chapter 3 - Chapter 3: Prokaryotic Cell Chapter 3:...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Chapter 3: Prokaryotic Cell Chapter 3: Prokaryotic Cell Structure & Function Bacterial Cell Morphology Bacterial Cell Morphology Coccus: sphere Bacillus: rod Vibrio: gentle curve, comma Spirilla or Spirochete: helical Pleomorphic: can change shape Appendaged: have tubes or stalks Bacterial Cell Arrangements Bacterial Cell Arrangements Individual cells Diplo­ pairs Strepto­ chains Staphylo­ clusters Tetrads­ squares of 4 cells Sarcina­ cubical packets of 8 cells Bacterial Morphology & Bacterial Morphology & Arrangements Bacterial Cell Sizes Bacterial Cell Sizes Escherichia coli: 1.0 µm by 2.0 to 6.0 µm long, average bacterium size, vertebrate intestines Nanobacteria: approx 0.2 µm diameter, most are uncultured Giant bacteria: Epulopiscium fisheloni: 80 µm x 600 µm long, surgeonfish intestines Thiomargarita namibiensis: 100 to 750µm diameter, ocean sediments Prokaryotic Cell Organization Prokaryotic Cell Organization Internal Structures Cell Envelope Protoplasm Nucleoid Ribosomes Inclusions Endospores Cytoplasmic membrane Cell Wall Glycocalyx S­layers Appendages Flagella Fimbriae and Pili Prokaryotic Cell Organization Prokaryotic Cell Organization Prokaryotes: Internal Structures Prokaryotes: Internal Structures 1. Protoplasm (Cytoplasm) Cell pool for all biosynthetic functions Mixture of sugars, amino acids & salts 70­80% water Enzymes Prokaryotes: Internal Structures Prokaryotes: Internal Structures 2. Nucleoid (Chromosomal dsDNA) Usually a single circular chromosome Vibrio cholerae has more than one Borrelia burgdorferi has linear chromosome Unbound by any internal membrane Usually diffuse but sometimes condensed Prokaryotes: Internal Structures Prokaryotes: Internal Structures 2. Nucleoid cont. 0.6­10 million base pairs in length, 1000X longer than cell if stretched out Unwinds for replication & expression Contains essential genes Evidence for attachment to inner side of cytoplasmic membrane Plasma membrane or mesosomes may help in separation of duplicated chromosome during fission Nucleoid Structure Nucleoid Structure Prokaryotes: Internal Structures Prokaryotes: Internal Structures 3. Plasmids (extrachromosomal dsDNA) Contain genes that enhance survivability Replicate independently of chromosome Can also integrate within bacterial chromosome (genetic recombination) Circular, like chromosome Unattached to membranes Prokaryotes: Internal Structures Prokaryotes: Internal Structures 4. Inclusions Granules (organic or inorganic material) or membranous (gas) vesicles Often visible with light microscope Formed for storage purposes primarily – each inclusion body stores different substances Prokaryotes: Internal Structures Prokaryotes: Internal Structures 4. Inclusions cont. Poly­ß­hydroxybutyric acid ­ lipid­like, stored carbon and energy source; found in purple photosynthetic bacteria Glycogen – starch­like, stored carbon and energy source; found in many bacteria Volutin – polyphosphate reservoirs, also called metachromatic granules; found in many bacteria Sulfur granules – energy and electron source; found in purple photosynthetic bacteria Prokaryotes: Internal Structures Prokaryotes: Internal Structures 4. Inclusions cont. Cyanophycin granules­ polymer of aspartic acid and arginine (amino acids) stored nitrogen source; found in cyanobacteria Carboxysomes­ contain ribulose­1,5­ bisphosphate (Rubisco) for CO2 fixation; found in cyanobacteria, thiobacilli and nitrifying bacteria Magnetosomes in magnetic bacteria­ not a storage product, allows orientation for navigation toward nutrients Prokaryotes: Internal Structures Prokaryotes: Internal Structures 4. Inclusions cont. Gas vacuoles – aggregates of many gas vesicles Made of a single protein Impermeable to water but permeable to gases Provides buoyancy for aquatic bacteria Alter depths in water to obtain proper light intensity or oxygen levels Inclusion Bodies Inclusion Bodies