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CHAPTER 3 CELL STRUCTURE AND FUNCTION BEHAVIORAL OBJECTIVES 1. Explain how surface area-to-volume ratio limits the size of cells. [3.1, p.42] 2. Recognize that different features of the cell are best observed with different types of microscopes. [3.1, pp.4243, Fig. 3.2] 3. Describe the chemical structure of the plasma membrane. [3.2, pp.44-46, Fig. 3.4] 4. Explain the diverse ways cells use to control passage of materials through the plasma membrane. [3.2, pp. 4648, Fig. 3.6, Table 3.2] 5. Predict the results of placing a cell in solutions of various tonicity. [3.2, p.47, Fig. 3.5] 6. Describe the structure of the nucleus and its importance to the cell. [3.2, p.49, Fig. 3.7] 7. Discuss the features and importance of ribosomes. [3.2, p.50, Fig. 3.8] 8. Explain the relationship among the endoplasmic reticulum, the Golgi apparatus, and lysosomes. [3.2, pp. 5052, Figs. 3.8 & 3.9] 9. Describe the structure and function of the mitochondria within the cell. [3.2, p. 52, Fig. 3.10] 10. Describe the structure and function of the cytoskeleton within the cytoplasm. [3.2, p.53] 11. Describe the relationship between centrioles and cilia or flagella. [3.2, pp. 53-54, Figs. 3.11 & 3.12] 12. Understand the functioning of a metabolic pathway and the importance of enzymes within it. [3.3, p. 55] 13. Describe a generalized equation for an enzymatic reaction. [3.3, p.54, Fig. 3.13] 14. Explain the function of coenzymes. [3.3, p. 55] 15. Associate the summary chemical reaction of aerobic cellular respiration with glycolysis, the Krebs cycle, and the electron transport system. [3.3, p. 55, Fig. 3.14, Table 3.4] 16. Outline the chemical reactions that take place during aerobic cellular respiration, and relate the results to the three metabolic pathways involved. [3.3, p. 56, Fig. 3.14] 17. Explain the relationship between the mitochondria and the Krebs cycle and electron transport system. [3.3, pp. 52-53, 55-56] 18. Compare the conditions required for aerobic cellular respiration with those that result in fermentation. [3.3, p. 57] 19. Understand and use the bold-faced and italicized terms included in this chapter. [Understanding Key Terms, p.59] EXTENDED LECTURE OUTLINE 3.1 Cell Size All living things are composed of cells, and new cells arise only from preexisting ones. Cells are small to maintain an optimal surface area to volume ratio. Microscopy and Cell Structure The compound light microscope passes light rays through specimens and uses glass lenses to view objects. The transmission electron microscope passes electrons through a specimen, focuses with magnetic lenses, and projects images onto a fluorescent screen or photographic film. The scanning electron microscope passes a beam of electrons over the surface of a metal-coated specimen, collecting them to produce a television-type picture on a screen. Mader VRL CD-ROM Image 0056l.jpg (Fig. 3.1) Image 0057l.jpg (Fig. TA3.1) Image 0058al.jpg (Fig. 3.2a) Image 0058bl.jpg (Fig. 3.2b) Image 0058cl.jpg (Fig. 3.2c) 11 Dynamic Human CD-ROM Human Body/Anatomy/Cell Shape Human Body/Anatomy/Cell Size Mader ESP Modules Online Cells/Cell Structures/Surface to Volume Transparencies 35 (Fig. TA3.1) 36 (Fig. 3.2a) 37 (Fig. 3.2b) 38 (Fig. 3.2c) 3.2 Cellular Organization A human cell is bounded by a plasma membrane which encloses a central nucleus surrounded by cytoplasm. The cytoplasm contains organelles, small membranous structures, and the cytoskeleton. The Plasma Membrane Plasma membrane is a bilayer of phospholipids with embedded or attached proteins. Glycoproteins and glycolipids serve as identification markers. Embedded proteins may serve as hormone receptors, transport channels, and enzymes in metabolic reactions. Plasma Membrane Functions Keeps a cell intact and being selectively permeable, it regulates the entrance and exit of molecules. Diffusion Diffusion is the random movement of molecules from an area of higher concentration to one of lower concentration. Osmosis Osmosis is the diffusion of water across a plasma membrane. Transport by Carriers Transport by carriers occurs in two manners. In facilitated transport a protein carrier helps a molecule across the membrane, using no energy. In active transport, a protein carrier transports a molecule but requires energy . Endocytosis and Exocytosis Endocytosis occurs as the plasma membrane forms a vesicle around a particle. Exocytosis is the reverse process. The Nucleus The nucleus DNA directs protein synthesis in the cytoplasm. It contains one or more nucleoli, where ribosomal RNA (rRNA) is manufactured. The nuclear envelope is a double membrane with nuclear pores. Ribosomes