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Transcript
9/1/2016 Chapter 3: Cellular Structure 1. Prokaryotic Cell Structure 2. Eukaryotic Cell Structure 1. Prokaryotic Cell Structure A. Cell Shape B. External Structures C. Internal (Cytoplasmic) Structures A. Cell Shape Chapter Reading – pp. 322-325 1 9/1/2016 Prokaryotic Cell Shape One convenient characteristic with which to identify and classify prokaryotes is their size and shape as seen in the microscope. • the diameter of prokaryotic cells ranges from ~0.2 to 2.0 mm • prokaryotes are essentially unicellular and more or less maintain a constant shape (monomorphic) • most prokaryotes have a spherical, rod-shaped or spiral appearance though other shapes exist as well… Spherical Cells • spherical prokaryotes are referred to as cocci (singular = coccus) • different kinds of cocci exhibit characteristic arrangements: diplo- = found in pairs strepto- = found in chains staphylo- = irregular clusters tetrad = group of 4 sarcina = cube structure of 8 “Rod-Shaped” Cells • rod-shaped prokaryotes are referred to as bacilli (singular = bacillus) • also found in various arrangements: diplo- = length-wise pairs strepto- = length-wise chains” cocco- = “rounded” bacilli palisade = bacilli “side by side” 2 9/1/2016 Curved or Spiral Cells vibrio = “curved rod” spirillum = “twisted rod” spirochete = “corkscrew rod” B. External Structures Chapter Reading – pp. 59-71 Prokaryotic Cell Structures Inclusions Ribosome Cytoplasm Flagellum Nucleoid Glycocalyx Cell wall Cell membrane 3 9/1/2016 Plasma Membrane Head, which contains phosphate (hydrophilic) true barrier between “internal” & “external” Phospholipid Tail (hydrophobic) Integral proteins Cytoplasm Phospholipid bilayer Integral glycoprotein Integral protein Peripheral protein • phospholipid content is a bit different compared to eukaryotes Diffusion & Osmosis Extracellular fluid Cytoplasm Diffusion through the phospholipid bilayer Facilitated diffusion through a nonspecific channel protein Facilitated diffusion through a permease specific for one chemical; binding of substrate causes shape change in channel protein Osmosis, the diffusion of water through a specific channel protein or through a phospholipid bilayer Concentration Gradients Na+ Cl – Cell exterior (extracellular fluid) Different concentrations of ions inside vs outside the cell are set up & maintained by : Cytoplasmic membrane Integral protein Protein DNA Protein Cell interior (cytoplasm) • protein pumps • active transport from low to high conc. • protein channels & transport proteins • facilitated diffusion Creates a net negative charge inside vs outside. 4 9/1/2016 Bacterial Cell Wall The bacterial cell wall provides structure & support: • main component is a structure called peptidoglycan • polypeptide-linked chains of a repeating disaccharide repeating disaccharide backbone Glucose tetrapeptide (amino acid) crossbridge N-acetylglucosamine N-acetylmuramic acid NAG NAM (protects cell from osmotic lysis!) connecting chains of amino acids Osmosis & Cell Lysis Cells without a wall (e.g., mycoplasmas, animal cells) H 2O H2O H2O Cells with a wall (e.g., plants, fungal and bacterial cells) Cell wall Cell wall H2O H2O Cell membrane H2O Cell membrane Isotonic solution Hypertonic solution Hypotonic solution Porin Outer membrane of cell wall Porin (sectioned) Peptidoglycan layer of cell wall Periplasmic space Cell membrane n O side chain (varies in length and composition) Lipopolysaccharide (LPS) Phospholipid layers Integral proteins Gram-negative Cell Wall Core polysaccharide Lipid A (embedded in outer membrane) Gram-negative cell wall • thin layer of peptidoglycan Fatty acid • outer membrane containing lipopolysaccharide (LPS) • Lipid A (endotoxin) + polysaccharide 5 9/1/2016 Gram-positive Cell Wall Peptidoglycan layer (cell wall) Cell membrane Lipoteichoic acid Teichoic acid Integral protein Gram-positive cell wall • thick-layered peptidoglycan cell wall w/teichoic acids • NO outer membrane Bacterial Glycocalyx (“sugar cup”) Outermost layer that surrounds the bacterium • called a capsule if compact, tightly attached to cell wall • called a slime layer if loosely attached, water soluble • mediates adhesion, biofilm formation • protects from dessication, phagocytosis Bacterial Flagellum • basal body, hook & filament • basal body anchors flagellum in PM, cell wall, rotates hook & filament to propel bacterium 6 9/1/2016 Flagella & Bacterial Motility Bacteria undergo taxis, i.e. movement in response to something. e.g., chemotaxis (movement in response to a chemical substance) Tumble Run attractant (RUN = flagella rotate counterclockwise) Run Tumble (TUMBLE = clockwise) Involves random “runs” & “tumbles”: • longer runs, less tumbles in direction of “good stuff” Axial Filament Bundle of endoflagella found in spirochetes • anchored at one end of cell and rotate in unison • rotates cell like a “corkscrew” to propel it forward Fimbriae & Pili Non-motile appendages that are chemically and functionally different than flagella. Pili (singular = pilus) Fimbriae • involved in adhesion Fimbria Flagellum • used in conjugation Conjugation pilus 7 9/1/2016 C. Internal (Cytoplasmic) Structures Chapter Reading – pp. 71-76 Prokaryotic Ribosomes Carry out protein synthesis (i.e., translation