotides. • Each nucleotide has three parts: – A five-carbon sugar – A phosphate group – A nitrogenous base © 2010 Pearson Education, Inc. Nitrogenous base A, G, C, or T Thymine T Phosphate group Phosphate Base Sugar deoxyribose a Atomic structure Sugar b Symbol used in this book Figure 3.23 • Each DNA nucleotide has one of the following bases: – Adenine (A) – Guanine (G) – Thymine (T) – Cytosine (C) © 2010 Pearson Education, Inc. Adenine A Thymine T Guanine G Cytosine C Figure 3.24a Adenine A Guanine G Thymine T Cytosine C Space-filling model of DNA Figure 3.24b Sugar-phosphate backbone Base Nucleotide pair Hydrogen bond Bases a DNA strand polynucleotide b Double helix two polynucleotide strands Figure 3.25 • Two strands of DNA join together to form a double helix. • Bases along one DNA strand hydrogen-bond to bases along the other strand. • The functional groups hanging off the base determine which bases pair up: – A only pairs with T. – G can only pair with C. © 2010 Pearson Education, Inc. • RNA, ribonucleic acid, is different from DNA. – RNA is usually single-stranded but DNA usually exists as a double helix. – RNA uses the sugar ribose and the base uracil (U) instead of thymine (T). © 2010 Pearson Education, Inc. Nitrogenous base A, G, C, or U Uracil U Phosphate group Sugar ribose Figure 3.26 Large biological molecules Carbohydrates Functions Components Examples Monosaccharides: glucose, fructose Disaccharides: lactose, sucrose Polysaccharides: starch, cellulose Dietary energy; storage; plant structure Monosaccharide Lipids Long-term energy storage fats; hormones steroids Fatty acid Glycerol Components of a triglyceride Amino group Proteins Enzymes, structure, storage, contraction, transport, and others Fats triglycerides; Steroids testosterone, estrogen Carboxyl group Side group Lactase an enzyme, hemoglobin a transport protein Amino acid Phosphate Base Nucleic acids Information storage DNA, RNA Sugar Nucleotide Figure UN3-2 Carbohydrates Functions Components Examples Monosaccharides: glucose, fructose Disaccharides: lactose, sucrose Polysaccharides: starch, cellulose Dietary energy; storage; plant structure Monosaccharide Figure UN3-2a Lipids Functions Long-term energy storage fats; hormones steroids Components Fatty acid Glycerol Components of a triglyceride Examples Fats triglycerides; Steroids testosterone, estrogen Figure UN3-2b Proteins Functions Components Amino group Enzymes, structure, storage, contraction, transport, and others Examples Carboxyl group Side group Lactase an enzyme, hemoglobin a transport protein Amino acid Figure UN3-2c Nucleic acids Functions Components Examples Phosphate Base Information storage DNA, RNA Sugar Nucleotide Figure UN3-2d Chapter 4 A Tour of the Cell PowerPoint® Lectures for Campbell Essential Biology, Fourth Edition – Eric Simon, Jane Reece, and Jean Dickey Campbell Essential Biology with Physiology, Third Edition – Eric Simon, Jane Reece, and Jean Dickey Lectures by Chris C. Romero, updated by Edward J. Zalisko © 2010 Pearson Education, Inc. Biology and Society: Drugs That Target Bacterial Cells • Antibiotics were first isolated from mold in 1928. • The widespread use of antibiotics drastically decreased deaths from bacterial infections. • Most antibiotics kill bacteria while minimally harming the human host by binding to structures found only on bacterial cells. • Some antibiotics bind to the bacterial ribosome, leaving human ribosomes unaffected. • Other antibiotics target enzymes found only in the bacterial cells. © 2010 Pearson Education, Inc. Colorized TEM © 2010 Pearson Education, Inc. Figure 4.00 THE MICROSCOPIC WORLD OF CELLS • Organisms are either – Single-celled, such as most prokaryotes and protists or – Multicelled, such as plants, animals, and