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some questions about viruses

Do all viruses have a capsid and an envelope?
Do all viruses need a host to reproduce?
Always use host cell polymerases for replication of their own genetic material?
Only infect one species of host?

Reply 1

Mimir

I don't know what you mean by 'only infect one species of host.' I presume you mean Zoonosis, in which case this does in fact happen. In some cases the virus will need to mutate to a new strain in order to spread but does happen - look at 'bird flu.' Ebola originates in a species other to humans, as does HIV. So was smallpox (which came from cowpox - you must have heard the story about the milking girls catching cow pox when milking, then not catching smallpox as they'd developed immunity to a similar strain of the disease?) It's a key reason why it was essential for the production of Insulin for diabetics needed to move away from Bovine as quickly as possible.

All viruses do indeed have protection of their genetic material, capsids are classified according to their shape/structure, although some will reconstruct it using the hosts' genetic material to 'hide' their antigens from the immune system.

Viruses can survive outside a host, that's how some of them spread, but they not replicate without a host. Virus genetic material does not encode everything the virus needs to survive (ribosomes needed for replication for example).