Prokaryotes: Internal Structures Prokaryotes: Internal Structures 5. Endospores Develop within vegetative cells during unfavorable growth conditions For surviving environmental extremes Heat, drying, radiation, pH extremes Common isolates of soil and rock environments, aquatic sediments, mud, deserts Clostridium (tetanus, botulism, gangrene, lockjaw) Bacillus (anthrax) Most species with spores are Gram+ Prokaryotes: Internal Structures Prokaryotes: Internal Structures 5. Endospores cont. Spores have a VERY low water content and are metabolically inactive as a result Sterilization techniques must eliminate spores­ some can survive an hour’s boiling Recovered from both ancient mud (>7500 years old) and fossilized amber Found that spores could still germinate to produce viable cells Prokaryotes: Internal Structures Prokaryotes: Internal Structures 5. Endospores cont. Contain dipicolinic acid (15%) Previously thought responsible for heat­resistance Dipicolinic acid mutants have been isolated and still form resistant spores Calcium­dipicolinate may stabilize spore nucleic acids Contain some DNA repair enzymes and DNA binding proteins Prokaryotes: Internal Structures Prokaryotes: Internal Structures 5. Endospores cont. Dormant spores transform to vegetative cells Three stages: activation, germination and outgrowth Activation: usually by heat Germination: spore swells and spore coat ruptures; loses resistance Outgrowth: spore protoplast synthesizes new components and returns to vegetative cell state Bacterial Endospores Bacterial Endospores Prokaryotes: Cell Envelope Prokaryotes: Cell Envelope 1. Cytoplasmic membrane Boundary between a cell and its environment Dynamic interface Changes with temperature, age, environment Hydrophobic tails Hydrophilic heads Flexible, phospholipid bilayer sheet May contain steroid­like molecules: hopanoids to stabilize structure Prokaryotes: Cell Envelope Prokaryotes: Cell Envelope 1. Cytoplasmic membrane cont. Membrane Proteins: Peripheral: Loosely connected to the cytoplasmic membrane Hydrophilic nature Integral Amphipathic­ have both hydrophilic and hydrophobic portions Extend from within the cytoplasm into the exterior environment Cytoplasmic Membrane Structure Cytoplasmic Membrane Structure Prokaryotes: Cell Envelope Prokaryotes: Cell Envelope 1. Cytoplasmic membrane cont. Regulate transport of sugars, salts, other metabolites into cell & export of proteins Site for interaction of enzymes in pathway Assists in chromosomal DNA replication? Mesosomes = internal invaginations of cytoplasmic membrane Serve as chromosome attachment points during cell division Cytoplasmic Membrane & Mesosome Cytoplasmic Membrane & Mesosome Mesosome Prokaryotes: Cell Envelope Prokaryotes: Cell Envelope 2. Cell Wall Required to withstand osmotic pressure from within and prevent cell from bursting (lysing) and also confers cell shape Approx. 75 psi­ constantly in aqueous environment with low [solute] About 100 different types known but two major groups: Gram+ & Gram­ Share in common peptidoglycan but usually thin layer in Gram– and thick layer in Gram+ Prokaryotes: Cell Envelope Prokaryotes: Cell Envelope 2. Cell Wall cont. Peptidoglycan backbone: 2 amino sugars linked together in alternating units N­acetylmuramic acid (NAM) N­acetylglucosamine (NAG) Prokaryotes: Cell Envelope Prokaryotes: Cell Envelope 2. Cell Wall cont. Peptidoglycan strength and rigidity increased by formation of cross­linked tetrapeptides between layers of the amino sugar backbone Diaminopimelic acid (DAP) unique to bacteria found in Gram ­ links to D­alanine directly Interpeptide bridges (5 glycine residues) form between D­alanine and L­lysine between the two opposing tetrapeptide chains Peptidoglycan Structure Peptidoglycan Structure Gram – peptidoglycan cross­linking Gram + peptidoglycan crosslinking Bacterial Cell Walls Bacterial Cell Walls Gram + Cell Walls Gram + Cell Walls Very thick layer of peptidoglycan May have a very thin, discrete periplasmic space