Prokaryotes - Cell Structures PDF

VII. STRUCTURES INTERNAL TO THE CELL ENVELOP/CYTOPLASTIC STRUCTURE Consists of aqueous solution of three groups of molecules  Macromolecules (proteins, mRNA, tRNA, etc.)  Small molecules which serve as energy sources, precursors of macromolecules, metabolites, or vitamins  Various organic and...

VII. STRUCTURES INTERNAL TO THE CELL ENVELOP/CYTOPLASTIC STRUCTURE Consists of aqueous solution of three groups of molecules  Macromolecules (proteins, mRNA, tRNA, etc.)  Small molecules which serve as energy sources, precursors of macromolecules, metabolites, or vitamins  Various organic and inorganic ions and cofactors STRUCTURAL COMPONENTS:  Nucleoid  Ribosomes  Inclusion bodies GENOME  Consists of a single, circular chromosome  lacks nuclear membrane and mitotic apparatus  Appears as diffused nucleoid or chromatin body that is attached to a mesosome (sac-like structure) RIBOSOMES  Site of protein biosynthesis and gives the cytoplasm a granular structure  Consist of RNA and proteins  70S in size and separates into two subunits, 50S and 30S  Found in the matrix of loosely attached to the PM  Matrix ribosomes – synthesis of protein that will remain in the cell  Plasma membrane ribosomes – synthesis of proteins for transport outside the cell PLASMIDS  Extrachromosomal, double-stranded element of DNA that is associated with virulence  Located in the cytoplasm and serve as a site for the genes to code for antibiotic resistance and toxin production  Not essential for bacterial growth so a bacterial cell may or may not contain a plasmid  Sometimes disappears during cell division and it can make bacteria (mostly Gram-neg) pathogenic.  Not required for growth and reproduction but carry genes which confer selective advantages: drug resistance, pathogenicity; new metabolic activities Two kinds of Plasmid:  Large Plasmid - responsible to produce β-lactamase that provide - resistance to β-lactam antibiotics (penicillin and oxacillin)  Small Plasmid - resistant to tetracyclines and chloramphenicol INCLUSION BODIES  Serve as the energy source or food reserve of the bacteria or as a reservoir of structural building blocks  Composed mainly of polysaccharides, they lessen osmotic pressure  Granules of organic or inorganic materials  Examples: glycogen, cyanophysin granules, poly-B- hydroxybutyrate granules, carboxysomes (cyanobacteria, nitrifying bacteria and thiobacilli), gas vacuoles (cyanobacteria, halobacterium and thiothrix) and polyphosphate granules(volutin and metachromatic granules) Two common types of granules:  A. Glycogen  storage form of glucose  B. Polyphosphate granules  storage form for inorganic phosphates  source of phosphate for nucleic acid and phospholipid synthesis Examples:  Babes-Ernst bodies (C. diphtheria)  Bipolar bodies (Y. pestis)  Much granules (M. tuberculosis)  Poly- β -hydroxybutyric acid (PHB)  Lipid like compound consisting of chains of β- hyroxybutyric acid units connected through ester linkages  Produced when the source of nitrogen, sulfur or phosphorus is limited and there is excess carbon in the medium  PHB and Glycogen  Carbon source when protein and nucleic acid synthesis are resumed   Sulfur granules  Hydrogen sulfide and thiosulfate ENDOSPORE  Toughest of all specialized cells  Longest surviving  Dormant for many periods of time (even millions of years)  Survive treatments that will rapidly and efficiently kill other cell forms: - 100°C, ionizing radiation, chemical solvents, detergents, and hydrolytic enzymes  Formed by deeply rooted lineages of Bacteria: - Clostridium (anaerobe) and Bacillus (aerobe)  Small, dormant structures located inside the bacterial cell  Aid in the survival of bacteria against external conditions  Produced within vegetative cells of some Gram-positive bacteria  Composed of dipicolinic acid and calcium ions: CALCIUM DIPICOLINATE  Some locations could be a means of microscopically identifying bacteria  Responsible for perpetuation, but not multiplication  Examples: Bacillus and Clostridium Types of spores according to location: a. Terminal spore= Clostridium tetani  b. Subterminal spore= Clostridium botulinum c. Central spore= Bacillus anthracis  Transformation of endospore to vegetative cell: activation, germination, outgrowth  Endospore Formation 1. Growth stops and DNA is duplicated 2. A Septum forms dividing the cell asymmetrically 3. Larger compartment engulfs smaller compartment 4. Peptidoglycan-containing material is laid down between 2 membranes  5. Mother cell degraded and endospore is released Structure of Endospore 1. Core - spore protoplast  contains a complete nucleus (chromosome), all the components of the protein-synthesizing apparatus, and an energy-generating system based on glycolysis  2. Spore wall/ core wall - innermost layer surrounding the inner spore membrane  contains normal peptidoglycan and becomes the cell wall of the germinating vegetative cell  3. Cortex - thickest layer of the spore envelope  contains an unusual type of peptidoglycan, with many fewer cross- links than are found in cell wall peptidoglycan  4. Spore Coat - composed of a keratin-like protein containing many intramolecular disulfide bonds  Impermeability of this layer confers on spores their relative resistance to antibacterial chemical agents 5. Exosporium - composed of proteins, lipids, and carbohydrates  consists of a paracrystalline basal layer and a hair like outer region Example: B. anthracis and B. cereus VIII. STRUCTURES EXTERNAL TO THE CELL ENVELOP 1. GLYCOCALYX  Outward complex of polysaccharide on the bacterial surface and other cells  Helps the bacteria to attach to the surface of the solid objects or tissues  Appears as a capsule or a slime layer  A gelatinous polymer (usually a network of polysaccharides)  extending from the surface of the bacteria to other cells IMPORTANCE  Protection against ion and pH changes and osmotic stress  Protection against certain