How do we define life?

NO, this isn't another abortion thread, this is a biology thread.

Currently we divide everyting we consider to be alive into three Domains-
Archea-Ancient bacteria
Prokaryota-Bacteria/animals with no nucleus
Eukaryota-Everything else

The problem is that this leaves viruses and prions out and no one is sure if they are alive by our definition or if they fit anywhere in this model.

Viruses containt DNA but they do not respire, feed, produce waste, or display any signs of life outside of a living medium
Prion's are just rogue, self replicating protiens.

So what do you think, are they alive?

Life is defined by simply being alive.

Viruses are not alive because they are unable to reproduce amongst themselves--they require a host cell to do so. Those other things you listed also keep viruses out of the bracket of life.

protolife?

MRS GREEN

Movement
Respiration
Sensitivity

Growth
Reproduction
Excretion
(Egestion)
Nutrition

Viruses are not organisms but bacteria are.

If they can evolve, possibly. But until then their just matter.

Originally posted by Darth Jello
protolife?

Perhaps. They still lack some very huge requirements in order to be considered life.

Life...? well, life is cool!! yeah,
I think it is cool when you know the meaning of life afterall.
the creator of heaven,earth and all things in this world.

Life is so wonderful living w/ Him *God 🙂

Originally posted by soulwinner
Life...? well, life is cool!! yeah,
I think it is cool when you know the meaning of life afterall.
the creator of heaven,earth and all things in this world.

Life is so wonderful living w/ Him *God 🙂

I think you're in the wrong class. This is Biology 101 not Theology 101.

hmm, would they be in an even greater division than domain then?
like with viruses and all other life being two separate branches coming from the same primordial ooze?

Originally posted by DiamondBullets
Perhaps. They still lack some very huge requirements in order to be considered life.

Originally posted by Darth Jello
hmm, would they be in an even greater division than domain then?
like with viruses and all other life being two separate branches coming from the same primordial ooze?

No, cuz viruses lack a nucleus as well as all other organelles needed for respiration, waste production, and reproduction amoungst themselves. They display some charactaristics of life including genetic material, basic proteins and amino acids.

Some scientists actually debate that they are their own kingdom and those oddities make them very unique in their own right. I for one, think that claim is a bit of a stretch. I would put viruses, prions and cancers in the same category--they are rogue units that can only live by causing harm to a host. No they aint parasites--a tapeworm is a parasite. Those things are a whole 'nother ballgame.

Originally posted by Valharu
Can you give some examples?

respiration

waste production

lacking organelles

lacking the ability to reproduce without a foreign host

I don't consider alive and a life to be the same thing entirely.

"There's life on Mars." If you go there expecting to find malls and starbucks, you will be wrong. There are things there that are alive, though.

-AC

well, it wouldn't be a kingdom. it would be a new classification greater than that since none of the three domains can adiquetly house viruses. Any thoughts on prions?

Originally posted by Alpha Centauri
I don't consider alive and a life to be the same thing entirely.

Good for you!

Originally posted by Darth Jello
well, it wouldn't be a kingdom. it would be a new classification greater than that since none of the three domains can adiquetly house viruses. Any thoughts on prions?

Where a cancer is a rogue cell, a prion is a rogue protein. A similar process, but on a much smaller scale.

Originally posted by DiamondBullets
respiration

waste production

lacking organelles

lacking the ability to reproduce without a foreign host

but a cell is a living, eukariotic organism. a prion has no DNA, but replicates, and in case of things such as Kuru/mad cow disease seems to do quite a bit of damage to other protiens as it replicates by rearranging them.

Prions are evil. Prions cannot be destroyed by boiling, alcohol, acid, standard autoclaving methods, or radiation. In fact, infected brains that have been sitting in formaldehyde for decades can still transmit spongiform disease. Cooking your burger 'til it's well done won't destroy them either.

you have to breakdown the protiens. tempuratures in excess of 1000 C, high molarity acids or alkali, high level ultra violet light and just about any kind of nuclear radiation or concentrated particle beam (like a laser) should do it.