Ribosomes are a mix of rRNA and proteins. They are the sites of protein synthesis in the cytoplasm. Membranous Canals and Vesicles The endomembrane system consists of the nuclear envelope, endoplasmic reticulum, the Golgi apparatus, and several vesicles. The Endoplasmic Reticulum The endoplasmic reticulum (ER) is a series of membranes that form tubular channels within the cytoplasm. Rough ER (with ribosomes) specializes in protein synthesis. Smooth ER produces different compounds in different cells. The Golgi Apparatus The Golgi apparatus, a stack of flattened vacuoles with vesicles near the edges, packages, stores, and distributes the proteins the ER produces. Lysosomes The Golgi apparatus produces lysosomes, which contain hydrolytic enzymes that digest unwanted materials inside the cell, including worn-out cell parts. 12 Mitochondria Mitochondria are organelles bounded by a double membrane. The inner membrane is folded into cristae. The gellike material between the cristae is matrix. Mitochondria convert the energy stored in glucose into ATP molecules in a process called aerobic cellular respiration. The Cytoskeleton Filamentous protein structures, microtubules, and actin filaments form a cytoskeleton that serves as a framework for the cell's interior. Centrioles Centrioles are short cyclinders with a 9 + 0 arrangement of microtubules that occur in pairs within the centrome, the major microtubule organizing center of the cell. Centrioles also give rise to basal bodies that direct the formation of cilia and flagella. Cilia and Flagella Cilia and flagella are hairlike projections of cells responsible for locomotion. Each cilium and flagellum has a basal body at its base. Mader VRL CD-ROM Image 0059a.jpg (Fig. 3.3) Image 0059bl.jpg (Fig 3.3) Image 0059cl.jpg (Fig. 3.3) Image 0060l.jpg (Fig. 3.3b) Image 0061al.jpg (Fig. 3.4) Image 0061bl.jpg (Fig. 3.4) Image 0062l.jpg (Fig. 3.5) Image 0063l.jpg (Fig. 3.6) Image 0064al.jpg (Fig. 3.7) Image 0064bl.jpg (Fig. 3.7) Image 0064cl.jpg (Fig. 3.7) Image 0065l.jpg (Fig. 3.8) Image 0066l.jpg (Fig. 3.9) Image 0067l.jpg (Fig. 3.9) Image 0068l.jpg (Fig. 3.10) Image 0069l.jpg (Fig. TA3.2) Image 0070l.jpg (Fig. 3.11) Image 0071l.jpg (Fig. 3.12) Dynamic Human CD-ROM Human Body/Anatomy/Cell Components Life Science Animations VRL 2.0 Cell/Membrane Structure and Function/How Molecules Cross the Plasma Membrane Cell/Membrane Structure and Function/Diffusion Cell/Membrane Structure and Function/Diffusion_1 Cell/Membrane Structure and Function/Diffusion_2 Cell/Membrane Structure and Function/Osmosis_1 Cell/Membrane Structure and Function/Osmosis_2 Cell/Membrane Structure and Function/Osmosis_3 Cell/Membrane Structure and Function/Facilitated Diffusion Cell/Membrane Structure and Function/Transport Moves Substances Cell/Membrane Structure and Function/Active transport Cell/Membrane Structure and Function/Sodium-Potassium Pump_1 13 Life Science Animations VRL 2.0, con’t. Mader ESP Modules Online Transparencies Cell/Membrane Structure and Function/Sodium-Potassium Pump_2 Cell/Membrane Structure and Function/Cotransport Cell/Membrane Structure and Function/Endocytosis and Exocytosis Cell/Cell Structure and Function/Animal Cell Anatomy Cell/Cell Structure and Function/Rough Endoplasmic Reticulum (ER) Cell/Cell Structure and Function/Golgi apparatus Cell/Cell Structure and Function/Secretion Cell/Cell Respiration/Organization of Cristae Cells/Cell Structures/Eukaryotes Cells/Cell Membrane/Membrane Structure Cells/Cell Membrane/Diffusion Cells/Cell Membrane/Osmosis Cells/Cell Membrane/Facilitated Diffusion Cells/Cell Membrane/Active Transport Cells/Cell Membrane/Exo-Endocytosis Cells/Cell Membrane/Cell Interactions Cells/Cell Structures/Endomembrane Cells/Cell Structures/Energy Organelles Cells/Cell Structures/Cytoskeleton 39 (Fig. 3.3a) 40 (Fig. 3.4) 41 (Fig. 3.5) 42 (Fig. 3.6) 43 (Fig. 3.7) 44 (Fig. 3.8) 45 (Fig. 3.9) 46 (Fig. 3.10) 47 (Fig. 3.11) 3.3 Cellular Metabolism Chemical reactions in cell are organized into metabolic pathways where every reaction has its own enzyme. Enzymes and Coenzymes Enzymes are named for their substrates and have an active site specific for the substrate. Many enzymes have nonprotein molecules, called coenzymes, to assist them. Some coenzymes, like NAD, remove hydrogen from substrates. Cellular Respiration Glucose breaks down into carbon dioxide and water requires three subpathways: Glycolysis, the Krebs cycle, and the electron transport system. Glycolysis needs no oxygen and takes place in the cytoplasm of the cell. During glycolysis, glucose breaks down into two molecules of pyruvate, with a net gain of 2 ATP. A transition reaction converts