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Transcript
Chapter 4 Functional Anatomy of Prokaryotic and Eukaryotic Cells © 2013 Pearson Education, Inc. Lectures prepared by Christine L. Case Prokaryotic and Eukaryotic Cells • Prokaryote comes from the Greek words for prenucleus. • Eukaryote comes from the Greek words for true nucleus. Prokaryote Eukaryote • One circular chromosome, not in a membrane • No organelles • Bacteria: peptidoglycan cell walls • Archaea: pseudomurein cell walls • Binary fission • Paired chromosomes, in nuclear membrane • Organelles • Polysaccharide cell walls • Mitotic spindle Prokaryotic Cells: Shapes • Average size: 0.2–1.0 µm 2–8 µm • Most bacteria are monomorphic • A few are pleomorphic Figure 4.9b Flagella and bacterial motility. A Proteus cell in the swarming stage may have more than 1000 peritrichous flagella. Basic Shapes • Bacillus (rod-shaped) • Coccus (spherical or circular) • Spiral • Spirillum • Vibrio • Spirochete Figure 4.1a Arrangements of cocci. Plane of division Diplococci Streptococci Figure 4.2ad Bacilli. Single bacillus Coccobacillus Figure 4.4 Spiral bacteria. Vibrio Spirillum Spirochete Bacillus or Bacillus • Scientific name: Bacillus • Shape: bacillus Figure 4.5a Star-shaped and rectangular prokaryotes. Star-shaped bacteria Figure 4.5b Star-shaped and rectangular prokaryotes. Rectangular bacteria Arrangements • Pairs: diplococci, diplobacilli • Clusters: staphylococci • Chains: streptococci, streptobacilli Figure 4.1ad Arrangements of cocci. Plane of division Diplococci Streptococci Staphylococci Figure 4.2b-c Bacilli. Diplobacilli Streptobacilli Figure 4.6 The Structure of a Prokaryotic Cell. Pilus Cell wall The drawing below and the micrograph at right show a bacterium Capsule sectioned lengthwise to reveal the Although the nucleoid appears internal composition. Not all bacteria split in the photomicrograph, have all the structures shown; only the thinness of the “slice” does structures labeled in red are found in not convey theobject’s depth. all bacteria. Cytoplasm 70S Ribosomes Plasma membrane Nucleoid containing DNA Inclusions Plasmid Fimbriae Capsule Cell wall Plasma membrane Flagella . © 2013 Pearson Education, Inc. Glycocalyx • Outside cell wall • Usually sticky • Capsule: neatly organized • Capsules prevent phagocytosis • Hard to get rid of • Slime layer: unorganized and loose • Can be rinsed off with disinfectants • Extracellular polysaccharide allows cell to attach • Important component of biofilms Figure 24.12 Streptococcus pneumoniae, the cause of pneumococcal pneumonia. Flagella • • • • Outside cell wall Made of chains of flagellin Attached to a protein hook Anchored to the wall and membrane by the basal body • Rotate flagella to run or tumble • Move toward or away from stimuli (taxis) Figure 4.8b The structure of a prokaryotic flagellum. Grampositive Flagellum Filament Cell wall Hook Basal body Peptidoglycan Plasma membrane Cytoplasm Parts and attachment of a flagellum of a gram-positive bacterium Figure 4.8a The structure of a prokaryotic flagellum. Flagellum Gramnegative Cell wall Filament Hook Basal body Peptidoglycan Outer membrane Plasma Cytoplasm membrane Parts and attachment of a flagellum of a gram-negative bacterium Figure 4.9a Flagella and bacterial motility. Run Tumble Run Tumble Run Tumble A bacterium running and tumbling. Notice that the direction of flagellar rotation (blue arrows) determines which of these movements occurs. Gray arrows indicate direction of movement of the microbe. Figure 4.7 Arrangements of bacterial flagella. Peritrichous Lophotrichous and polar Monotrichous and polar Amphitrichous and polar Axial Filaments • Also called endoflagella • In spirochetes • Anchored at one end of a cell • Rotation causes cell to move Figure 4.10b Axial filaments. Outer sheath Cell wall Axial filament A diagram of axial filaments wrapping around part of a spirochete (see Figure 11.26a for a cross section of axial filaments) Fimbriae and Pili • Found on many gram NEGATIVE bacteria • Short, thin, hairlike appendages • 2 Types: 1. Fimbriae • Allow attachment which usually leads to infection • Different numbers 2. Pili • Facilitate transfer of DNA from one cell to another • Motility • 1-2 per cell Figure 4.11 Fimbriae. Fimbriae The Cell Wall • Prevents osmotic lysis • Made of peptidoglycan (in bacteria) CELL WALL Differences in Cell Walls GRAM POSITIVE • Thick peptidoglycan • Teichoic acids • May regulate movement of cations • Penicillin sensitive GRAM NEGATIVE Thin peptidoglycan Outer membrane Lipopolysaccharides Protection from phagocytes, complement, and antibiotics Tetracycline Sensitive Figure 4.13b-c Bacterial cell walls. Peptidoglycan Wall teichoic acid Lipoteichoic acid Cell wall Plasma membrane Protein O