Question about viruses.

[thoughtudied999]

Why are viruses not considered living? They contain DNA and reproduce. I have been told that it is because they must have a host cell, but I don't see how that makes them non-living. Can anybody clear this up for me?

Thanks

[david23]

It's just a classification. There obviously have to be limits to the definition of a living organism. if you broaden the definition, u might as well include prions, or even a plasmid. It's not really anyone's fault except who ever came up with those definitions like decades ago.

You understand that a virus need a host cell, so I guess there is no need to explain the structure of a virus.

[alwaysasking]

They reproduce only in a host cell and they cannot generate energy if not in a host cell.

[victor]

they can't generate energy? do they produce ATP or else?

[alwaysasking]

They can't generate their own energy.They use the host's ATP.They also lack ability of synthesizing organic molecules.

[Darby]

There are a few other things that they lack:

- they are not truly cellular (even the ones with membranes steal it from the host cells, and many have protein coats rather than membranes).

- they neither grow nor develop - they are produced in their "final" form.

- as mentioned, free viruses have no metabolic processes.

The one about needing a host cell to reproduce seems a bit bogus, as that also applies to a lot of bacteria and protozoan parasites.

Personally, I think that a definition of "living" that excludes viruses is too restrictive, but folks can define it as they wish...

[MrMistery]

Search the forum. This issue has been discussed and over-discussed

[fscottdahlgren]

I define life as a system avoiding equilibrium. A virus sets up no concentration gradients, etc., and therefore is not alive. However, by my definition the atmosphere is alive, which a lot of people here probably wouldn't agree with (including myself).

[Tae Jun, Yoon]

Many biologists think Organisms should satisfy this condition
(a) order
(b) evolutionary adaptation
(c) response to the change
(d) regulation
(e) energy processing
(f) growth & development
(g) reproduction
: This classification was quoted in "BIOLOGY - 7th Ed"

Viruses don't satisfy many of this standard. And especially virus can't do energy processing by itself. So biologists classify virus as non-organism

[mehdi71000]

Where do they come from
Are we under modification by them?
Aliens I say

[david23]

virus evolved just like basic cells and unicellular organisms etc etc

[mehdi71000]

Have you seen them under a electron microscope they are so neat. Its like they are designed by a machine or some thing
Some are like machines like the famous phage virus i saw this picture once the needle looked like a syringe needle. Like a perfect cylinder cut at 45dgrees on th x z plane. Mind boggling.