systematics

• There are different types of speciation, including allopatric (geographic isolation), sympatric (ecological or behavioral isolation), and parapatric (partial geographical overlap).
• The term "species" is used to describe the smallest unit that can be recognized as distinct from other units.
• Speciation occurs when two populations become reproductively isolated, resulting in the formation of new species.
• Viruses


  Noncellular, generally smaller than 200 nm in diameter, have at least two parts: capsid (outer layer composed of protein subunits) and nucleic acid core (DNA or RNA)
• Viruses


  • Cannot be classified with cellular organisms
  • Obligate intracellular parasites (cannot reproduce outside a living cell)
  • Can infect a wide variety of cells, but are very specific
• Viral reproduction


  1. Gain entry into host because portions of capsid adhere to a specific receptor on the host cell's outer surface

  2. Viral nucleic acid enters the cell and codes for the protein units inside the capsid

  3. Virus takes over metabolic machinery of the host cell
• Lytic cycle


  1. Attachment

  2. Penetration

  3. Biosynthesis

  4. Maturation

  5. Release
• Lysogenic cycle


  1. Phage becomes a prophage that is integrated into the host genome

  2. Becomes latent, and later may reenter the lytic cycle
• Reproduction of animal viruses

  1. After entry, uncoating releases viral DNA or RNA and reproduction occurs

  2. If viral release occurs by budding, the viral particle acquires a membranous envelope

  3. Retroviruses contain reverse transcriptase which carries out RNA to cDNA transcription
• Viroids


  Naked strands of RNA that can cause crop diseases
• Prions


  Protein molecules that can cause some human and animal diseases, e.g. mad cow disease
• Prokaryotes


  Include bacteria and archaea, which are fully functioning cells
• Prokaryote structure


  • Lack a eukaryotic nucleus
  • Have outer cell wall containing peptidoglycan
  • Some move by means of flagella
  • Lack membranous organelles
  • Contain nucleoid
  • May have accessory ring of DNA (plasmid)
• Prokaryote reproduction


  1. Asexual binary fission

  2. Conjugation - donor cell passes DNA to recipient cell via sex pilus

  3. Transformation - bacterium picks up free pieces of DNA from other prokaryotes

  4. Transduction - bacteriophages carry portions of bacterial DNA from one cell to another

  5. Endospore formation in unfavorable conditions
• Obligate anaerobes


  Unable to grow in the presence of free oxygen
• Facultative anaerobes


  Able to grow in either the presence or absence of gaseous oxygen
• Photoautotrophs


  Use solar energy to reduce carbon dioxide to organic compounds
• Chemoautotrophs


  Oxidize inorganic compounds to obtain energy to reduce CO2 to an organic compound
• Aerobic saprotrophs


  Decompose most large organic molecules to smaller molecules
• Gram stain


  • Procedure used to differentiate groups of bacteria
  • Gram-positive bacteria retain dye and appear purple
  • Gram-negative bacteria do not retain dye and appear pink
• Bacterial shapes


  Spiral (spirilli), Rod (bacilli), and Round (cocci)
• Cyanobacteria


  • Gram-negative bacteria that photosynthesize
  • Believed to be responsible for introducing oxygen into the primitive atmosphere
  • Lack visible means of locomotion
  • Can live in extreme environments
  • In association with fungi, form lichens
• Archaea


  • Considered bacteria until Carl Woese discovered their rRNA has a different sequence of bases than rRNA of bacteria
  • Eukarya are believed to be more closely related to archaea than to bacteria
• Archaea structure and function

  • Plasma membranes contain unusual lipids that allow them to function at high temperatures
  • Some are methanogenic
  • Most are chemoautotrophs, none are photosynthetic
  • Sometimes mutualistic or commensalistic, but none are parasitic
• Types of archaea


  • Methanogens (found in anaerobic environments, produce methane)
  • Halophiles (require high salt concentrations for growth)
  • Thermoacidophiles (reduce sulfides and survive best at temperatures above 80°C)