Viruses

They are:

• They have a protein coat- that protects genetic material in viruses Lack of organelle
• When the virus leaves the host cell, it is surrounded by its cell membrane so the immune system doesn't recognise the virus as a threat
• Aren't cells/non-living pathogens
• Usually no more than a protein coat around a strand of genetic material
• They have to bind/infect living cells (host cells) in order to reproduce (specific types of cells viruses will affect specific cells) kills it (dangerous as now body hasn't got immune response ́Complimentary in shape to receptors on surface of host cell

The Lytic Pathway (Lytic Cycle)

• Entry into Host Cell: The virus first attaches to a host cell and injects its genetic material (either DNA or RNA) into the host.
• Replication of Virus:
  • Once inside, the virus takes control of the host cell's machinery.
  • The virus forces the host cell to start replicating the virus's DNA (or RNA) and producing viral proteins, such as protein coats (capsids).
• Assembly of New Viruses:
  • The viral DNA and proteins are assembled into new virus particles inside the host cell.
• Lysis (Cell Bursting):
  • Eventually, the host cell fills up with new viruses, which causes the cell to burst (a process known as lysis).
  • The newly formed viruses are released into the surrounding area, where they can infect nearby cells, continuing the cycle.
• Speed of the Lytic Cycle:
  • The lytic cycle can be very fast. For example, norovirus can complete this process in as little as 12 hours, while Ebola may take several days.

The Lysogenic Pathway (Lysogenic Cycle)

• Integration into Host DNA:
  • In the lysogenic pathway, instead of immediately taking over the host cell's machinery, the virus inserts its genetic material into the host cell's DNA.
  • The viral DNA may either integrate directly into the host's DNA or remain as small circular pieces of DNA in the cytoplasm.
• Dormancy and Replication:
  • Once the viral DNA is inside the host DNA, the virus remains dormant and doesn't produce new virus particles immediately.
  • As the host cell divides, it copies the viral DNA along with its own DNA, passing it on to new cells.
• Activation of the Lytic Cycle:
  • At some point, due to certain triggers like stress or changes in the environment, the viral DNA can become active.
  • The virus then enters the lytic pathway, using the host cell to replicate and produce new viruses, eventually causing lysis.

Examples:

• Norovirus: Uses the lytic pathway, quickly causing symptoms like vomiting and diarrhea within hours.
• Ebola: Takes longer to complete the lytic cycle, leading to severe illness over several days.
• Phages (bacteriophages): Often use the lysogenic pathway, inserting their DNA into bacteria and later switching to the lytic cycle.