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Chapter 4: Functional Anatomy of Prokaryotic and Eukaryotic Cells Prokaryote Pre-nucleus Eukaryote True nucleus • One circular chromosome, not in a membrane • Paired chromosomes, in nuclear membrane • No histones • Histones bound to DNA • No membrane-bound organelles • Membrane-bound organelles • Complex cell walls • Simpler cell walls • Binary fission • Mitosis (peptidoglycan in bacteria) (polysaccharide) Prokaryotic Cells: Morphology • Average size: 0.2 -2.0 µm in diameter 2.0-8.0 µm in length • Basic shapes/morphologies: Coccus (spherical) Bacillus* (rod-shaped) Coccobacillus Spiral Prokaryotic cells: Arrangements Pairs: diplodiplococci diplobacilli Chains: streptostreptococci streptobacilli Clusters: staphylostaphylococci Prokaryotic cells: Structures external to the cell wall Prokaryotic cell structures: Glycocalyx • Capsule: Glycocalyx firmly attached to the cell wall • Sticky outer coat • Polysaccharide and/or polypeptide composition Figure 4.6a • Aids in attachment of cell to a substrate • Helps prevent dehydration • Impairs phagocytosis (host defense mechanism) http://lecturer.ukdw.ac.id/dhira/BacterialStructure/SurfaceStructs.html Prokaryotic cell structures: Flagella • Cellular propellers • Three basic parts • Filament: Made of chains of flagellin protein • Hook • Basal body: anchor to the cell wall and membrane • Rotation in the basal body propels the cell Figure 4.8 Prokaryotic cell structures: Flagella Flagella Arrangement ( flagella at both poles) (tuft from one pole) (flagella distributed over the entire cell) Figure 4.7 Prokaryotic cell structures: Flagella Motility Taxis: movement toward or away from a stimulus -chemotaxis -phototaxis Figure 4.9 Prokaryotic cell structures: Flagella Motile E. coli with flourescently-labelled flagella from the Roland Institute at Harvard Prokaryotic cell structures: Axial Filaments • Axial filaments= endoflagella • Spirochete movement • Anchored at one end of a cell • Contained within an outer sheath • Rotation causes cell to move • Spiral/corkscrew motion Figure 4.10a Prokaryotic cell structures: Fimbriae and Pili • Composed of protein pilin • Fimbriae allow attachment to surfaces/other cells • Few to hundreds per cell • Pili are used to transfer DNA from one cell to another • Longer, 1-2 per cell Figure 4.11 Prokaryotic cells: The cell wall Prokaryotic cell structures: Cell Wall • Main functions of the cell wall • Prevents osmotic lysis • Helps maintain cell shape • Point of anchorage for flagella • Contains peptidoglycan (in bacteria) Prokaryotic cell structures: Cell Wall Peptidoglycan (or murein) Macromolecular network: • Polymer of a repeating disaccharide unit (backbone) • Backbones linked by polypeptides Figure 4.13a Prokaryotic cell structures: Gram-positive Cell Walls Gram-positive cell wall • Thick PG layer; rigid structure • Teichoic acids: • Lipoteichoic acid links PG to plasma membrane • Wall teichoic acid links PG sheets • Polysaccharides & teichoic acids are cellular antigens Prokaryotic cell structures: Gram-negative Cell Walls Gram-negative cell wall • Thin PG layer • Surrounded by an outer membrane • Protection from phagocytes, some antibiotics • Periplasm (contains PG, degradative enzymes, toxins) • Lipopolysaccharide (LPS) • O polysaccharide antigen • Lipid A is called endotoxin • Porins (proteins) form channels through membrane Figure 4.13b, c Prokaryotic cell structures: Cell Walls Gram-positive Gram-negative cell walls cell walls • Thick peptidoglycan • Thin peptidoglycan • Teichoic acids • No teichoic acids • Outer membrane • Lipopolysaccharide • Porins Gram stain mechanism • Step 1: Crystal violet (primary stain) • Enters the cytoplasm (stains) both cell types • Step 2: Iodine (mordant) • Forms crystals with crystal violet (CV-I complexes) that are too large to diffuse across the cell wall • Step 3: Alcohol wash (decolorizer) • Gm +: dehydrates PG, making it more impermeable • Gm -: dissolves outer membrane and pokes small holes in thin PG through which CV-I can escape • Step 4: Safranin (counterstain) • Contrasting color to crystal violet Prokaryotic cell structures: Cell Wall Atypical Cell Walls • Mycoplasma • Smallest known bacteria • Lack cell walls • Sterols in plasma membrane protect from lysis • Acid-fast cells (Mycobacterium and Nocardia genera) • Mycolic acid (waxy lipid) layer outside of PG resists typical dye uptake • Archaea • Wall-less, or • Walls of pseudomurein (altered polysaccharide and polypeptide composition vs. PG) Prokaryotic cell structures: Cell Wall Damage to Cell Walls • Lysozyme attacks disaccharide bonds in peptidoglycan • Penicillin inhibits peptide cross-bridge formation in peptidoglycan • Bacteria with weakened cell walls are very susceptible to osmotic lysis Prokaryotic cells: Structures internal to the cell wall Prokaryotic cell structures: Plasma Membrane • Phospholipid bilayer • Proteins • Fluid Mosaic Model • Membrane is as viscous as olive oil • Proteins move to function • Phospholipids rotate and move laterally Figure 4.14b Prokaryotic cell structures: Plasma Membrane Main function: selective barrier • Selective permeability allows passage of select molecules • Small molecules (H2O, O2, CO2, some sugars) • Lipid-soluble