Question

Describe how sub-viral entities differ from viruses and why they are studied in virology

Answer 1

Sub viral agents have certain similarities and differences with viruses and hence, are studied in virology.

The similarities include :

1. They are transmissible (infectious) in nature.

2. They both are non living outside the host and living inside the host cell.

3. They all can be crystallised.

The sub viral agents include -

A. Viriods

B. Prions

C. Satellite viruses

The difference between subviral agents and viruses include :

Feature	Viruses	Viriods	Satellite viruses	Prions
Definition	Small infectious particles which are non living outside the host but living inside it.	Completely assembled virus outside the host.	Viruses which require a helper virus for their multiplication and transmission.	Proteinaceous infectious agents without nucleic acids.
Protein	present	absent	present	present
Nucleic acid	present	present	present	absent
Helper requirement	no	no	yes	no
Infectivity	yes	yes	yes	yes

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