Viruses

• Viruses cannot reproduce independently
• Virus life cycle


  1. Virus particle attaches to host cell surface

  2. Virus enters host cell

  3. Virus uses host cell's enzymes to produce copies of itself

  4. Virus particles leave host cell and can infect new host cells
• Virus


  A particle much smaller than a bacterial cell, with different shapes but many are broadly spherical, ranging from 20 to 300 nanometers in length
• Common virus structures


  • Genetic material (DNA or RNA)
  • Protein capsid containing genetic material
  • Attachment proteins on surface
  • Lipid envelope (some viruses)
• Viruses are not cells, they are acellular
• Viruses cannot reproduce independently, they must invade a host cell and use the host cell's enzymes to make copies of themselves
• Viruses are not considered living organisms