Teichoic acids present­ unique to Gram + bacteria Polymers of ribitol­P or glycerol­P, additional sugars and amino acids Connect to the peptidoglycan molecules via a covalent bond with NAM (i.e. fencepost) Some have added proteins (lipoteichoic acids) and connect to the cytoplasmic membrane lipids Gram + Cell Walls Gram + Cell Walls Gram ­ Cell Walls Gram ­ Cell Walls Peptidoglycan layer is much thinner Covered by an outer membrane Contains porins: provide channels for smaller molecules to pass through Braun’s lipoproteins anchor outer membrane to peptidoglycan layer Outermost edge consists of lipopolysaccharides (LPS) Periplasmic space exists between outer membrane & cytoplasmic membrane Contains thin peptidoglycan layer Gram ­ Cell Walls Gram ­ Cell Walls Gram ­ Cell Walls Gram ­ Cell Walls Lipopolysaccharide Lipid portion (Lipid A) Anchors molecule to outer membrane Fatty acids attached to a disaccharide Causes endotoxic shock Very powerful biological activity Core polysaccharide O­polysaccharide­ varies within strains Sugar portion Gram ­ LPS Structure Gram ­ LPS Structure Cell Lysis & Peptidoglycan Strength Cell Lysis & Peptidoglycan Strength Preventing synthesis of peptidoglycan is an effective way to control new microbial growth No new peptidoglycan = no new cell wall = no new cells via binary fission If peptidoglycan strength is compromised, cells cannot prevent osmotic pressure from bursting cells open Existing cells are lysed, preventing microbial growth of existing cells Antibiotics & Peptidoglycan Antibiotics & Peptidoglycan Penicillin = antibiotic which inhibit peptidoglycan synthesis Binds to proteins involved in cell wall synthesis to prevent crosslinking of glycan chains More effective on Gram positives than Gram negatives Amount of peptidoglycan in cell walls LPS excludes penicillin Lysozyme & Peptidoglycan Lysozyme & Peptidoglycan Lysozyme = enzyme which weakens peptidoglycan strength Natural antimicrobial found in tears and saliva Breaks the bonds between NAM and NAG in the peptidoglycan chains Decreases rigidity of the cell wall as peptidoglycan is removed Either a protoplast (Gram +) or a spheroplast (Gram ­) is formed Spheroplasts still have outer membrane and are a bit more stable under osmotic pressure Cell Wall & Gram Stain Chemistry Cell Wall & Gram Stain Chemistry LPS is dissolved by alcohol decolorization in Gram negatives, leaving peptidoglycan layer Alcohol may dehydrate the peptidoglycan­ makes pores smaller Depth of peptidoglycan on Gram + bacteria acts as extreme barrier so purple dye complex stays inside Thinness of peptidoglycan in Gram – bacteria allows easier loss of dye from within cells Differences in the cross­linking of glycan chains may cause different pore sizes in the bacterial cell wall Less stereochemistry in Gram – bacteria may allow crystals to be washed free Cells must excrete certain proteins to the outside environment = secretion Plasma & Outer Membrane Plasma & Outer Membrane Permeability Exoenzymes Gram + transport only through plasma membrane Gram ­ must transport through both the plasma membrane and the outer membrane All secretion paths require energy: ATP/GTP hydrolysis Proton motive force Protein Secretion ­ 1 Protein Secretion ­ 1 Sec­Dependent (General) Secretion In both Gram+ and Gram – organisms Transported as pre­proteins with a signal peptide at NH2­terminus Sec machinery recognizes this signal Chaperones (SecB) bind to delay folding of proteins SecA protein acts as a motor to translocate only the preprotein across membrane using ATP hydrolysis Signal peptide is cleaved from preprotein as it emerges from the cytoplasmic membrane the outside/periplasmic space Folding occurs to form mature protein Sec Dependent Secretion Sec Dependent Secretion Protein Secretion ­ 2 Protein Secretion ­ 2 Other Secretion Systems in Gram ­ Organisms Type II Common in pathogens Transports: cellulases, pectinases, proteases, lipases and toxins across outer membranes from the periplasmic