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PowerPoint® Lecture Presentations prepared by Bradley W. Christian, McLennan Community College
C H A P T E R
© 2016 Pearson Education, Inc.
Functional Anatomy of Prokaryotic and Eukaryotic Cells
4
© 2016 Pearson Education, Inc.
© 2016 Pearson Education, Inc.
Comparing Prokaryotic and Eukaryotic Cells: An Overview
• Prokaryote comes from the Greek words for prenucleus.
• Eukaryote comes from the Greek words for true nucleus.
© 2016 Pearson Education, Inc.
Comparing Prokaryotic and Eukaryotic Cells: An Overview
Prokaryote • One circular chromosome,
not in a membrane • No histones • No organelles • Bacteria: peptidoglycan
cell walls • Archaea: pseudomurein
cell walls • Divides by binary fission
Eukaryote • Paired chromosomes,
in nuclear membrane • Histones • Organelles • Polysaccharide cell walls,
when present • Divides by mitosis
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The Size, Shape, and Arrangement of Bacterial Cells
• Average size: 0.2 to 2.0 µm diameter × 2 to 8 µm length
• Most bacteria are monomorphic (single shape) • A few are pleomorphic (many shapes)
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The Size, Shape, and Arrangement of Bacterial Cells
• Bacillus (rod-shaped) • Coccus (spherical) • Spiral
• Vibrio • Spirillum • Spirochete
• Star-shaped • Rectangular
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Figure 4.4 Spiral bacteria.
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Figure 4.5a Star-shaped and rectangular prokaryotes.
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Figure 4.5b Star-shaped and rectangular prokaryotes.
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The Size, Shape, and Arrangement of Bacterial Cells
• Pairs: diplococci, diplobacilli • Clusters: staphylococci • Chains: streptococci, streptobacilli • Groups of four: tetrads • Cubelike groups of eight: sarcinae
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Plane of division
Diplococci
Streptococci
Tetrad
Sarcinae
Staphylococci
Figure 4.1 Arrangements of cocci.
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Figure 4.2a-d Bacilli.
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Figure 4.2b-c Bacilli.
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The Size, Shape, and Arrangement of Bacterial Cells
• Scientific name: Bacillus • Shape: bacillus
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Figure 4.3 Gram-stained Bacillus anthracis.
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Figure 4.6 The Structure of a Prokaryotic Cell.
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Glycocalyx
• External to the cell wall • Viscous and gelatinous • Made of polysaccharide and/or polypeptide • Two types
• Capsule: neatly organized and firmly attached • Slime layer: unorganized and loose
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Glycocalyx
• Contribute to virulence • Capsules prevent phagocytosis • Extracellular polymeric substance helps form biofilms
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Figure 24.11 Streptococcus pneumoniae, the cause of pneumococcal pneumonia.
Capsules
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Flagella
• Filamentous appendages external of the cell • Propel bacteria • Made of protein flagellin
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Flagella
• Three parts: • Filament: outermost region • Hook: attaches to the filament • Basal body: consists of rod and pairs of rings; anchors
flagellum to the cell wall and membrane
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Gram- positive
Cell wall
Filament
Hook Basal body Peptidoglycan
Plasma membrane
Cytoplasm Parts and attachment of a flagellum of a gram-positive bacterium
Flagellum
Figure 4.8b The structure of a prokaryotic flagellum.
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Flagellum Filament Gram-
negative
Hook Basal body Peptidoglycan Outer membrane
Cell wall
Plasma membrane
Cytoplasm Parts and attachment of a flagellum of a gram-negative bacterium
Figure 4.8a The structure of a prokaryotic flagellum.
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Figure 4.7 Arrangements of bacterial flagella.
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Flagella
• Flagella allow bacteria to move toward or away from stimuli (taxis)
• Flagella rotate to "run" or "tumble" • Flagella proteins are H antigens and distinguish
among serovars (e.g., Escherichia coli O157:H7)
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Figure 4.9a Flagella and bacterial motility.
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Figure 4.9b Flagella and bacterial motility.
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Axial Filaments
• Also called endoflagella • Found in spirochetes • Anchored at one end of a cell • Rotation causes cell to move like a corkscrew
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A photomicrograph of the spirochete Leptospira, showing an axial filament
Axial filament
Figure 4.10a Axial filaments.
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Axial filament Cell wall Outer sheath
A diagram of axial filaments wrapping around part of a spirochete
Figure 4.10b Axial filaments.
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Fimbriae and Pili
• Fimbriae • Hairlike appendages that allow for attachment
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Figure 4.11 Fimbriae.
Fimbriae
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The Cell Wall
• Prevents osmotic lysis and protects the cell membrane
• Made of peptidoglycan (in bacteria) • Contributes to pathogenicity
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Capsule Cell wall
Inclusions
Cytoplasm
70S Ribosomes
Plasma membrane
Cell wall
Nucleoid containing DNA
Capsule
Figure 4.6 The Structure of a Prokaryotic Cell.
