what is life?

[nutronjon]

Surely you have discussed "what is life" at least once if not more often, but the thread "muscle fatigue and shaking" made me want to ask the question again.

We do not consider chemical reactions life. We do not think of electricity as life. However, when chemical reactions involve electrical impulses we have life? Like there is Frankinstien's body rotting in a grave, obviously continuing the chemical process of decomposition helped by living microisms, and Frankstien brings this body back to life with a jolt of electricity. Or, it could be the person who had a heart attack who is jolted back to life. Whatever- organic matter is not exactly a living life form, unless there is an electrical impulse flowing through it? Without this spark of life, the organic matter decomposes and looses the intrigety of its form.

[Tolouse]

electric impulses is just energy that has been changed

but once its released and unable to return, that form is said to be dead

dead battery, dead cells, dead person

energy spent, energy transferred

well, my 3 cents anyways

[Thunderbird]

Originally Posted by nutronjon

Surely you have discussed "what is life" at least once if not more often, but the thread "muscle fatigue and shaking" made me want to ask the question again.

We do not consider chemical reactions life. We do not think of electricity as life. However, when chemical reactions involve electrical impulses we have life? Like there is Frankinstien's body rotting in a grave, obviously continuing the chemical process of decomposition helped by living microisms, and Frankstien brings this body back to life with a jolt of electricity. Or, it could be the person who had a heart attack who is jolted back to life. Whatever- organic matter is not exactly a living life form, unless there is an electrical impulse flowing through it? Without this spark of life, the organic matter decomposes and looses the intrigety of its form.

The question is to my way of thinking a "Non Sequitur" you could describe internal functions that keep something alive, but to gain any meaning one needs to ask... What does life do? what is its function in relation to a system that it finds itself in? This does not necessarily mean purpose, but what is its nature?, what trends and patterns can be observed? what is its intent as a force of nature?

[HydrogenBond]

One way to address life is to see what it the most critical component. Life, as we know it, would not be possible without water. One can switch proteins or genes to get the variety of life, but there is no substitute for water. There are no life forms on earth that use a water substitute. A seed that is de-hydrated is not alive, until we add water. However, water by itself is not alive. But the impact of this one simple molecule makes everything else in the seed come alive. What makes water unique is hydrogen bonding.

What we do next is go through the cell to see if hydrogen bonding is important to anything besides water. As it turns out, just about everything makes use of hydrogen bonding either directly or indirectly. The DNA would be useless without hydrogen bonding. All we need to do to prove this is substitute the H with something else to see if it makes a difference. We can still make large DNA look-a-like macromolecules but they will just sit there totally inanimate. There is no substitute for the hydrogen bonding.

To further test the importance of hydrogen bonding, for life, is to apply enough heat to something alive to disrupt the hydrogen bonding, but not enough to break any covalent bonds and harm the large bio-materials such as proteins and the DNA. For example, if we heat an egg, it can never come alive again, if the hydrogen bonding is not just right, even if we don't harm the big molecules. This suggests bio-materials make life possible, but only if they make use of hydrogen bonding with this hydrogen bonding having to be just right. If we mess this up with heat or other means we will not get life even if their basic chemical composition is not altered .

This is the common feature between water and bio-materials, with the bio-materials needing to get their hydrogen bonding just right so it can interact with the hydrogen bonding within the water, to create life. We can heat water to kill bacteria, so we can mess up this specific hydrogen bonding to end life, without necessarily changing the primary molecules. We will mess up their secondary and tertiary structure based on hydrogen bonds.

All and all, hydrogen is the key of life. Life is not just DNA, it is an integrated process dependant on water and hydrogen bonding. Common sense would say since H is so critical and since H is everywhere with its little hand on the pulse of every operation, the H is the basis of life. There is no substitute for the H, without it, we have blob of dead nothing even if it contains DNA and protein. It has to get H-bonds just right.

