chapter 3

Cards (42)

  • Bacteria and Archaea are different from eukaryotes in the following ways:
    • Lack of nucleus and histones in DNA packaging
    • Cell wall makeup includes peptidoglycan and other unique chemicals
    • Internal structures lack membrane-bound organelles
  • All bacterial cells possess:
    • Cytoplasmic membrane
    • Cytoplasm
    • Ribosomes
    • Cytoskeleton
    • One (or a few) chromosome(s)
  • Most bacterial cells possess:
    • Cell wall
    • A surface coating called a glycocalyx
  • Some bacterial cells may possess:
    • Flagella, pili, and fimbriae
    • An outer membrane
    • Plasmids
    • Endospores
    • Most of these structures are also observed in archaea
  • Bacteria can function as independent single-celled organisms or in groups like colonies or biofilms
    • Bacteria have an average size of 1 μm
    • Pleomorphism refers to variations in cell wall structure due to genetic or nutritional differences
  • Bacterial shapes and arrangements:
    • Cocci: spherical or ball-shaped
    • Rods: cylindrical
    • Vibrio: gently curved rods
    • Spirillum: slightly curled or spiral-shaped
    • Spirochete: spiral cell with periplasmic flagella
    • Branching filaments: some bacteria produce multiple branches off a basic rod structure
  • Arrangement of cocci:
    • Single
    • Diplococci: pairs
    • Tetrads: groups of four
    • Staphylococci or micrococci: irregular clusters
    • Streptococci: chains
    • Sarcina: cubical packets of eight, sixteen, or more cells
  • Arrangement of bacilli:
    • Single
    • Diplobacilli: pair of cells with ends attached
    • Streptobacilli: chain of several cells
    • Palisades: cells of a chain remain partially attached by a small hinge region at the ends
  • External structures of bacteria include:
    • Flagella and axial filaments for motility
    • Fimbriae and pili for attachment points or channels
  • Fine points of flagellar function:
    • Chemotaxis: movement in response to chemical signals
    • Types of flagellar arrangements: polar, monotrichous, lophotrichous, amphitrichous, peritrichous
    • Run: rotation counterclockwise for linear direction
    • Tumble: reversal of flagellum direction causing the cell to change course
  • Periplasmic flagella are found in spirochetes and are internal flagella enclosed between the cell wall and cytoplasmic membrane
  • Fimbriae are small fibers sprouting off bacterial cells for tight adhesion and colonization
  • Pili are used in conjugation between bacterial cells and can transfer genetic material
  • Glycocalyx:
    • Coating of repeating polysaccharide or glycoprotein units
    • Slime layer protects against loss of water and nutrients
    • Capsule is denser and thicker, producing a sticky character to colonies on agar
  • Specialized functions of the glycocalyx:
    • Capsules formed by pathogenic bacteria have greater disease-causing abilities and protect against phagocytes
    • Biofilms protect bacteria from dislodgement and aid in persistent colonization of medical devices
  • The cell envelope of bacteria includes the S layer and glycocalyx
  • Biofilm formation involves the development of plaque-like structures that protect bacteria from environmental factors
  • The Cell Envelope lies outside the cytoplasm and is composed of two or three basic layers that act as a single protective unit:
  • Cell wall
  • Cytoplasmic membrane
  • Outer membrane (in some bacteria)
  • The Cell Wall helps determine the shape of a bacterium and provides strong structural support to prevent bursting or collapsing due to changes in osmotic pressure
  • Certain drugs target the cell wall, disrupting its integrity and causing cell lysis (disintegration or rupture) of the cell
  • The cell wall gains its relative rigidity from peptidoglycan
  • Peptidoglycan is a compound composed of a repeating framework of long glycan (sugar) chains cross-linked by short peptide (protein) fragments, providing a strong but flexible support framework
  • Gram-Positive Cell Wall is a thick, homogenous sheet of peptidoglycan, 20 to 80 nm in thickness, and contains teichoic acid and lipoteichoic acid that function in cell wall maintenance and enlargement
  • Gram-Negative Cell Wall is a single, thin sheet of peptidoglycan, 1 to 3 nm in thickness, making gram-negative cells more susceptible to lysis
  • Nontypical Cell Walls: Acid-Fast Bacteria like Mycobacterium and Norcardia contain peptidoglycan and stain gram-positive, but the bulk of the cell wall is composed of unique lipids like Mycolic acid, which contributes to the pathogenicity of the bacteria
  • Nontypical Cell Walls: Archaea exhibit unusual and chemically distinct cell walls, some entirely composed of polysaccharides or pure protein, lacking true peptidoglycan structure or a cell wall entirely
  • Mycoplasmas naturally lack a cell wall, with sterols in the cell membrane stabilizing the cell against lysis, such as Mycoplasma pneumoniae causing "walking pneumonia"
  • The Gram-Negative Outer Membrane is similar in composition to most membranes but contains specialized polysaccharides and proteins like Lipopolysaccharide, serving as signaling molecules and receptors, including Endotoxin
  • Cytoplasmic Membrane is a lipid bilayer with proteins embedded, serving as a site for energy reactions, nutrient processing, synthesis, and regulating transport of nutrients and wastes, being selectively permeable
  • Differences in Cell Envelope Structure show that the outer membrane of gram-negative bacteria contributes an extra barrier, making them more resistant to certain antimicrobial chemicals compared to gram-positive bacteria
  • The Cytoplasm is 70 to 80% water and a complex mixture of sugars, amino acids, and salts
  • Bacterial Chromosomes and Plasmids exist in the bacterial chromosome, with DNA aggregated in the nucleoid, and plasmids being nonessential pieces of DNA conferring protective traits like drug resistance
  • Ribosomes are the site of protein synthesis, composed of rRNA and protein, with a large and small subunit together forming the bacterial ribosome
  • The Cytoskeleton in some bacteria produces long polymers of protein similar to eukaryotic cells, contributing to cell shape and being a potential target for antibiotic development
  • Endospores are dormant bodies produced by Bacillus, Clostridium, and Sporosarcina, resisting extremes of heat, drying, freezing, radiation, and chemicals that would kill vegetative cells
  • The Medical Significance of Bacterial Endospores includes pathogens like Bacillus anthracis, Clostridium tetani, Clostridium perfringens, Clostridium botulinum, and Clostridioides difficile causing serious diseases
  • Archaea are a third cell type more closely related to domain Eukarya than bacteria, exhibiting unique characteristics like extremophiles living in extreme conditions