Invasion of SARS COV-2 

Having entered the body via the mouth, nose or eyes, the virus must find a host cell in order to replicate; it uses its spike proteins to enter the chosen cell. These spikes protrude and will bind to certain receptors on the host cells like a lock and key, which determines the type of cell and consequently the range of species that the virus is able to infect.

The sequence of events:

  1. The spike of SARS COV-2 virus binds to a cell receptor which is a protein called ACE2 (Angiotensin-Converting Enzyme 2) and uses this to gain entry into cells. In a healthy person the ACE2 receptor is used to chop up 2 forms of a protein called angiotensin in order to keep blood pressure stable and is found on the outer surface of cells in the lungs, arteries, heart, kidney and intestines.                                                                                                                         

  2. The protease enzyme TMPRSS2 (Transmembrane Serine Protease 2) then slices off the spike's head which allows the fusion machinery inside the spike to unfold and the SARS COV2 RNA to enter the cell.                                                                                                                                        

  3. The virus and cell membranes fuse and once inside, the  virus releases a snippet of genetic material, its RNA.                                                                                                                                                                                                                                                          

  4. The infected cell reads the RNA and begins to make proteins that will keep the immune system at bay and help assemble new copies of the virus.                                                                                                                                                                                                                        

  5. As the infection progresses the machinery of the cell begins to churn out new spikes and other proteins that will form more copies of the virus.                                                                                                                                                                       

  6. Vesicles carrying newly formed viruses merge with the cell membrane opening a channel that allows the viruses to exit. One cell can release hundreds of virus copies.                                                                                          

  7. The cell then dies either because it is killed but the immune system or its resources have been used up.                                                                           

  8. The virus may infect nearby cells or end up in droplets that escape the lungs.