Part 2

• Criteria used in classifying bacteria:

  • Capsule: a polysaccharide layer that completely envelopes the cell, offers protection, enhances the ability of bacterial pathogens to cause disease, and helps in attachment to surfaces
  • Appendages: include flagella for locomotion and pili (fimbriae) for attachment between bacteria during conjugation
  • Endospores: resistant asexual spores that develop inside some bacteria cells, highly resistant to various conditions, helpful in identifying species like Bacillus and Clostridium

  
• Prokaryotic cell characteristics:

  • No nucleus (only Nucleoid)
  • Contains peptidoglycan in the cell wall
  • No membrane-bound organelles
  • Smaller ribosomes compared to eukaryotic cells
  • Cell division through binary fission
  • Lack sterols in the plasma membrane
  • No cytoplasmic membrane containing CHO
  • No sexual reproduction through meiosis, but through bacterial conjugation
  • Presence of glycocalyx as a capsule or slime layer
• Eukaryotic cell characteristics:

  • Contains a nucleus
  • Has membrane-bound organelles
  • Does not contain peptidoglycan in the cell wall
  • Contains sterols and CHO in the plasma membrane
  • Larger ribosomes compared to prokaryotic cells
  • Cell division through mitotic division
  • Presence of cytoplasm containing CHO
  • Can undergo sexual reproduction through meiosis

  
• Structures within the cytoplasm:

  • Cytoplasm / Protoplasm: involved in protein synthesis, energy production, signal transduction, transportation of metabolites, and structural support
  • Nucleoid (Bacterial Chromosome): single long circular double-stranded DNA molecule devoid of histone protein
  • Plasmids: self-replicating extrachromosomal units of DNA containing genes that provide special characteristics to the bacterial cell
  • Ribosomes: microscopic factories for protein synthesis found in all cells
  • Cytoplasmic Membrane / Plasma Membrane: protects the cell's interior, made of fat and protein molecules, and has selective permeability
• Prokaryotic cells lack a nucleus and other membrane-bound organelles

  
• Prokaryotic cell structure includes a cell wall, cell membrane, cytoplasm, ribosomes, and genetic material in the form of a single circular DNA molecule

  
• A symporter is a protein that transports two molecules across a membrane at the same time, like transporting two sodium ions and one potassium ion simultaneously

  
• Exocytosis is a process where a cell creates a vesicle to enclose something inside the cell, for the purpose of moving it outside of the cell, across the membrane

  
• Cytoysis occurs when a cell bursts and releases its contents into the extracellular environment due to a great influx of water into the cell
• Types of Cytoysis:

  • Endocytosis: large amounts of extracellular fluid may be taken into a cell by engulfing
  • Receptor-mediated endocytosis: the cell recognizes a specific molecule it wants to take in and forms a vesicle around that area
• Divisome is a large and highly dynamic molecular machine responsible for the process of cell division
• Morphological differences in bacteria:

  • Cocci: spherical, oval, or flattened on one side, with various types like Staphylococcus sp. in clusters or Streptococcus pneumoniae in pairs with pointed ends
  • Bacilli: rod-shaped bacteria with different types like Bacillus sp. with squared ends or Salmonella sp. with round ends
  • Spirochetes: spiral-shaped bacteria with types like Leptospira sp. or Treponema sp.
  • Pleomorphic: bacteria lacking a distinct shape, like Mycoplasma sp.
• Metabolism in bacteria involves enzymes for biochemistry:

  • Endoenzymes work within the cell
  • Exoenzymes are produced inside the cell and then transported outside to facilitate the digestion of high molecular weight substrates
• Classification of organisms based on O2 requirement:

  • Obligate Aerobe: can't survive without oxygen, possess catalase, peroxidase, and superoxide dismutase enzymes
  • Facultative anaerobe: primarily aerobic but can grow in the absence of oxygen, possess superoxide dismutase and catalase enzymes
  • Microaerophilic anaerobe: only aerobic growth, requiring low oxygen concentration, possess superoxide dismutase enzymes
• Nutrition in bacteria:

  • Carbon and Energy Source:
  • Phototrophs use light as an energy source
  • Chemotrophs use chemical compounds as an energy source
  • Autotrophs use inorganic sources as an energy source
  • Heterotrophs use organic carbon as an energy source
• Temperature Requirement in bacteria:

  • Psychrophilic: grow below 10°C
  • Mesophilic: grow at 20-40°C, best at 30-40°C
  • Thermophilic: grow at 50-55°C
  • Hyperthermophilic: optimum growth at 80°C or more
• Staining characteristics in bacteria:

  • Gram-positive bacteria stain purple or blue due to a thick layer of peptidoglycan
  • Gram-negative bacteria stain red/pink due to a thin layer of peptidoglycan covered by an outer membrane