151 lec 7

• BACTERIA

  • Prokaryotic cells that are important in human disease and health
  • Can cause disease and are also part of the human microbiota
  • Structure is less complex due to a lack of:
  • Nucleus
  • Membrane bound organelles (mitochondria, endoplasmic reticulum, and Golgi complexes)
• CELL ENVELOPE

  • Several layers surrounding the bacterial cell
  • Capsule
  • Acts as a shield against phagocytosis and helps adhesion
  • Important virulence factor (lack a capsule = less virulent)
  • Cell wall
  • Found on the outer surface of cell membrane
  • For protection of bacteria
  • Consists of peptidoglycan
  • Gram-positive - has a thick layer of peptidoglycan above plasma membrane; allows retainment of staining dye
• Gram-negative


  Has a thin layer of peptidoglycan between the surface membrane and plasma membrane; cannot retain the staining dye
• Gram-negative


  • Helps maintain bacterial shape
• Cocci


  • Round-shaped
• Bacilli


  • Rod-shaped
• Spirilla


  • Spiral-shaped
• Pleomorphic


  • Multiple forms
• Plasma membrane


  Most important layer as it encloses the cytoplasm
• Cytoplasm


  Gel-like substance that composed of water, cell components, enzymes, and organic molecules
• No plasma membrane = spill of contents = no cell
• Cell relationship with outside world

  1. Acquiring nutrients

  2. Eliminating waste

  3. Maintaining interior of bacteria in constant organized state
• Selectively permeable membrane


  Allows certain molecules and ions to pass through the cell while preventing the movement of others
• Plasma membrane

  • Responsible for respiration
  • Responsible for photosynthesis
  • Responsible for synthesis of lipids and cell components
• Ribosomes


  • Sites of protein synthesis
  • Spread in the cytoplasm - produce proteins that are destined to remain inside the cell
  • Attached to plasma membrane (plasma-membrane associated ribosomes) - make proteins for cell envelope and get transported outside the cell
• Nucleoid


  Irregularly shaped region that contains the cell's chromosomes or genetic material
• Chromosomes


  • Mostly single circle of double stranded DNA (ds-DNA) but some have linear and have more than 1
  • Contain genes needed for protein synthesis in the cell
• Plasmids


  • Small ds-DNA that are independent of the chromosome
  • Can be circular or linear
  • Have relatively few genes and genetic information is non-essential to bacterium; cells that lack them usually function normally
  • Can confer a selective advantage to the bacteria (increase resistance to antibiotics)
• EXTERNAL STRUCTURES

  • Pili hair-like structures that allow them to attach to other cells
  • Fimbriae - smaller / shorter pili
  • Flagella - long, whip-like protrusions that allow movement of bacteria
• Eukaryote


  Organism with membrane-bound structures
• Prokaryote


  Organism without membrane-bound structures
• Eukaryotes


  • Have a membrane-bound nucleus that stores genetic information (DNA)
  • Have membrane-bound organelles like mitochondria and Golgi apparatus
• Prokaryotes


  • DNA is bundled up in a section of the cell called the nucleoid, which is not membrane-bound
• Eukaryote


  "kernel" or "nut" referring to the nucleus
• Structures present in eukaryotes but absent in prokaryotes

  • Mitochondria
  • Golgi Apparatus
  • Nucleolus
• Nucleolus


  Looks extra dense/dark in a micrograph, where ribosomal RNA (rRNA) is being produced
• Ribosomes


  Essential for the translation or construction of proteins based on information of mRNA, made up of ribosomal RNA and proteins
• • Eukaryotes multicellular organisms
  • Animals
  • Plants
  • Fungi
  • Protists
  • Prokaryotes single-celled organisms
  • Bacteria
  • Archaea
• BACTERIAL MORPHOLOGY

  • Coccus spherical (ex. Streptococcus)
  • Diplococci paired cells (Neiseria gonorrhoeae)
  • Streptococci cocci in chains (Streptococcus pneumoniae)
  • Staphylococci cocci in cluster (Staphylococcus aureus)
  • Bacillus rod-shape (Escherichia coli)
  • Spirochetes snake-like (Treponema pallidum)
  • Coccobacillus oval (Bordetella pertussis)
  • Filamentous mold-like (Nocardia asteroides)
• BACTERIAL CELL STRUCTURES

  S-LAYER

  • Variably demonstrated ordered protein layer
  • Gives protection and immunologic function to bacteria
  • Tight layer of mosaic cells made of many identical proteins
  • Rigid coat
  • Functions:
  • Molecular sieve
  • Protection
  • Adherence
  • Immune evasion
• CAPSULE OR SLIME LAYER

  • Sticky outermost layer made of polysaccharides
  • Help deter phagocytosis as they are slippery and protect against degradation of phagolysosomes of macrophages and neutrophils
  • Functions:
  • Adherence
  • Prevents cell from drying out
  • Evasion of immune system
• Cell wall


  Basic structure consisting of polysaccharide glycan chains with tetrapeptide or longer side-chains that are cross-linked through peptide bonds
• Peptidoglycan layer


  • Alternating amino sugars cross-linked by transpeptidase
  • Thick with teichoic acid
• Lipopolysaccharide


  • Found in gram-negative bacteria
  • O antigen
  • Core polysaccharide
• Functions of cell wall


  • Protection
  • Structural strength
• Gram-stain


  The dye is non-covalently bound to negatively charged molecules in the cell and forms a macromolecular complex with teichoic acid with crystal violet addition
• Gram-positive


  • Complexes are formed
  • Have a thick cell wall
  • Will stain purple
• Gram-negative


  • Washed out by decolorizers (solvents, acetone)
  • Secondary dye is needed to colorize the unstained gram-negative
  • Have a thin cell wall
  • Will stain red
• CYTOPLASMIC MEMBRANE

  • Selectively permeable (lipids and proteins)
  • Forms a bilayer
  • Hydrophilic exteriors
  • Hydrophobic interior
  • Functions:
  • Permeability barrier
  • Preventing leakage of cytoplasmic metabolites into the environment
  • Carrier for metabolic enzymes for transport, DNA replication, and oxidative metabolism
  • Gateway for transport of nutrients in and out of the cell
• FIMBRIAE OR PILI

  • Composed of glycoproteins for adhesion to cell surface 
  • Sex Pili - for attachment during conjugation
  • Short, hair-like appendages composed of protein subunits (pilins)
  • Functions:
  • Adhesion
  • Prevents cell from drying out
  • Evasion of immune system
  • Attachment (somatic pili)
  • DNA exchange (sex pili)