Tortora Chapter 04

PowerPoint PresentationMicrobiology
AN INTRODUCTION
EIGHTH EDITION
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Prokaryotic Cells
Prokaryote comes from the Greek words for prenucleus.
Eukaryote comes from the Greek words for true nucleus.
Learning objective: compare and contrast overall cell structure of prokaryotes and eukaryotes.
Prokaryote Eukaryote
Cell membrane
No histones
No organelles
Histones
Organelles
Average size: 0.2 -1.0 µm 2 - 8 µm (1 x 10-6 m)
Are unicellular and most multiply by binary fission
Basic shapes:
COCCUS BACILLUS SPIRAL
Arrangements
Arrangements of cocci:
Arrangements of bacilli:
Arrangements of spiral bacteria:
Double-stranded helix formed by Bacillus subtilis.
Bacillus cells often remain attached to each other, forming extended chains.
Unusual shapes (Prokaryotes)
Most bacteria are monomorphic (single shape)
A few are pleomorphic (many shapes)
Figure 4.5
Learning objective: Describe the structure and function of the glycocalyx, flagella, axial filaments, fimbriae, and pili.
Prokaryote cell
Glycocalyx
A slime layer is unorganized & loose glycocalyx
Extracellular polysaccharide (EPS) allows cell to attach
Capsules prevent phagocytosis
Figure 4.6a, b
Flagella
Long filamentous appendages of a filament, hook, and basal body
Outside cell wall
Anchored to the wall and membrane by the basal body
Figure 4.8
Flagella Arrangement
Figure 4.7
Motile Cells
Move toward or away from stimuli (positive and negative taxis)
Flagella H proteins are antigens
(e.g., E. coli O157:H7)
Motile Cells
Figure 4.9
A Proteus cell swarming may have 1000+ peritrichous flagella. (from all sides)
Axial Filaments (endoflagellum)
Rotation causes cell to move
Figure 4.10a
Fimbriae and Pili
Are short, thin appendages
Fimbriae of this E. Coli cell allow attachment (velcro). Cell is beginning to divide.
Pili are used to transfer DNA from one cell to another
Figure 4.11
Cell Wall
Prevents osmotic lysis (protects against changes in water pressure)
Made of peptidoglycan (in bacteria = NAG+NAM+amino acids) – penicillin interferes with production of peptidoglycan
Contributes to disease capability and site of action of some antibiotics.
Figure 4.6a, b
Differentiate between protoplast, spheroplast, and L form.
Peptidoglycan (murein)
Linked by polypeptides
The small arrows denote where penicillin interferes with linkage of peptidoglycan rows.
Gram positive vs. gram negative cell walls
Figure 4.13b, c
Gram-positive cell walls Gram-negative cell walls
Thick peptidoglycan
Teichoic acids (alcohol+phosphate)
In acid-fast cells, contains mycolic acid (waxy lipid) – allows them to be grouped into medically significant types.
Thin peptidoglycan (subject to mechanical breakage)
No teichoic acids
Gram-Positive cell walls
Polysaccharides provide antigenic variation (identification)
Figure 4.13b
Gram-Negative Outer Membrane
Lipopolysaccharides, lipoproteins, phospholipids.
Forms the periplasm between the outer membrane and the plasma membrane.
Protection from phagocytes, complement (30+ liver proteins that protect host), antibiotics.
O polysaccharide antigen, e.g., E. coli O157:H7.
Lipid A is an endotoxin.
Porins (proteins) form channels through membrane to pass other molecules
Gram-Negative Outer Membrane
Gram Stain Mechanism
Crystal violet-iodine (CV-I) crystals form in cell combining with peptidoglycan
Gram-positive
Gram-negative
CV-I washes out
Atypical Cell Walls
Walls of pseudomurein (lack NAM and D amino acids, peptidoglycan)
Damage to Cell Walls
Lysozyme digests disaccharide in peptidoglycan (gram+ cell walls destroyed, gram- damaged, resulting in spheroplast).
Spheroplast is a wall-less Gram-positive cell.
Penicillin inhibits peptide bridges in peptidoglycan.
Protoplast is a wall-less cell.
L forms are wall-less cells that swell into irregular shapes (gram+ and -).
Protoplasts and spheroplasts are susceptible to osmotic lysis.
Plasma (cytoplasmic) Membrane
Plasma Membrane – Fluid Mosaic Model
Selectively permeable
Phospholipid bilayer
Peripheral proteins
Integral proteins
Transmembrane proteins
Figure 4.14b
Fluid Mosaic Model
Proteins move to function
Figure 4.14b
Plasma Membrane
Selective permeability allows passage of some molecules
Enzymes for ATP production
Damage to the membrane by alcohols, quaternary ammonium (detergents) and polymyxin antibiotics causes leakage of cell contents.