space Transport proteins across outer membrane from the periplasmic space Some form channels on their own = autotransporters Some require a separate helper protein Type V Protein Secretion ­ 3 Protein Secretion ­ 3 Other Secretion Systems in Gram – Organisms (cont.) Type I (ABC Transport) Use C­terminal signals for recognition of new proteins Spans cytoplasmic and outer membrane – no Sec transport needed Transports proteins as well as many solutes, sugars and amino acids Also aids in expelling drugs from cytoplasm Protein Secretion ­ 4 Protein Secretion ­ 4 Other Secretion Systems in Gram – Organisms (cont.) Type III Transports directly from the cytoplasm to cell exterior – no Sec transport needed Transports: toxins, phagocytosis inhibitors, apotopsis promoters, secretions regulatory proteins Type IV Secrete both proteins and DNA (for conjugation) Bacterial Secretory Systems Bacterial Secretory Systems Prokaryotes: Appendages Prokaryotes: Appendages 1. Glycocalyx Polysaccharide layer external to cell wall Not produced by all bacteria Synthesis is usually regulated Storage and/or protection i.e. slime layer, caspule, sheath Prokaryotes: Appendages Prokaryotes: Appendages 1. Glycocalyx cont. Slime layer Capsule Sheath Loose & soluble Protects against drying Biofilm formation Thick and tightly bound Antiphagocytic and protects against drying Attachment Can be protein Highly organized external layer Protects against disruption by current and dispersal Prokaryotes: Appendages Prokaryotes: Appendages 2. S­Layers Found on some Gram+ and Gram­ bacteria and common among Archaea In Gram – bacteria, adheres directly to outer membrane In Gram + bacteria, associated with the peptidoglycan In Archaea, may be only cell wall component present Prokaryotes: Appendages Prokaryotes: Appendages 2. S­Layers cont. Regularly structured layer of protein or glycoprotein patterned like floor tiles Protects against: pH fluctuation Osmotic stress Hydrolytic enzymes Predators such as Bdellovibrio Prokaryotes: Appendages Prokaryotes: Appendages 3. Flagella Confer swimming motility in liquids E. coli = 270 rps Vibrio alginolyticus = 1100 rps Slender, rigid, threadlike propellers extending from bacterial surface 20 nm diameter x 15­20 um length Not found on all bacteria Complex protein structure made of flagellin Prokaryotes: Appendages Prokaryotes: Appendages 3. Flagella cont. Polar or nonpolar arrangements Internal flagella Typically, only Gram – have these Called an endoflagella or an axial filament Winds around cell within periplasmic space Found in spirochetes:Treponema pallidum (syphillus) & Borrelia burgdorferi (Lyme disease) Prokaryotes: Appendages Prokaryotes: Appendages 3. Flagella cont. Filament (thread) Hollow, rigid, helical cylinder Growth occurs at distal end; subunits move down hollow core and assemble spontaneously (self­ assembly) Anchored to cell wall Motor for rotation, spins like a propeller Hook Basal Body Prokaryotes: Appendages Prokaryotes: Appendages Prokaryotes: Appendages Prokaryotes: Appendages 3. Flagella Movement Bacteria swim through the rotation of flagella M ring rotates freely in plasma membrane Some evidence that the S ring is fixed within the cell wall in Gram + bacteria Movement not driven by ATP synthesis like for eukaryotic flagellar rotation Na+ or H+ gradients and electron transport chain are thought to provide energy Prokaryotes: Appendages Prokaryotes: Appendages 4. Fimbriae and Pili Short hairlike external appendages Thinner than flagella Functions: Fimbriae attach bacteria to solid surfaces­ Dental plaques Pilus (pili) involved in bacterial conjugation Allow transfer of plasmids from one bacterial cell to another Pilus and Fimbriae Pilus and Fimbriae with fimbrae fimbrae Pilus and Fimbriae Pilus and Fimbriae ...
View Full Document

This note was uploaded on 03/24/2009 for the course MIBO 3500 taught by Professor Dustman during the Fall '09 term at University of Georgia Athens.

Ask a homework question - tutors are online