Describe the modes of viral multiplication.

1. Adsorption / Attachment
- A virus encounters a susceptible host cell and attaches to specific receptors on the cell membrane
- The receptors are glycoproteins the cell requires for its normal function
e.g. HIV virus attaches to CD4 protein on certain white blood cells.
- Cells that lack compatible virus receptors are resistant to adsorption and invasion by that virus.

2. Penetration and uncoating
- The flexible cell membrane of the host is penetrated by the whole virus or its nucleic acid.
- Through endocytosis the entire virus is engulfed by the cell and enclosed in a vacuole.
- The enzymes in the vacuole dissolve the envelope and the capsid uncoating the virus
- This process releases the viral nucleic acid into the cytoplasm

3. Synthesis (Replication and protein production)
Viral nucleic acid exerts control over the host’s synthetic and metabolic machinery. This varies depending on whether the virus is DNA or RNA.
- DNA virus enters the host cell’s nucleus where they are replicated and assembled (except the retroviruses).
- RNA viruses are replicated and assembled in the cytoplasm
- Some viruses come equipped with the enzymes for synthesis of viral components while others utilize those of the host.
- The nucleic acid RNA or DNA is synthesized using the host nucleotides
- Proteins for the capsid, spikes and viral enzymes are synthesized on the hosts’ ribosomes using its amino acids.

4. Assembly (Host cell as factory)
Mature virus particles are constructed from the growing pool of parts toward the end of the cycle.
- The capsid is first laid down as an empty shell that serves as a receptacle for the nucleic acid strand.

5. Release of mature viruses
Assembled viruses leave their host through either of those two days.
(a) Non enveloped viruses released when the cell lyses or raptures
(b) Envelope viruses are released by budding from the membranes of the nucleus or vesicles

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Kavungya answered the question on March 12, 2019 at 13:29