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Composition and Characteristics
• Peptidoglycan (backbone) • Polymer of a repeating disaccharide in rows:
• N-acetylglucosamine (NAG) • N-acetylmuramic acid (NAM)
• Rows are linked by polypeptides
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Figure 4.12 N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) joined as in a peptidoglycan.
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NAG
.
N-acetylglucosamine (NAG)
N-acetylmuramic acid (NAM)
Side-chain amino acid
Cross-bridge amino acid
NAM NAG
NAG Peptide bond
Structure of peptidoglycan in gram-positive bacteria
Carbohydrate "backbone"
Peptide cross-bridge
Tetrapeptide side chain
Figure 4.13a Bacterial cell walls.
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Gram-Positive Cell Walls
• Thick peptidoglycan • Teichoic acids
• Thin peptidoglycan • Outer membrane • Periplasmic space
Gram-Negative Cell Walls
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Gram-Positive Cell Walls
• Teichoic acids • Lipoteichoic acid links cell wall to plasma membrane • Wall teichoic acid links the peptidoglycan • Carry a negative charge • Regulate movement of cations (Na +, K+, Ca+)
• Polysaccharides and teichoic acids provide antigenic specificity
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Granular layer
Lipoteichoic acid
Peptidoglycan Wall teichoic acid
Cell wall
Plasma membrane
Protein
Figure 4.13b Bacterial cell walls.
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Gram-Negative Cell Walls
• Periplasm between the outer membrane and the plasma membrane contains peptidoglycan
• Outer membrane made of polysaccharides, lipoproteins, and phospholipids
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Gram-Negative Cell Walls
• Protect from phagocytes and antibiotics • Made of lipopolysaccharide (LPS)
• O polysaccharide functions as antigen (e.g., E. coli O157:H7)
• Lipid A is an endotoxin embedded in the top layer • Porins (proteins) form channels through
membrane
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Periplasm
Peptidoglycan Cell wall
Lipopolysaccharide Lipid A
Protein
Porin protein Lipoprotein
Phospholipid Outer membrane
Plasma membrane
Lipid A (endotoxin)
Core polysaccharide
O polysaccharide (antigenic)
Parts of the LPS
Core polysaccharide O polysaccharide
Figure 4.13c Bacterial cell walls.
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Cell Walls and the Gram Stain Mechanism
• Crystal violet-iodine crystals form inside 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; cells are colorless • Safranin added to stain cells
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Table 4.1 Some Comparative Characteristics of Gram-Positive and Gram-Negative Bacteria
Gram-Positive Gram-Negative
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• 4-rings in basal body of flagella
• Produce endotoxins and exotoxins
• Low susceptibility to penicillin
Gram-Positive Cell Walls
• 2-rings in basal body of flagella
• Produce exotoxins • High susceptibility to
penicillin • Disrupted by lysozyme
Gram-Negative Cell Walls
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Atypical Cell Walls
• Acid-fast cell walls • Like gram-positive cell walls • Waxy lipid (mycolic acid) bound to peptidoglycan • Mycobacterium tuberculosis • Nocardia • Stain with carbolfuchsin
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Figure 24.7 Mycobacterium tuberculosis.
Corded growth
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Atypical Cell Walls
• Mycoplasmas • Lack cell walls • Sterols in plasma membrane
• Archaea • Wall-less, or • Walls of pseudomurein (lack NAM and D-amino acids)
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Damage to the Cell Wall
• Lysozyme hydrolyzes bonds in peptidoglycan • Penicillin inhibits peptide bridges in peptidoglycan • Protoplast is a wall-less gram-positive cell • Spheroplast is a wall-less gram-negative cell
• Protoplasts and spheroplasts are susceptible to osmotic lysis
• L forms are wall-less cells that swell into irregular shapes
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The Plasma (Cytoplasmic) Membrane
• Phospholipid bilayer that encloses the cytoplasm • Peripheral proteins on the membrane surface • Integral and transmembrane proteins penetrate
the membrane
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Lipid bilayer of plasma membrane Peptidoglycan Outer membrane
Plasma membrane of cell
Figure 4.14a Plasma membrane.
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Outside
Pore Peripheral protein
Polar head
Nonpolar fatty acid tails Polar head
Peripheral protein
Integral proteins
Inside
Lipid bilayer
Lipid bilayer of plasma membrane
Figure 4.14b Plasma membrane.
