Question

Coronavirus Reproductive Cycle (part a and part b)

1. Using what you know about viral reproduction, arrange the following descriptions of the Coronavirus reproductive cycle into the correct order (number them and paste them into your response).

• The viral envelope and host membrane fuse, allowing the mixing of viral and host cell materials
• New viral particles exit the cell via exocytosis and become wrapped in membrane that forms the viral envelope
• Viral RNA replication, transcription and translation occur
• Spike proteins in the viral envelope attach to receptors on the host cell membrane.
• Viral RNA and protein come together to form a particle.
  • The current Coronavirus causing COVID-19 is a specific strain of Coronavirus called SARS-CoV-2. It is part of a group of viruses that has been known to cause a variety of intestinal and respiratory diseases in animals and, previously, mostly minor colds in humans. Each strain has specific host animals/tissues that it targets. Think about Viral Reproduction. Which step determines the host range of each strain. Explain your answer.

Answer 1

a) The viruses don not divide on their own but for their division, they utilize the host cell machinery for their reproduction and it takes place in the following order.

The order of events in the coronavirus reproductive cycle:

1. Spike proteins in the viral envelop attach to receptors on the host cell membrane. To reproduce the first important step is entry of the virus into a host cell which is done by binding of viral spike protein to the cell surface receptor.
2. The viral envelope and host membrane fuse, allowing the mixing of viral and host materials. The attachment of spike protein to the cell receptor causes the release of protease from the host cell and it activates the spike protein which causes the fusion of viral envelope and cell membrane and entry of viral particles inside the cell.
3. Viral RNA replication, transcription, and translation occur. Once inside the cell virus release its genetic material in the cytoplasm. The coronavirus genetic material is single positive-strand RNA so it directly utilizes the translation machinery of the host cell and synthesizes proteins. The newly synthesized viral RNA polymerase replicates viral genetic material and increases its number.
4. Viral RNA and protein come together to form a particle. The newly synthesized viral RNA and proteins assemble together in the Golgi complex.
5. New viral particles exit the cell via exocytosis and become wrapped in a membrane that forms the viral envelope. The newly formed viral particles released from the cell via exocytosis.

b) The host range is defined as the number of organisms or species a microbe (bacteria, viruses) can infect. A virus can infect a cell only when it is able to attach to the cell surface and enter inside. This attachment occurs through the specific cell receptors which are present on the host cell surface. The SARS-CoV-2 makes its entry into the cell by binding of spike protein to the ACE2 (Angiotensin I-converting enzyme 2) receptor which is present in almost all types of cells. Therefore it is the attachment of spike proteins of the virus to the receptors on the host cell surface (first step of reproduction cycle) which determines the host range of each strain. A narrow range means a virus can infect only few whereas a wide range means a virus can a wide variety of host cell.