of mRNA). Ribosomes consist of 1 large and 1 small subunit. • both subunits are made of rRNA & ribosomal proteins • smaller, somewhat different from eukaryotic ribosomes • specifically targeted by some antibiotics Endospores Cell wall Cytoplasmic membrane 1 DNA is replicated. DNA Vegetative cell 2 DNA aligns along the cell’s long axis. When conditions are bad, some Gram+ bacteria can form endospores: • inactive, dormant cells enclosed in a highly resistant spore coat 3 Cytoplasmic membrane invaginates to form forespore. Forespore 4 Cytoplasmic membrane grows and engulfs forespore within a second membrane. Vegetative cell’s DNA disintegrates. First membrane Second membrane • remain dormant until conditions are good (even 1000’s of yrs!) • very resistant to heating, freezing, dessication 8 9/1/2016 Completion of Endospore Formation 5 A cortex of calcium and dipicolinic acid is deposited between the membranes. 6 Spore coat forms around endospore. Cortex Spore coat Outer spore cost 7 Maturation of endospore; completion of spore coat and increase in resistance to heat and chemicals by unknown process. 8 Endospore released from original cell. Endospore Outer spore cost The Genetic Material A region called the nucleoid contains the circular bacterial chromosome (DNA + non-histone proteins): • usually several million base pairs (bp) in size e.g. the E. coli genome is ~4 mega-bp’s (4 Mbp) • contains all bacterial genes plus an origin of replication (Ori) • Ori is where DNA replication starts, essential to copy the chromosome Plasmids Some bacteria have >1 extrachromosomal, non-essential circular DNA molecules called plasmids: plasmid map • much smaller than bacterial chromosome • several kilo-base pairs (usu. 3-6 Kb) • have own Ori so it is copied when cell divides 9 9/1/2016 What’s the Role of Plasmids? Plasmids generally contain genes that confer some sort of advantage for survival and reproduction: 1) genes providing protection from toxic substances • including antibiotic resistance 2) genes enabling the metabolism of additional sources of energy 3) genes for toxins to kill microbial competitors, enhance pathogenicity 4) genes involved in gene transfer by conjugation Inclusions & Chromatophores Inclusions are deposits of various materials found in certain types of bacteria (e.g., magnetosomes). Chromatophores are pigment-containing infoldings of the plasma membrane in some photosynthetic bacteria. 2. Eukaryotic Cell Structure Chapter Reading – pp. 77-86 10 9/1/2016 Eukaryotic Organelles Nuclear envelope Nuclear pore Lysosome Mitochondrion Nucleolus Centriole Perinuclear space Secretory vesicle Cilia Golgi body Transport vesicles Ribosomes Rough endoplasmic reticulum Cell membrane Cytoskeleton Smooth endoplasmic reticulum Nucleus Storage of Genetic Material: • DNA + histones = Nucleolus Nucleoplasm Chromatin Nuclear envelope Chromosomes when condensed in M phase Chromatin when uncondensed Two phospholipid bilayers Nuclear pores Rough ER Nucleolus • assembly of ribosomes from rRNA & proteins Rough ER Endoplasmic Reticulum (ER) Rough ER (RER) • ribosomes on cytoplasmic face of ER membrane synthesize proteins across ER membrane into lumen Membrane-bound • beginning of the secretory pathway Smooth ER (SER) ribosomes Mitochondrion Free ribosomes • no ribosomes • has membraneassociated enzymes that catalyze new lipid synthesis (also found in RER) Smooth endoplasmic reticulum (SER) Rough endoplasmic reticulum (RER) 11 9/1/2016 The Golgi Complex Proteins destined to leave ER next go to the Golgi • transported in vesicles, next stop in “secretory pathway” Secretory vesicles • undergo any necessary modifications or processing • then sent via vesicles to various destinations • e.g., plasma membrane, exterior of cell, other organelles Vesicles arriving from ER Mitochondrion ATP production via cellular respiration • Krebs cycle • e- transport • chemiosmosis Outer membrane • high [H+] in the intermembrane space due to e- transport in inner membr. Inner membrane Crista *H+ gradient fuels ATP synthesis* Matrix Ribosomes Chloroplast Organelle of photosynthesis: • “light” reactions occur in the thylakoids Granum • convert sunlight to energy in ATP and NADPH • “dark” reactions occur in stroma • energy from ATP & NADPH used to make sugars from CO2 and H2O Stroma Thylakoid Inner bilayer membrane Outer bilayer membrane 12 9/1/2016 Flagella & Cilia Microbial structures used for locomotion: Flagella • long & “few” • wave-like motion Cilia • short & “many” Other Organelles Lysosomes • acidic compartments for the breakdown or “digestion” of foreign or waste material Vacuoles • large storage compartments Peroxisomes • metabolize fats for heat production, degrade toxins • H2O2 byproduct is “neutralized” by catalase Centrosomes • region containing centrioles and other proteins • “organizing center” for mitotic spindle fibers Key Terms for Chapter 3 • coccus, bacillus, vibrio, spirillum, spirochete • diplo-, strepto-, staphylo-, tetrad, sarcina • peptidoglycan, teichoic acid, LPS, endotoxin • glycocalyx, capsule, fimbriae, pili • chemotaxis, endospores, plasmids, nucleoid • inclusions, chromatophores, vegetative • periplasmic space (periplasm) Relevant Chapter Questions MC: 1, 5, 7-10, 13-15 Matching: 1, 2 Labeling (both) SA: 1-4, 7-10, 12-16 13