enzymes  Protection against predacious bacteria and phagocytes  Enhances virulence of pathogenic bacteria TYPES  Capsules -layer is well-organized and not easily washed off  Slime layer - unorganized, diffused and easily removed A. CAPSULE  Organized and is firmly attached to the cell wall  Immediately exterior to the murein layer of gram-positive bacteria and the outer membrane of gram- negative bacteria  Made up of polysaccharide polymers  Exception: Poly-D-glutamic acid capsules of Bacillus anthracis and Bacillus licheniformis  Protects the bacteria (virulence factor) from the attacks of human defense system since it resists phagocytosis and desiccation  Capsules sometimes must be removed to detect the somatic (cell wall) antigens present  Capsule removal is accomplished by boiling a suspension of the microorganism  Does not ordinarily stain with use of common laboratory stains, such as Gram or India ink→appears as a clear area (“halo”-like) B. SLIME LAYER  Unorganized material that is loosely attached to the cell wall  Made up of polysaccharide  Can either inhibit phagocytosis or aid in the adherence of the bacteria to the host tissue or synthetic implants facilitates and maintains bacterial colonization of biologic (e.g., teeth) and inanimate (e.g., prosthetic heart valves) surfaces through the formation of biofilms Extracellular Polymeric Substance (EPS)  helps cells in a biofilm attach to their target environment and to each other  protects the cells within it, facilitates communication among them, and enables the cells to survive by attaching to various surfaces in their natural environment HOW ARE BIOFILMS FORMED: 1. Attachment 2. Growth 3. Detachment 2. FLAGELLA  exterior protein filaments that rotate and cause bacteria to be motile  complex structures, mostly composed of the protein flagellin, intricately embedded in the cell envelope  thread-like appendages composed entirely of protein, 12–30nm in diameter  plays an important role in survival and the ability of certain bacteria to cause disease  antigenic (H antigens), and some of the immune responses to infection are directed against these proteins  Gliding motility: Capnocytophaga, Cyanobacteria, Myxobacteria Flagellum is attached to the bacterial cell body by a complex structure consisting: A. Hook - short curved structure that appears to act as the universal joint between the motor in the basal structure and the flagellum B. Basal body - bears a set of rings, one pair in gram- positive bacteria and two pairs in gram-negative bacteria C. Filament - long outermost region constant in diameter and contains the globular (roughly spherical) protein flagellin arranged in several chains that intertwine and form a helix around a hollow core Motility- ability of an organism to move by itself  “Run" or “Swim” - bacterium moves in one direction for a length of time  "Runs” - interrupted by periodic, abrupt, random changes in direction called "tumbles”, then, a "run" resumes  "Tumbles”- caused by a reversal of flagellar rotation ARRANGEMENT OF THE FLAGELLA  a. Atrichous - without flagellum  b. Monotrichous - single flagellum at one end  c. Amphitrichous - single flagellum at both ends  d. Lophotrichous - tuff or group of flagella on one end or both ends  e. Peritrichous - entire cell surface covered with flagella 3. AXIAL FILAMENTS  bundles of fibrils that arise at the ends of the cell beneath an outer sheath and spiral around the cell  anchored at one end of the spirochete  have a structure like that of flagella  Rotation of the filaments produces a movement of the outer sheath that propels the spirochetes in a spiral motion  Movement is like the way a corkscrew moves through a cork Note!!! SPIROCHETES  group of bacteria that have unique structure and  motility move by means of AXIAL FILAMENTS OR ENDOFLAGELLA 4. FIMBRIAE  Short fine, hair-like appendages in many gram-negative bacteria (can reach up to 1,000/cell)  not involved in motility  Some aid in attachment of bacteria to solid surfaces  Enable cells to stick to surfaces, including animal tissues in the case of pathogenic bacteria, or to form pellicles (thin sheets of cells on a liquid surface) or biofilms on solid surfaces  Notorious human pathogens in which fimbriae assist in the disease Process  include Salmonella species (salmonellosis), Neisseria gonorrhoeae (gonorrhea), and Bordetella pertussis (whooping cough). 5. PILI  Hair-like, proteinaceous structures that extend from the cell membrane into the external environment; some may be up to 2μm  long  Hair-like microfibrils usually produced by flagellated Gram- negative bacteria observable by electron microscopy  serve as adhesins that help bacteria attach to animal host cell surfaces, often as the first step in establishing infection  composed of structural protein subunits—pilins TWITCHING MOTILITY  a pilus extends by the addition of subunits of pilin, makes contact with a surface or another cell, and then retracts (power stroke) as the pilin subunits are disassembled---grappling hook model  Results in short, jerky, intermittent movements  Example: Pseumdomonas aeruginosa, Neiss ia gonorrheae, and some strains of E. coli COMMON PILI OR ORDINARY PILI  Play a role in bacterial adherence to surfaces thus contributing to virulence SEX PILUS  serves as the conduit for the passage of DNA from donor to recipient during conjugation  present only in cells that produce a protein referred to as the F factor  F-positive cells initiate conjugation only with F-negative cells, thereby limiting the conjugative process to cells capable of transporting genetic material through the hollow sex pilus Note!!! Streptococci  fimbriae are the site of the main surface antigen---M protein  Lipoteichoic acid, associated with these fimbriae, responsible for the adherence of group A streptococci to epithelial cells of their hosts  N. gonorrhoeae  able to make pili of different antigenic types (antigenic variation)