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Structure
• Fluid mosaic model • Membrane is as viscous as olive oil • Proteins move freely for various functions • Phospholipids rotate and move laterally • Self-sealing
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Functions
• The plasma membrane's selective permeability allows the passage of some molecules, but not others • Large molecules cannot pass (ie.proteins) • Smaller molecules and substances that are solulble in
lipids can pass ie. H2O, CO2, nonpolar organic molcls. • Contain enzymes for ATP production • Some membranes have photosynthetic pigments
on foldings called chromatophores
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Chromatophores
Figure 4.15 Chromatophores. - Rhodospirillum
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The Movement of Materials across Membranes
• Passive processes: substances move from high concentration to low concentration; no energy expended
• Active processes: substances move from low concentration to high concentration; energy expended
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Passive Processes
• Simple diffusion: movement of a solute from an area of high concentration to an area of low concentration ie. H2O
• Continues until molecules reach equilibrium
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Outside
Plasma membrane
Inside
Simple diffusion through the lipid bilayer
Figure 4.17a Passive processes.
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Passive Processes
• Facilitated diffusion: solute combines with a transporter protein in the membrane
• Transports ions and larger molecules across a membrane with the concentration gradient • Usually inorganic molecules too hydrophilic to pass
through the interior of the lipid bilayer. • Common in prokaryotes; non specific.
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Nonspecific transporter
Facilitated diffusion through a nonspecific transporter
Facilitated diffusion through a specific transporter
Transported substance Specific
transporter
Glucose
Figure 4.17b-c Passive processes.
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Extracellular enzymes • When a molecule is too large to be taken in,
bacteria degrades the molecule into manegable subunits • Proteins into amino acids (proteases) • Polysaccharides into monosaccharides (lactase,
cellulase, maltase)
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Passive Processes
• Osmosis: the movement of water across a selectively permeable membrane from an area of high water to an area of lower water concentration
• Through lipid layer • Aquaporins (water channels)
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Aquaporin (rapid transport of water)
Osmosis through the lipid bilayer (left) and an aquaporin (right)
Figure 4.17d Passive processes.
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Passive Processes
• Osmotic pressure: the pressure needed to stop the movement of water across the membrane
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Glass tube
Rubber stopper
Rubber band
Sucrose molecule
Cellophane sack
Water molecule
At beginning of osmotic pressure experiment
At equilibrium
Figure 4.18a-b The principle of osmosis.
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Passive Processes
• Isotonic solution: solute concentrations equal inside and outside of cell; water is at equilibrium
• Hypotonic solution: solute concentration is lower outside than inside the cell; water moves into cell
• Hypertonic solution: solute concentration is higher outside of cell than inside; water moves out of cell
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Cytoplasm Solute Plasma membrane
Cell wall
Isotonic solution. No net movement of water occurs.
Water 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).
Figure 4.18c-e The principle of osmosis.
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Active Processes
• Active transport: requires a transporter protein and ATP; goes against gradient
• Group translocation: requires a transporter protein and phosphoenolpyruvic acid (PEP); substance is altered as it crosses the membrane
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Cytoplasm
• Semitransparent elastic substance inside plasma membrane
• 80% water • Major structures
• Nucleoid • Ribosomes • Reserve deposits called inclusions
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Nucleoid
• Contains single long double stranded DNA called Bacterial Chromosome
• Up to 20% of the cell is the nucleoid (when actively growing).
• Plasmids – extrachromosomal DNA. • Replicate independently of bacterial chromosome • Contain 5-100 genes • Not crucial for survival in normal conditions, but may
contain genes that give advantage to cell ie. Antibiotic resistance.
• Can exchange plasmids sexually with other bacteria (same species usually).
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Ribosomes
• Protein synthesis • 70S = 50S + 30S
• Made up of proteins and ribosomal RNA (rRNA). • Antibiotics like streptomycin and gentamicin attach to
the 30S subuint. • Erythromycin and chloramphenicol attach to the 50S
subunit to interfere with protein synthesis.
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Inclusions
• Metachromatic granules – inorganic phosphate storage
• Polysaccharide granules – store glycogen and starch
• Lipid incuisons • Sulfur granules • Carboxysomes – contains the enzyme ribulose
1,5-diphosphate carboxylase (CO2 fixation) • Nitrifying bacteria and cyanobacteria
• Gas vacuoles • Magnetosomes (iron oxide inclusions)
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Endospores
• Some gram-positives like Clostridium and Bacillus form resting cells when nutrients are depleted • Clostridium tetani, C.perfringes, B. anthracis
• Heat, desication, exposure to chemicals • 40 mya endospore germinated • Process is called sporulation • Germination can be caused by high heat or
“germinants”. • Important to food industry and from a clinical point
of view.
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Magnetosomes
IN PLANT CELL ONLY
Vacuole
Cell wall
Chloroplast
Centrosome:
IN ANIMAL CELL ONLY
Pericentriolar material Centriole
Lysosome
Basal body
Flagellum
Idealized illustration of a composite eukaryotic cell, half plant and half animal
Peroxisome
IN PLANT AND ANIMAL CELLS
Nucleus
Nucleolus
Rough endoplasmic reticulum
Smooth endoplasmic reticulum
Microtubule
Microfilament
Mitochondrion
Plasma membrane
Ribosome
Cytoplasm
Golgi complex
Figure 4.22a Eukaryotic cells showing typical structures.