most fungi © 2010 Pearson Education, Inc. LM Light Micrograph (LM) (for viewing living cells) Light micrograph of a protist, Paramecium © 2010 Pearson Education, Inc. Figure 4.1a Colorized SEM Scanning Electron Micrograph (SEM) (for viewing surface features) Scanning electron micrograph of Paramecium © 2010 Pearson Education, Inc. Figure 4.1b Colorized TEM Transmission Electron Micrograph (TEM) (for viewing internal structures) Transmission electron micrograph of Paramecium © 2010 Pearson Education, Inc. Figure 4.1c 10 m 1m Length of some nerve and muscle cells 10 cm Chicken egg Unaided eye Human height 1 cm Frog eggs Plant and animal cells 10 mm 1 mm 100 nm Nucleus Most bacteria Mitochondrion Smallest bacteria Viruses Ribosomes 10 nm Electron microscope 100 mm Light microscope 1 mm Proteins Lipids 1 nm 0.1 nm © 2010 Pearson Education, Inc. Small molecules Atoms Figure 4.3 The Two Major Categories of Cells • The countless cells on earth fall into two categories: – Prokaryotic cells — Bacteria and Archaea – Eukaryotic cells — plants, fungi, and animals • All cells have several basic features. – They are all bound by a thin plasma membrane. – All cells have DNA and ribosomes, tiny structures that build proteins. © 2010 Pearson Education, Inc. • Prokaryotic cells are older than eukaryotic cells. – Prokaryotes appeared about 3.5 billion years ago. – Eukaryotes appeared about 2.1 billion years ago. • Prokaryotic and eukaryotic cells have important differences. © 2010 Pearson Education, Inc. • Prokaryotes – Are smaller than eukaryotic cells – Lack internal structures surrounded by membranes – Lack a nucleus – Have a rigid cell wall • Eukaryotes – Only eukaryotic cells have organelles, membrane-bound structures that perform specific functions. – The most important organelle is the nucleus, which houses most of a eukaryotic cell’s DNA. © 2010 Pearson Education, Inc. Plasma membrane (encloses cytoplasm) Cell wall (provides Rigidity) Capsule (sticky coating) Colorized TEM Prokaryotic flagellum (for propulsion) Ribosomes (synthesize proteins) Nucleoid (contains DNA) Pili (attachment structures) © 2010 Pearson Education, Inc. Figure 4.4 Plasma membrane (encloses cytoplasm) Cell wall (provides rigidity) Capsule (sticky coating) Prokaryotic flagellum (for propulsion) Ribosomes (synthesize proteins) Nucleoid (contains DNA) Pili (attachment structures) © 2010 Pearson Education, Inc. Figure 4.4a Colorized TEM © 2010 Pearson Education, Inc. Figure 4.4b An Overview of Eukaryotic Cells • Eukaryotic cells are fundamentally similar. • The region between the nucleus and plasma membrane is the cytoplasm. • The cytoplasm consists of various organelles suspended in fluid. • Unlike animal cells, plant cells have – Protective cell walls – Chloroplasts, which convert light energy to the chemical energy of food © 2010 Pearson Education, Inc. Ribosomes Cytoskeleton Centriole Lysosome Not in most plant cells Flagellum Plasma membrane Nucleus Mitochondrion Rough endoplasmic reticulum (ER) Golgi apparatus Idealized animal cell © 2010 Pearson Education, Inc. Smooth endoplasmic reticulum (ER) Figure 4.5a Cytoskeleton Central vacuole Cell wall Chloroplast Mitochondrion Nucleus Not in animal cells Rough endoplasmic reticulum (ER) Ribosomes Plasma membrane Smooth endoplasmic reticulum (ER) Channels between cells Golgi apparatus Idealized plant cell © 2010 Pearson Education, Inc. Figure 4.5b MEMBRANE STRUCTURE • The plasma membrane separates the living cell from its nonliving surroundings. • The membranes of cells are composed mostly of – Lipids – Proteins • The lipids belong to a special category called phospholipids. • Phospholipids form a two-layered membrane, the phospholipid bilayer. © 2010 Pearson Education, Inc. Outside