[HydrogenBond]

If you look at a single DNA molecule, it is useless for life. It only becomes useful if it hydrogen bonds to another DNA molecule to form the double helix. Let us take an enzyme that is fully functional. We stretch it out and then randomly push it back together into a ball similar to before. We have not altered the carbon-nitrogen backbone. It will not work nor will it be able to participate in life. It has to have a certain configuration with the hydrogen bonds very specifically arranged. To coin some new terminology it needs a certain configurational potential at the level of h-bonds to be useful as part of life. If not, it is garbage ready for the recycle bin.

We can even do it differently. We push it together, but take great care to make sure its active site looks exactly like it did. If it works at all, it functionality becomes very limited. Without the correct configurational potential, working in support, the energetics of the active site changes. Logically, this implies there is a potential set up within the proper hydrogen bonding that helps the active site do what it has to do, better. Even a tweak like left and right hand protein h-bonded helixes make all the difference because it alters the configurational potential needed to support the active site. It is not as simple as life is based on carbon. That backbone is playing a support role for hydrogen bonding. The goal is to perfect and coordinate the hydrogen bonding to get an integrated system we call life.

Next, we reverse engineer to see if the opposite is true. Or whether hydrogen bonding helps make it possible to form the carbon backbones. For example, the DNA makes use of hydrogen bonding templates to create a new DNA molecules whose activity will also be based on hydrogen bonding. All the support enzymes are also based on hydrogen bonding, with optimized configurations, able to break and form covalent bonds, using H-bond potential. If we mess the H-bond configurational potential they don't work right and can't break or form covalent bonds with any reliability. This implies proper H configurational potential makes it possible to make the C backbone. The hydrogen takes on a life of its own, creating the underlying potential that leads to the carbon backbone, needed to expand the role of H, so it can make even more C backbone, etc. If we mess up the role of H, then the system comes to a grinding halt even if we leave the C backbones untouched. This same schema works at every level of the cell, allowing the entire cell comes to life, with all the subsystems showing an integration.

[nutronjon]

I thank the powers that be, that I found this site, and I am glad I asked the question. Every reply was a thoughful one. I don't want to derail this thread with discussion of how important your good manners are, so I will start another thread that under humanities and philosophy. But in case you don't get there, know, and feel, my deep apreciation for your good manners and thoughtful replies.

Thunderbird's, question, "What does life do" is a perfect set up for HydrogenBond's explanation.

As for the other answers, I spent my day wondering when a bean is dead. Vegetation can start dying soon after it is fully grown, but life remains in the seed. I find this pretty awesome. It is also mind stretching to think "What does life do". I really, really like that question.

Man, these thoughts make me want to get out and exercise! Remember the "muscle fatigue and shaking" thread ? Strenuous exercise causes the muscles to break down and rebuild + when vegetation becomes fully grown it begins to die. Conclusion, we must inactivate the growing force to prolong our lives. In a lab dish, human cells reproduce enough times for a 130 year life span. We have the potential to live 130 years. But our complexity means a lot can go wrong and the rate of decline skyrockets when we pass 80. Awe, thinking "What does life do" pushed my thinking in this direction.

I can't resist- am I the only one who can't avoid thinking about God when asking the question what is life? Especially your answers push me to ask the big question. The life forums in other forums are not so impressive and I have thought the shorter their spans, the better. The thinking in this forum makes me think it would be a good thing if we live 130 years or longer, because the potential of the people here is awesome. If God were Hydrogen, and I am responsible to this God, what does that responsibility look like? What does life do? I love you guys. You are really awesome.

[Rade]

I define life as being: "self-generated action mediated by nucleic acids". The definition clarifies the status of the virus as being alive.

[Moontanman]

Originally Posted by nutronjon

Surely you have discussed "what is life" at least once if not more often, but the thread "muscle fatigue and shaking" made me want to ask the question again.

We do not consider chemical reactions life. We do not think of electricity as life. However, when chemical reactions involve electrical impulses we have life? Like there is Frankinstien's body rotting in a grave, obviously continuing the chemical process of decomposition helped by living microisms, and Frankstien brings this body back to life with a jolt of electricity. Or, it could be the person who had a heart attack who is jolted back to life. Whatever- organic matter is not exactly a living life form, unless there is an electrical impulse flowing through it? Without this spark of life, the organic matter decomposes and looses the intrigety of its form.