polysaccharide Core polysaccharide Gram-positive cell wall Core polysaccharide O polysaccharide Lipopolysaccharide Lipid A Cell wall Gram-negative cell wall Lipid A Parts of the LPS Porin protein Lipoprotein Outer membrane Phospholipid Peptidoglycan Plasma membrane Periplasm Protein The Gram Stain Mechanism • Crystal violet-iodine crystals form in cell • Gram-positive • Alcohol dehydrates peptidoglycan • CV-I crystals do not leave • Gram-negative • Alcohol dissolves outer membrane and leaves holes in peptidoglycan • CV-I washes out Table 4.1 Some Comparative Characteristics of Gram-Positive and Gram-Negative Bacteria Atypical Cell Walls • Acid-fast cell walls • Like gram-positive cell walls • Waxy lipid (mycolic acid) bound to peptidoglycan • 2 Genera: • Mycobacterium • Nocardia Figure 24.8 Mycobacterium tuberculosis. Atypical Cell Walls • Mycoplasmas • Lack cell walls • Sterols in plasma membrane • Archaea • Wall-less • Walls without peptidoglycan Damage to the Cell Wall • • • • Lysozyme- enzyme that digests peptidoglycan Penicillin- inhibits peptide bridges in peptidoglycan Protoplast- wall-less cell gram-positive cell Spheroplast- wall-less gram-negative cell • Protoplasts and spheroplasts are susceptible to osmotic lysis • L forms-wall-less cells that swell into irregular shapes Figure 4.14a Plasma membrane. Lipid bilayer of plasma membrane Peptidoglycan Outer membrane Plasma membrane of cell The Plasma Membrane • Selectively permeable • Produce ATP • Damage to the membrane by alcohols, ammonium (detergents), and polymyxin antibiotics causes leakage of cell contents • Phospholipid bilayer • Proteins: 1. Peripheral proteins- inner or outer surface • Act as enzymes • Support • Changes in shape during movement 2. Integral proteins (transmembrane)-penetrate membrane completely • Channels or pores through which substance leave and enter the cell Figure 4.14b Plasma membrane. Outside Lipid bilayer Pore Peripheral protein Inside Polar head Nonpolar fatty acid tails Polar head Lipid bilayer of plasma membrane Integral proteins Peripheral protein Movement of Materials across Membranes • Simple diffusion: movement of a solute from an area of high concentration to an area of low concentration Movement of Materials across Membranes • Facilitated diffusion: solute combines with a transporter protein in the membrane Movement of Materials across Membranes • Osmosis: the movement of water across a selectively permeable membrane from an area of high water to an area of lower water concentration Movement of Materials across Membranes • Through lipid layer • Aquaporins (water channels) Figure 4.18c-e The principle of osmosis. Cytoplasm Solute Plasma membrane Water Isotonic solution. No net movement of water occurs. Hypotonic solution. Water moves into the cell. If the cell wall is strong, it contains the swelling. If the cell wall is weak or damaged, the cell bursts (osmotic lysis). Hypertonic solution. Water moves out of the cell, causing its cytoplasm to shrink (plasmolysis). Movement of Materials across Membranes • Active transport: requires a transporter protein and ATP • Group translocation: requires a transporter protein and the substance going across the protein is CHEMICALLY changed Cytoplasm • The substance inside the plasma membrane • Contains 80% water • Contains major structures of the cell Genetic Information • Bacterial chromosomegenetic information for the cell’s structure and function;usually circular • Plasmidextrachromosomal genetic information; may carry genes for antibiotic resistance, tolerance to metals, toxin production The Prokaryotic Ribosome • Protein synthesis • 70S • 50S + 30S subunits Inclusions Reserve deposits Store nutrients to have in times of need. © 2013 Pearson Education, Inc. Endospores • • • • • Resting cells Resistant to desiccation, heat, chemicals Bacillus, Clostridium Sporulation: endospore formation Germination: return to vegetative state Figure 4.21b Formation of endospores by sporulation. Endospore An endospore of Bacillus subtilis Figure 4.21a Formation of endospores by sporulation. Cell wall Cytoplasm Spore septum begins to isolate newly replicated DNA and a small portion of cytoplasm. Plasma membrane starts to surround DNA, cytoplasm, and membrane isolated in step 1. Plasma membrane Bacterial chromosome (DNA) Sporulation, the process of endospore formation Spore septum surrounds isolated portion, forming forespore. Two membranes Peptidoglycan layer forms between membranes. Endospore is freed from cell. Spore coat forms. Figure 4.22a Eukaryotic cells showing typical structures. PLANT CELL ANIMAL CELL Peroxisome Flagellum Mitochondrion Microfilament Golgi complex Microtubule Vacuole Chloroplast Ribosome Cytoplasm Smooth endoplasmic reticulum Cell wall Nucleus