of cell Hydrophilic head Hydrophobic tail Phospholipid Cytoplasm (inside of cell) (a) Phospholipid bilayer of membrane © 2010 Pearson Education, Inc. Figure 4.6a Outside of cell Proteins Hydrophilic region of protein Phospholipid bilayer Hydrophilic head Hydrophobic tail Hydrophobic regions of protein Cytoplasm (inside of cell) (b) Fluid mosaic model of membrane © 2010 Pearson Education, Inc. Figure 4.6b • The plasma membrane is a fluid mosaic: – Fluid because molecules can move freely past one another – A mosaic because of the diversity of proteins in the membrane © 2010 Pearson Education, Inc. Cell Surfaces • Plant cells have rigid cell walls surrounding the membrane. • Plant cell walls – Are made of cellulose – Protect the cells – Maintain cell shape – Keep the cells from absorbing too much water © 2010 Pearson Education, Inc. THE NUCLEUS AND RIBOSOMES: GENETIC CONTROL OF THE CELL • The nucleus is the chief executive of the cell. – Genes in the nucleus store information necessary to produce proteins. – Proteins do most of the work of the cell. © 2010 Pearson Education, Inc. Structure and Function of the Nucleus • The nucleus is bordered by a double membrane called the nuclear envelope. • Pores in the envelope allow materials to move between the nucleus and cytoplasm. • The nucleus contains a nucleolus where ribosomes are made. © 2010 Pearson Education, Inc. Nuclear envelope Nucleolus Surface of nuclear envelope © 2010 Pearson Education, Inc. Pore TEM Chromatin TEM Ribosomes Nuclear pores Figure 4.8 Ribosomes • Ribosomes are responsible for protein synthesis. • Ribosome components are made in the nucleolus but assembled in the cytoplasm. • Ribosomes may assemble proteins: – Suspended in the fluid of the cytoplasm or – Attached to the outside of an organelle called the endoplasmic reticulum © 2010 Pearson Education, Inc. Ribosome mRNA Protein © 2010 Pearson Education, Inc. Figure 4.10 The Endoplasmic Reticulum • The endoplasmic reticulum (ER) is one of the main manufacturing facilities in a cell. • The ER – Produces an enormous variety of molecules – Is composed of smooth and rough ER © 2010 Pearson Education, Inc. Nuclear envelope Ribosomes TEM Rough ER © 2010 Pearson Education, Inc. Smooth ER Ribosomes Figure 4.13 Rough ER • The “rough” in the rough ER is due to ribosomes that stud the outside of the ER membrane. • These ribosomes produce membrane proteins and secretory proteins. • After the rough ER synthesizes a molecule, it packages the molecule into transport vesicles. © 2010 Pearson Education, Inc. Proteins are often modified in the ER. Secretory proteins depart in transport vesicles. Ribosome Vesicles bud off from the ER. Transport vesicle Protein A ribosome links amino acids into a polypeptide. © 2010 Pearson Education, Inc. Rough ER Polypeptide Figure 4.14 Smooth ER • The smooth ER – Lacks surface ribosomes – Produces lipids, including steroids – Helps liver cells detoxify circulating drugs © 2010 Pearson Education, Inc. The Golgi Apparatus • The Golgi apparatus – Works in partnership with the ER – Receives, refines, stores, and distributes chemical products of the cell © 2010 Pearson Education, Inc. Transport vesicle from rough ER “Receiving” side of Golgi apparatus New vesicle forming Transport vesicle from the Golgi “Shipping” side of Golgi apparatus Plasma membrane © 2010 Pearson Education, Inc. Figure 4.15a Colorized SEM “Receiving” side of Golgi apparatus New vesicle forming © 2010 Pearson Education, Inc. Figure 4.15b Lysosomes • A lysosome is a sac of digestive enzymes found in animal cells. • Enzymes in a lysosome can break down large molecules such as – Proteins – Polysaccharides – Fats – Nucleic acids • Lysosomes can also – Destroy harmful bacteria – Break down damaged organelles © 2010 Pearson Education, Inc. • Lysosomes have several types of digestive functions. – Many cells engulf nutrients in tiny cytoplasmic sacs called food vacuoles. – These food vacuoles fuse with lysosomes, exposing food to enzymes to digest the food. – Small molecules from digestion leave the lysosome and nourish the cell. © 2010 Pearson Education, Inc. Plasma membrane Digestive enzymes Lysosome Lysosome Digestion Food vacuole Vesicle containing damaged organelle (a) Lysosome digesting food Digestion (b) Lysosome breaking down the molecules of damaged organelles Organelle fragment Vesicle containing two damaged organelles TEM Organelle fragment © 2010 Pearson Education, Inc. Figure 4.16 • Central vacuoles of plants – Store nutrients – Absorb water – May contain pigments or poisons © 2010 Pearson Education, Inc. TEM Vacuole filling with water TEM Vacuole contracting (a) Contractile vacuole in Paramecium © 2010 Pearson Education, Inc. Figure 4.17a Colorized TEM Central vacuole (b) Central vacuole in a plant cell © 2010 Pearson Education, Inc. Figure 4.17b Golgi apparatus Rough ER Transport vesicle Transport vesicles carry enzymes and other proteins from the rough ER to the Golgi for processing. Transport vesicle Plasma membrane Secretory protein Some products are secreted from the cell. © 2010 Pearson Education, Inc. Vacuole Lysosomes carrying digestive enzymes can Lysosome fuse with other vesicles. Vacuoles store some cell products. Figure 4.18a CHLOROPLASTS AND MITOCHONDRIA: ENERGY CONVERSION • Cells require a constant energy supply to perform the work of life. © 2010 Pearson Education, Inc. Chloroplasts • Most of the living world runs on the energy provided by photosynthesis. • Photosynthesis is the conversion of light energy from the sun to the chemical energy of sugar. • Chloroplasts are the organelles that perform photosynthesis. – Grana, stroma, thylakoids, etc… © 2010 Pearson Education, Inc. Inner and outer membranes Space between membranes Granum TEM Stroma (fluid in chloroplast) © 2010 Pearson Education, Inc. Figure 4.19 Mitochondria • Mitochondria are the sites of cellular respiration, which produce ATP from the energy of food molecules. • Mitochondria are found in almost all eukaryotic cells. • An envelope of two membranes encloses the mitochondrion. © 2010 Pearson Education, Inc. TEM Outer membrane Inner membrane Cristae Matrix Space between membranes © 2010 Pearson Education, Inc. Figure 4.20 THE CYTOSKELETON: CELL SHAPE AND MOVEMENT • The cytoskeleton is a network of fibers extending throughout the cytoplasm. • The cytoskeleton – Provides mechanical support to the cell – Maintains its shape © 2010 Pearson Education, Inc. LM (a) Microtubules in the cytoskeleton LM (b) Microtubules and movement © 2010 Pearson Education, Inc. Figure 4.21 Cilia and Flagella • Cilia and flagella aid in movement. – Flagella propel the cell in a whiplike motion. – Cilia move in a coordinated back-and-forth motion. – Cilia and flagella have the same basic architecture. • Cilia may extend from nonmoving cells. • On cells lining the human trachea, cilia help sweep mucus out of the lungs. © 2010 Pearson Education, Inc. Colorized SEM (a) Flagellum of a human sperm cell © 2010 Pearson Education, Inc. Colorized SEM Colorized SEM (b) Cilia on a protist (c) Cilia lining the respiratory tract Figure 4.22 Evolution Connection: The Evolution of Antibiotic Resistance • Many antibiotics disrupt cellular structures of invading microorganisms. • Introduced in the 1940s, penicillin worked well against such infections. • But over time, bacteria that were resistant to antibiotics were favored. • The widespread use and abuse of antibiotics continues to favor bacteria that resist antibiotics. © 2010 Pearson Education, Inc.