microbiology

• Nucleus


  Contains the genetic material that controls the activities of the cell
• Nucleus


  • Has a nuclear membrane around it
  • Separates the nucleus from the rest of the cell
• Cytoplasm


  Helps maintain the shape of the cell
• Ribosomes


  Take and translate mRNA into the proteins needed to create proteins for the cell

  
• Golgi apparatus


  Waste disposal and recycling centre
• Golgi apparatus


  Delivers proteins and lipid molecules processed by the endoplasmic reticulum into vesicles to be distributed within or outside the cell

  
• Mitochondria


  Energy supplier for the cell
• Vacuole


  Stores things for the cell (food, water, waste)
• Centrosome


  Organises cell division
• Rough endoplasmic reticulum


  Produces and processes proteins for the cell
• Smooth endoplasmic reticulum


  Serves several processes e.g. making lipids
• Viruses are minute, infectious particles ranging in diameter from 20-300 nm

  
• Viruses are acellular - they contain no cellular organelles, cannot grow and divide, and carry out no independent metabolism - they are considered neither prokaryotic nor eukaryotic

  
• A virus particle, called a virion, is composed of a viral genome of nucleic acid (either DNA or RNA) that is surrounded by a protein coat called a capsid

  
• Many viruses that infect animals are surrounded by an outer lipid envelope, which they acquire from the host cell membrane as they leave the cell
• Viral genomes may be double- or single-stranded DNA (a DNA virus), or double- or single-stranded RNA (an RNA virus)
• Viruses have to invade living cells to reproduce and the result of viral reproduction is often the death of the host cells
• Individual types of virus have a preferred site of entry into the body
• Once within the body, the virus may either cause a local inflammation or it becomes more widely disseminated
• Many viruses have a preferred 'target cell' in which to reproduce
• Replication of the polio virus takes place within the spinal cord and death of the motor neurons results in paralysis
• The immune system may ultimately overcome the virus, but some virions can remain in the body in an inactive state and result in a series of further infections
• Viral genes may also become incorporated into the DNA of the host cell, a process leading to the development of malignant disease

  
• Bacteria are prokaryotic (no membrane-enclosed nucleus) organisms with a single chromosome (closed circle of double-stranded DNA with no associated histones)

  
• Bacteria lack a mitochondria or chloroplasts and replicate by binary fission

  
• Pathogenic bacteria are bacteria which are capable of causing disease
• Unlike viruses, bacteria possess a cellular structure and the metabolic systems necessary to derive energy from exogenous sources of nutrients
• Bacterial cells differ fundamentally from most other cells including human cells - the chromosomes are not enclosed in a nucleus, the cell wall is composed of peptidoglycan, and cellular structures such as mitochondria and chloroplasts are absent

  
• Bacteria utilise a variety of extracellular substances to grow and reproduce - sugars, amino acids, oxygen, water, temperature, pH, and inorganic ions
• When the bacterial cell reaches a certain size, DNA replication occurs and the cell divides into two

  
• Some bacteria produce spores during their life cycle usually as a response to diminishing levels of nutrients in the environment
• Spores survive for a long time in a dormant condition and are resistant to extremes of temperature, pH, desiccation and chemical agents

  
• Essential structural components of a bacterial cell

  • Chromosome (DNA)
  • Ribosomes
  • Cell membrane
  • Cell wall
  • Surface layer

  
• The macromolecules that make up cell material are DNA, RNA, protein, polysaccharide, phospholipid, or some combination thereof

  
• Macromolecules that make up cell material

  • Proteins (amino acids)
  • Polysaccharides (sugars)
  • Phospholipids (fatty acids)
  • Nucleic Acids (DNA/RNA) (nucleotides)
• Bacterial cells have three architectural regions: appendages, a cell envelope, and a cytoplasmic region

  
• Bacterial cell structures and their functions

  • Flagella (swimming movement)
  • Pili (mediates DNA transfer during conjugation)
  • Capsules (attachment to surfaces, protection)
  • Cell wall (prevents osmotic lysis, rigidity and shape)
  • Plasma membrane (permeability barrier, transport, energy generation)
  • Ribosomes (protein synthesis)
  • Inclusions (nutrient reserves, specialized functions)
  • Chromosome (genetic material)
  • Plasmid (extrachromosomal genetic material)

  
• There are two types of cell wall in bacteria - Gram positive have a thick, rigid cell wall, Gram negative have a thinner cell wall covered with a lipo-protein layer

  
• The Gram stain reaction is used to distinguish Gram positive and Gram negative bacteria
• Gram positive bacteria stain blue-purple, Gram negative bacteria stain red