Movement Across Membranes
Movement may be passive (no energy expenditure – diffusion or facilitated diffusion):
Simple diffusion: Movement of a solute from an area of high concentration to an area of low concentration. (ions move until equilibrium reached)
Facilitative diffusion: Solute combines with a transporter protein in the membrane.
Osmosis (always involves water):
Movement of water across a selectively permeable membrane from an area of high water concentration to an area of lower water.
Osmotic pressure
The pressure needed to stop the movement of water across the membrane.
Figure 4.18a
Osmosis
Low to high concentration (against gradient) – cell must expend energy:
Active transport of substances requires a transporter protein and ATP.
Group translocation of substances requires a transporter protein and PEP. (phospheonolpyruvic acid)
Cytoplasm
Cytoplasm is the fluid substance inside the plasma membrane (water, inorganic and organic molecules, DNA, ribosomes, and inclusions)
Figure 4.6a, b
Nuclear Area
Bacteria can contain plasmids – circular DNA
Figure 4.6a, b
Learning objectives: Identify functions of the nuclear area, ribosomes, and inclusions.
Ribosomes = rRNA + proteins
Figure 4.6a
Sites of protein synthesis (rRNA) – free floating, not tied to endoplasmic reticulum as in eukaryotes.
Ribosomes
Figure 4.19
The letter S refers to Svedberg units = relative rate of sedimentation.
Because of differences in prokaryotic and eukaryotic ribosomes, the microbe can be killed by antibiotics while eukaryotic host cell is unaffected.
Inclusions
Protein covered cylinders
Iron-oxide inclusions in some gram-negative bacteria that act like magnets.
Endospores
Sporulation: Endospore formation
Bacillus, Clostridium
Learning objective: Describe the functions of endospores, sporulation, and endospore germination.
Endospores tend to form under conditions of stress.
Eukaryotic Cells
Prokaryote comes from the Greek words for prenucleus.
Eukaryote comes from the Greek words for true nucleus.
Eukaryotic Flagella and Cilia
Flagella and Cilia
Flagella are few and long (motility), cilia are numerous and short (motility and move substances along cell surface)
Microtubules
Tubulin
Cell Wall and Glycocalyx
Carbohydrates
Glycocalyx surround animal cells (strength, attachment to other cells)
Carbohydrates extending from animal plasma membrane
Bonded to proteins and lipids in membrane
Learning objective: Compare and contrast prokaryotic and eukaryotic cell walls and glycocalyxes.
Plasma Membrane
Peripheral proteins
Integral proteins
Transmembrane proteins
Glycocalyx carbohydrates not found in p. cells except Mycoplasma bacteria
Learning objective: Compare and contrast prokaryotic and eukaryotic plasma membranes.
Plasma Membrane
Simple diffusion
Facilitative diffusion
Pinocytosis: Membrane folds inward bringing in fluid and dissolved substances (liquids)
Eukaryotic Cell
Cytosol Fluid portion of cytoplasm
Cytoskeleton Microfilaments, intermediate filaments, microtubules
Cytoplasmic streaming Movement of cytoplasm throughout cells
Learning objectives:
Define organelle.
Organelles
Nucleus Contains chromosomes (DNA)
ER Transport network, ribosomes
Lysosome Digestive enzymes
Mitochondrion Cellular respiration (ATP)
Chloroplast Photosynthesis (70S ribosomes)
destroys H2O2
Eukaryotic Cell
Not membrane-bound:
Centriole Mitotic spindle formation
Eukaryotic Nucleus
Figure 4.24
Endoplasmic Reticulum
Figure 4.25
Smooth ER performs various functions:
Synthesizes phospholipids, fats, steroids
Creates vesicles
Ribosomes
80S
Golgi Complex
Figure 4.26
Golgi complex modifies, sorts, and packages proteins received from the ER; discharges proteins via exocytosis; replaces portions of the plasma membrane; and forms lysosomes (digestive enzymes).
Lysosomes (digestive enzymes)
Vacuoles (storage of toxins, food, water)
Figure 4.22b
Mitochondrion (furnace of the cell)
Figure 4.27
Site of the Krebs Cycle, which produces the energy currency of the cell - ATP
Chloroplast
C6H12O6 + O2 = H2O + CO2 + ATP
Photosynthesis:
Endosymbiotic Theory
Figure 10.2
Learning objective:
Discuss evidence that supports the endosymbiotic theory of eukaryotic evolution.
Mitochondria and chloroplasts resemble bacteria in size and shape as do their ribosomes

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