viruses

• a virus is a tiny, infectious agent that can only replicate inside the living cells of a host organism
• viruses are not considered living organisms, why is this?

  they lack cellular structure and cannot carry out metabolic processes on their own. they must hijack the machinery of a host cell to reproduce
• viruses are not affected by antibiotics
• what is a capsid?

  the protein shell that encases and protects the genetic material
• viruses are made up of what?

  small subunits called capsomeres. the arrangement of these protein subunits may vary , giving the capsid its specific shape and form
• icosahedral capsids consist of 20 triangular faces
• helical capsids have a rod-like or spiral structure
• some viruses have more elaborate capsids, (complex) these can have multiple components
• what is the nucleic acid genome ?

  the complete set of genetic material present in an organism or virus
• the nucleic acid genome contains all of the instructions necessary for the development, functioning and reproduction of and organism or virus. it dictates how the virus infects host cells and replicates
• types of genomes:

  • double stranded DNA - herpesvirus or adenovirus
  • single stranded DNA - parvoviruses
• what is the viral envelope?

  a lipid membrane that surrounds the capsid of some viruses
• the viral envelope is a key factor in how viruses infect host cells and evade the immune system
• the viral envelope is made up of a lipid bilayer that comes from the host cells cell/plasma membrane , nuclear membrane or internal organelles
• embedded within the lipid bilayer are viral glycoproteins or spikes, what is their function?


  proteins that protrude from the envelope and are crucial for recognising and binding to receptors of the host cell
• what are bacteriophages ?

  the viruses that infect and replicate within bacteria
• bacteriophages are found in soil, sewage, water and other places where bacteria live. these viruses help keep bacteria growth in check in nature
• when does a viral infection occur?

  when a virus enters the body, invades host cells, and begins to replicate, causing harm to the host organism
• a viral infection can spread via:

  • direct contact - skin contact or bodily fluids
  • inhalation - breathing in viral particles
  • ingestion - contaminated food or water
  • vector transmission - bites from insects
• signs and symptoms of viruses only show when cells are damaged