Nucleolus Golgi complex Basal body Cytoplasm Microfilament Lysosome Centrosome: Centriole Pericentriolar material Ribosome Microtubule Nucleus Nucleolus Plasma membrane Highly schematic diagram of a composite eukaryotic cell, half plant and half animal Peroxisome Rough endoplasmic reticulum Mitochondrion Smooth endoplasmic reticulum Plasma membrane Figure 4.23a-b Eukaryotic flagella and cilia. Flagellum Cilia A micrograph of Euglena, a chlorophyllcontaining alga, with its flagellum. A micrograph of Tetrahymena, a common freshwater protozoan, with cilia. Flagella and Cilia • Microtubules- long hollow tubes • 9 pairs + 2 arrangement • Flagella- move in a wavelike manner. The Cell Wall and Glycocalyx • Cell wall • Plants, algae, fungi • Cellulose (Plants) • Chitin (Fungi) • Glucan and Mannan (Yeasts) • Glycocalyx • Carbohydrates extending from plasma membrane • Strengthens cell surface, attachment of cells together, cell-cell recognition The Plasma Membrane • • • • • Phospholipid bilayer Peripheral proteins Integral proteins Transmembrane proteins Sterols- important in cells without cell wall because it offers stability to the cell • Glycocalyx carbohydrates The Plasma Membrane • • • • • • Selective permeability allows passage of some molecules Simple diffusion Facilitative diffusion Osmosis Active transport Endocytosis • Phagocytosis: pseudopods extend and engulf particles • Pinocytosis: membrane folds inward, bringing in fluid and dissolved substances Table 4.2 Principal Differences between Prokaryotic and Eukaryotic Cells Cytoplasm • Cytosol: fluid portion of cytoplasm • Cytoskeleton: microfilaments, intermediate filaments, microtubules • Provides support and shape and assists in transportation of substances. • Cytoplasmic streaming: movement of cytoplasm throughout cells Ribosomes • Protein synthesis • 80S • Membrane-bound: attached to ER • Free: in cytoplasm • 70S • In chloroplasts and mitochondria Organelles • Nucleus: contains chromosomes • The control center • Most prominent internal organelle. • Composed of: • Nuclear envelope- 2 parallel membranes that are separated by a space; also has small pores on the surface • Nucleoplasm- inside space of the nucleus • Nucleolus- granular mass; RNA synthesis and ribosomal subunit collection area • Lysosome: digestive enzymes • Vacuole: brings food into cells and provides support Figure 4.24c The eukaryotic nucleus. Nuclear pore(s) Nuclear envelope Nucleolus Chromatin Endoplasmic Reticulum • • • • • Microscopic tunnel system made of cisternae Functions: Storage Transportation 2 types: • Rough endoplasmic reticulum (RER)- continuous with the nuclear envelope; has ribosomes on surface; transports materials from nucleus to the cytoplasm and is responsible for protein synthesis. • Smooth endoplasmic reticulum (SER)- continuous with RER; no ribosomes; is responsible for nutrient processing and synthesis and storage of lipids, electrolytes, and other substances. Figure 4.25 Rough endoplasmic reticulum and ribosomes. Nuclear envelope Ribosomes Cisternae Smooth ER Ribosomes Rough ER Golgi Complex • Modify and secrete proteins • 3 types of vesicles: 1. 2. 3. Transitional- membrane bound packets of proteins that come to the Golgi from the ER for modification. Condensing- membrane bound packets of proteins that pinch off from the Golgi and are used by organelles on the inside of the cell Secretory-membrane bound packets of proteins that pinch off from the Golgi and are transported outside of the cell Figure 4.26 Golgi complex. Secretory vesicles Transfer vesicles Cisternae Transport vesicle from rough ER • Lysosomes • Contain digestive enzymes capable of breaking down substances • Vacuoles • Temporary storage units • Help to bring food into cell • Take in water Figure 4.22b Eukaryotic cells showing typical structures. Peroxisome Nucleus Vacuole Animal cell, an antibody-secreting plasma cell Chloroplast Golgi complex Mitochondrion Plasma membrane Nucleus Cytoplasm Nucleolus Cell wall Algal cell (Tribonema vulgare) Transmission electron micrographs of plant and animal cells. Mitochondrion Rough endoplasmic reticulum Lysosome Mitochondria • “Powerhouse” of the cell • Supplies most of the energy for the cell • Number varies • Carries out cellular respiration and produces ATP. Chloroplasts • Algae • Helps with photosynthesis Peroxisomes • Similar to lysosomes. • Store enzymes • Catalase- breaks down hydrogen peroxide (H2O2) Centrosome • Composed of protein fibers and centrioles • Plays critical role in cellular division • Makes microtubles Figure 10.2 A model of the origin of eukaryotes. Endosymbiotic Theory • What are the fine extensions on the protozoan shown on the following slide? • Larger bacteria engulfed smaller bacteria. Their relationship became symbiotic.