Question

Briefly describe the six-step life cycle of animal viruses.

Answer 1

Answere :

Six steps in the multiplication of animal viruses are :

1. Attachment : It is first step where viruses attach to cell membrane of host animal cell. Virus encounters host cell and adsorbs specifically to the receptor sites on the cell membrane. Glycoprotein spikes on the envelope bind to the cell membrane receptors.

2. Penetration : It is a step where virus penetrate into host cell by Endocytosis (pinocytosis) or fusion. The entire virus is engulfed by cell and enclosed in a vacuole.

3. Uncoating : In this step virus uncoating occurs by viral or host enzymes. Enzymes in the vacuole dissolve the envelope ( the virus is said to be uncoated) and capsid, releasing the virus into the cytoplasm.

4. Biosynthesis : At this step, production of nucleic acid and proteins by host cell for virus takes place through replication and protein synthesis. Proteins for the capsid, spikes, and viral enzymes are synthesized on the host's ribosomes using its amino acids.

Mechanism of biosynthesis varies depending on whether the virus is a DNA or RNA virus. RNA viruses replicate in the cytoplasm whereas DNA viruses replicate in the nucleus.

5. Maturation : In this step, nucleic acid and capsid proteins assemble into new virions in host cell.

6. Release : It is the last step of animal virus life cyce where it release by budding process (enveloped viruses) or rupture the cell to release (non-enveloped viruses). Now, new virus particles infect another cells.

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