Ch 17: Microorganisms

• Viruses

  • Not included in the classification of organisms
  • Are incredibly small
• Viruses have two primary structures

  • An outer capsid
  • An inner Nucleic Acid core of RNA or DNA
• Viral Reproduction

  1. The viral genome takes over the cell
  2. Uses the cell resources to make new viral particles
• Bacteriophage (or Phage)


  A virus that reproduces in a bacterium
• Some animal viruses have

  • Spike-shaped glycoproteins
  • An outer membrane (Envelope)
• Viruses are specific to a particular host cell
• There are 2 possible cycles of phage reproduction:

  • A lytic cycle
  • A lysogenic cycle
• The Lytic cycle has five stages

  1. Attachment
  2. Penetration
  3. Biosynthesis
  4. Maturation
  5. Release
• Stage One of the Lytic Cycle: Attachment

  Attachment of the capsid molecule to the receptor on the surface of the host cell
• Lytic Cycle: Penetration

  • Viral enzymes breaches the bacterial cell wall
  • Allows viral DNA to be injected
• Lytic Cycle: Biosynthesis

  • The virus first deactivates all host genes not needed for viral reproduction
  • "overthrows" the host cell's machinery and initiates the synthesis of viral components
• Lytic Cycle Stage Four: Maturation

  • The assembly of new viral particles occur
• Lytic Cycle Stage Five: Release

  • Viral lysozymes rupture the bacterium to release the new virus particles
• The Lytic Cycle causes the host bacteria to die
• The Lysogenic Cycle 


  • The host cell may not immediately lyse(breakdown) because the phage is latent
  • Follows the same first 2 steps of the lytic cycle
• Lysogenic Cycle Stage Three: Integration


  • Occurs as the viral DNA becomes incorporated into the host DNA
  • This latent viral DNA is called a prophage
  • The prophage is replicated along with the host DNA and is passed along to all daughter cells
  • These lysogenic cells can be triggered to enter and complete the lytic cycle
• Plant Viruses

  • Infect plants through damaged tissues
  • Spread through the plant by migrating through the plasmodesmata which interconnect plant cells
  • They're transmitted by several mechanisms
  • They cannot be controlled with chemicals, but may be with biotechnology
• Animal Viruses

  • Reproduction similar to bacteriophages
  • Enters host cell via endocytosis
  • Will shed its outer membrane
• Retroviruses

  • RNA animal viruses that have a DNA stage
  • Use reverse transcriptase to make DNA(cDNA)
• Drug Control of Human Viral Diseases

  • Very difficult to develop
  • Some drugs interfere in viral genome synthesis
  • Some drugs block reverse transcriptase in HIV
• Viroids

  • Naked strands of RNA not covered by capsid
  • Similar to viruses
  • Primarily crop diseases
  • Hepatitis D
• Prions

  • Discovered in a cannibalistic tribe(The Fore)
  • Proteinaceous infections particles
  • Prions can cause fatal neurodegenerative disorders
  • Con influence the structure of other proteins
• Protocells

  • Cell like structures complete with an outer membrane
  • May have resulted from self-assembly of macromolecules
  • May have eventually given rise to cellular life
• Some researchers believe that RNA developed before DNA
• Bacterial Forms

  Bacteria can have several shapes

  • Rod-shaped, called bacilli
  • Spherical, called cocci
  • Spiral-shaped, called spirillum or spirochete
• Bacterial Forms

  Bacteria can occur singularly or in groups

  • Chains, add prefix Strepto-
  • Clusters, add prefix Staphylo-
• Bacterial Plasmids

  Circular DNA molecules
• Binary Fission


  The reproduction of bacteria where the circular chromosome replicates and separates
• Bacterial Conjugation


  Temporary union of two bacteria for the exchange of genetic material
• Bacterial Transformation


  Occurs when a bacterium picks up free pieces of DNA from the environment
• Bacterial Transduction


  Process in which a bacteriophage transmits bacterial DNA from one cell to another
• Endospores 


  When a Bacteria is in a unfavorable environmental conditions, they can form these and can stay dormant for thousands of years
• Bacterial Photoautotrophs 


  Use solar energy and carbon dioxide to make food
• Bacterial Chemoautotrophs

  Derives energy from the oxidation of inorganic compounds such as ammonia or hydrogen gas(chemosynthesis)
• Chemoheterotrophs

  • Take in organic molecules as source of energy
  • Most likely the first prokaryotic cells on Earth
  • Are saprotrophic
  • Use enzymes to digest food externally
• Pathogens

  Bacteria that cause diseases are called pathogens
• Pathogens can cause diseases in two ways:

  1. Produce & release toxins that cause disease
  2. Adhere to surfaces and/or invade organs or cells, causing disease
• Methanogens 


  Methane-synthesizing archaea found in anaerobic environments like swamps
• Halophiles 


  Archaea that require high salt concentrations for proper growth
• Thermoacidophiles 


  live in hot, acidic environments such as hot springs and thermal vents