molecules (nonpolar organic) Prokaryotic cell structures: Plasma Membrane Movement across membranes: Passive Processes • Passive processes do not require energy (ATP)— involves movement down a concentration gradient • Simple diffusion: Movement of a solute from an area of high concentration to an area of low concentration • Facilitated diffusion: Solute combines with a transporter protein to move down its gradient • Osmosis: Diffusion of water down its gradient • Diffusion continues until the solute is evenly distributed (state of equilibrium) Prokaryotic cell structures: Plasma Membrane • Osmosis: Movement of water across a selectively permeable membrane from an area of higher water concentration to an area of lower water concentration • Water moving down its concentration gradient Figure 4.18 Prokaryotic cell structures: Plasma Membrane Three types of osmotic solutions: Isotonic solution [sol]solution = [sol]cell Hypotonic solution* [sol]solution < [sol]cell Osmotic lysis [sol]cell = concentration of solute inside the cell Hypertonic solution [sol]solution > [sol]cell Plasmolysis Figure 4.18c-e Prokaryotic cell structures: Plasma Membrane Movement across membranes: Active Transport Processes • Active transport of substances requires a transporter protein and ATP • Solute movement up/against its concentration gradient • Important when nutrients are scarce Prokaryotic cell structures: Other Internal Structures • Cytoplasm: substance inside plasma membrane • 80% water, contains mainly proteins, carbohydrates, lipids, inorganic ions and low-molecular weight compounds • Chromosomal DNA: single circular string of doublestranded DNA attached to the plasma membrane • Located in the “nucleoid” area of the cell • Plasmids: small, circular, extrachromosomal DNA • Genes encoded typically not required for survival under normal conditions Prokaryotic cell structures: Other Internal Structures • Ribosomes: machinery for protein synthesis (translation) • Tens of thousands of ribosomes per cell Complete 70S ribosome Prokaryotic cell structures: Other Internal Structures Inclusions: Reserve deposits Type: Contents: • Metachromatic granules (volutin) •Phosphate reserves (for ATP generation) • Polysaccharide granules •Energy reserves • Lipid inclusions •Energy reserves • Sulfur granules •Energy reserves • Carboxysomes •Ribulose 1,5-diphosphate carboxylase for CO2 fixation • Gas vacuoles •Protein covered cylinders • Magnetosomes •Iron oxide (destroys H2O2) Prokaryotic cell structures: Other Internal Structures Endospores • Specialized resting cells (metabolically inactive) • Resistant to desiccation, heat, chemicals • Can remain dormant for thousands of years • Bacillus, Clostridium genera only (Gram-positive) • Sporulation: Endospore formation • Triggered by deficiency of a key nutrient • Germination: Return to vegetative state • Triggered by physical/chemical damage to endospore’s coat http://qlab.com.au Stained pus from a mixed anaerobic infection www.textbookofbacteriology.net Functional Anatomy of Eukaryotic Cells Figure 4.22 Functional Anatomy of Eukaryotic Cells: Flagella and Cilia • Contain cytoplasm, enclosed by plasma membrane • Move in a wavelike motion Figure 4.23 Functional Anatomy of Eukaryotic Cells: Flagella and Cilia Figure 4.23a, b Functional Anatomy of Eukaryotic Cells: Cell Walls and Glycocalyx • Cell walls • Plants, algae, fungi • Polysaccharide; simpler than prokaryotic cell walls • Glycocalyx • Carbohydrates extending from animal plasma membrane • Anchored to cell membrane • Strengthens surface, aids in attachment Functional Anatomy of Eukaryotic Cells: Plasma Membrane Similar to prokaryotic PM structure and function: • Phospholipid bilayer • Selective permeability • Peripheral proteins • Passive transport processes • Integral proteins • Active transport processes EXCEPT, they contain • Sterols (complex lipids, help strengthen membrane) • Site for endocytosis (phagocytosis and pinocytosis) Functional Anatomy of Eukaryotic Cells: Cytoplasm • Cytoplasm Substance inside plasma membrane and outside nucleus • Cytoskeleton Microfilaments, intermediate filaments, microtubules • Contains organelles Specialized functions (nucleus, ER, Golgi complex, mitochondria, lysosomes, ribosomes) Functional Anatomy of Eukaryotic Cells: Ribosomes • Larger, denser than prokaryotic • Eukaryotic ribosomes: 80S Prokaryotic ribosomes: 70S • Membrane-bound pool (attached to ER) • Free pool (in cytoplasm) Functional Anatomy of Eukaryotic Cells: Nucleus • Storage for almost whole cell’s genetic information • Enclosed by nuclear envelope • Proteins bound to DNA (histones and nonhistones) Figure 4.24 Functional Anatomy of Eukaryotic Cells: Mitochondrion • Contains DNA and ribosomes (70S) • Double membrane • Inner membrane folds: cristae • Portion inside of inner membrane: matrix • Proteins involved in respiration and ATP production in cristae and matrix • Chloroplasts: enzymes for lightgathering necessary for photosynthesis Figure 4.27 Endosymbiotic Theory • Theory on evolution of eukaryotic cells’ organelles • Prokaryotes: 3.5-4 byo • Eukaryotes: ~2.5 byo • Mitochondria and chloroplasts share properties with prokaryotes • Reproduce independently of cell • Size/shape • Circular DNA • Their ribosomes are 70S