We do not consider chemical reactions to be life? On the contrary that is exactly what life is. Life is a chemical reaction that by combing chemicals from it's environment and using the energy of these and other chemicals to grow and reproduce. What we know as bacteria are not the earliest life forms or example of life. Bacteria are actually quite complex. We really can't say if DNA is necessary or if water is the only solvent or even if carbon is the only scaffolding life can build around. We have only one example of life, it is more than possible our life isn't the only type. Electricity is used by complex life to send signals to the muscles. This electricity is generated by chemical reactions. No spark of electricity is required for a bacterium to live and reproduce. Even what we would call dead meat contains still living cells. If they are stimulated by electricity they can be made to contract but this is destructive and repeated attempts to make this happen will kill the cells. Electrical stimulation can help restart the heart but this doesn't put the breath of life back into a dead body. If the brain is dead or if the body is to far gone all the electricity in the world will not bring back any function at all. The heart is just a pump, you can live without the heart if you have an external pump.

[CraigD]

Originally Posted by Thread title

what is life?

The essential trait that distinguishes living from non-living is, as best I’ve been able to reason it, self replication. Simply put, all living entities, be they cells within a larger organism or autonomous organisms, are able to make, from ambient sources of matter and energy, similar or identical copies of themselves.

By this definition, a virus – which by definition cannot replicate without using the reproductive factory of a host cell – is not living, while, in principle, a self replicating non-biological machine (AKA a “von Neumann probe”) – which by definition can – is.

At present, self-replicating non-biological machines are practically hypothetical. Although contested claims of success have been made, all of these prototype machines require specially manufactured feed stock and/or none has successfully produce a copy of itself able to produce another copy, due to a high incidence of errors. I can see, however, no reason to conclude that such will always be the case, and expect that continued research will eventually result in a non-biological machine able to independently manufacture copies of itself, which by my definition will qualify it as living. Truly successful self-replicating non-biological machines will, I strongly suspect, be for many design generations many orders of magnitude less efficient, in terms of energy and material used and speed of self-replication, than biological organisms, and hardly adaptive at all.

This definition of life, inclusive of the possibility of non-biological entities, brings out I think some interesting food for thought.

Ignoring the contribution of humans, nearly all common collections of machines constitute self-replicating organisms. For example, a 19th century factory can, in principle, and with a few atypical additions, such as spinning wheels, looms, and sewing machines, be used to make all of the tools needed to build another factory. So the difference between collections of ordinary machines and a self-replicating machine is, in a practical sense, one of degree of automation.

Loosely analogously, a large, complex biological organism like a human being cannot survive long without a host of symbiotic, genetically foreign biological organism (eg: mitochondria and intestinal flora and fauna) to assist in its “manufacturing operations”.

A key distinction between the dependence of a factory on human operators and a human body on symbiotic organisms appears to me that we humans are, I think we’d nearly all agree, much smarter than our helper organisms, while a factory is much dumber. Another is that helper organisms are, compared to the difference between a human being and a drill press, very similar to their host’s bodies by virtue of having DNA and being generally “wet and squishy”.

[InfiniteNow]

Craig offers one concept above, and did quite well at explaining (as per usual ).


However, in the context of abiogenesis (life from non-life), the definition I've seen most commonly used in biological circles (as opposed to trigonometrical squares ) is that something alive must have all four of the following characteristics:

1. Metabolism (both anabolism and catabolism)
2. Response to stimuli
3. Growth
4. Reproduction


I've read that many researchers in the abiogenesis field have added a fifth characteristic:

5. RNA/DNA directed protein synthesis


Further, some other researchers even add a sixth characteristic for their purposes:

6. Has a lipid bilayer membrane.


The challenge really is finding a clear and consistent way of categorically separating the living thing from it's environment.


I personally have ascribed closely to the first four listed above. However, as Craig's post shows, other researchers discard the first three conditions and define something as "alive" if it can self-replicate.