pyruvate to active acetate that can enter the mitochondrion and the Krebs cycle. The Krebs cycle takes place in the matrix and requires oxygen. Two ATP and 4 CO2 molecules form as the cycle turns twice, once for each pyruvate molecule. NADH2 carries hydrogen atoms from glycolysis and the Krebs cycle to electron carriers (electron transport system) embedded in the cristae. As electrons pass down the system of carriers, energy is released to generate 32 ATP. Altogether aerobic cellular respiration generates 36 ATP. Fermentation When no oxygen is present for pyruvate to enter the Krebs cycle, pyruvate is converted to lactic acid through fermentation, producing few ATP. Lactic acid is toxic to many cells and leads to muscle fatigue. 14 Mader VRL CD-ROM Image 0072l.jpg (Fig. 3.13) Image 0073l.jpg (Fig. 3.14) Image 0074l.jpg (Fig. TA3.3) Image 0075l.jpg (Fig. 3A) Life Science Animations VRL 2.0 Mader ESP Modules Online Case Studies Online Transparencies Image 0076l.jpg (Fig. TA3.4) Cell/Energy and Enzymes/Enzymes are Specific Cell/Energy and Enzymes/How Enzymes Work Cell/Energy and Enzymes/The ATP Cycle Cell/Cell Respiration/Electron Transport Cell/Cell Respiration/Overview of Glycolysis Cell/Cell Respiration/Glycolysis_1 Cell/Cell Respiration/Glycolysis_2 Cell/Cell Respiration/Acetyl-CoA Formation Cell/Cell Respiration/Overview of the Krebs Cycle Cell/Cell Respiration/Krebs Cycle Cell/Cell Respiration/Products of Krebs Cycle Cell/Cell Respiration/Electron Transport Chain in Mitochondria Cell/Cell Respiration/Electron Transport System Cell/Cell Respiration/Transferring Hydrogen Atoms Cell/Cell Respiration/Chemiosmosis Cells/Metabolism/Thermodynamics Cells/Metabolism/Coupled Reactions Cells/Metabolism/Enzymes Cells/Metabolism/Pathways Cells/Respiration/Introduction Cells/Respiration/Glycolysis Cells/Respiration/Transition Cells/Respiration/Krebs Cycle Cells/Respiration/Electron Transport Cells/Respiration/Fermentation Cells/Respiration/Summary Cells/Respiration/Other Nutrients Embryonic Stem cells: The Future of Organ Transplants The Case of Rachel Martin and Lactic Acid 48 (Fig. 3.13) 49 (Fig. 3.14) 50 (Table 3.4) 51 (Fig. TA3.2) SEVENTH EDITION CHANGES New/Revised Text: This was chapter 2 in the previous edition. 3.3 Cellular Metabolism. The discussion of cellular respiration has been simplified. The phrase aerobic cellular respiration has been changed to cellular respiration for clarity. New Bioethical Focus: Stem Cells New/Revised Figures: 3.3 Animal cell; 3.5 Tonicity; 3.7 The nucleus and the nuclear envelope; 3.9 The Golgi apparatus; 3.12 Sperm cells; 3.14 Cellular respiration 15 STUDENT ACTIVITIES Stem Cells and Bioethics 1. Read the Bioethical Focus “Stem Cells”. Explain to students the tragic effects of progressive neurological diseases such as Parkinson disease and how stem cell research using embryos might provide a remedy. Next, discuss the current political administration that rejects the use of embryos in stem cell research. Survey the class for opinions. Why so tiny? 2. Illustrate limits to cell size by giving a group of students 27 wooden blocks (children’s toy blocks). Stack them in a single cube (of 3x3x3 blocks). Use “wb” as units of measurement. So each face of a block has a surface area of 1 wb2, and each block has a volume of 1 wb3. Draw a table on the chalkboard like this, and help the students calculate the surface area-to-volume ratio of three configurations of these 27 blocks. arrangement surface area volume SA/V All in one cube 54 wb2 27 wb3 2 wb2/wb3 3 sheets of 9 blocks 90 wb2 27 wb3 3.33 wb2/wb3 27 individual blocks 162wb2 27 wb3 6 wb2/wb3 This allows students to visualize how smaller cells have a greater surface area-to-volume ratio. Do Onions Make You Cry? 3. Enzymes trigger metabolic reactions in cells. It is also true that cells compartmentalize different compounds, an asset of eukaryotic cells that prokaryotes do not possess. To illustrate both the action of enzymes and of cell compartmentalization, consider the following: Plants, such as onions and garlic, produce compounds aimed at deterring predators. These same compounds are what make onions and garlic so appealing to us as flavorings and food. In onions and garlic, one enzyme is stored between cells, and another compound is stored within cells. When the bulb of either plant is cut, either with a knife or from a grazing predator, the enzyme and the compound mix, producing a chemical reaction that releases a lachrymator--a potent compound that stings human eyes. Tears result when the lachrymator contacts moist eye tissues, producing sulfuric acid. A demonstration of this reaction in the classroom is illustrative. 16