What constitutes Life?

[hallenrm]

The discussion started on - 05-19-2006, 01:21 PM , place Hypography

 

 

The discussion was initiated bySome Guy

Not knowing much about biology, I was wondering what makes something considered to be alive?

At what level is life considered to be there? Is a virus a life form? Bacteria?

How much do we know about the makeup of life? DNA?

Thanks,

 

Ronthepon was the first to respond

 

Life is separated from the lack of it by activity of DNA. If stuff is being produced, used and made an a cell, it is alive.

Viruses are considered semi-life forms, they are at the border of living and dead.

Bacteria are full scale life forms. We know so much about the makeup of life that it will leave your head spinning. DNA is a very very known thing, we know a huge lot of what it is, does, makes, etc.

 

To this hallenrm responded:

 

There is this very famous book by the reputed physicist, Erwin Schrödinger, of quantum mechanics fame it is titled What is Life?

 

Well, left to myself, I would assert, life is not made up of unique substance, living organisms have unique characteristics!

 

Infinitenow added a point

Every individual's definition will be different.

Maybe super clusters of galaxies moving in concert with one another could be considered life. For others, they might stick to the more basic plant/animal set. Just depends on the application and context of your definition.

i

 

Life's the opposite of death.

orby

 

Mercedez Benzene:

Some characteristics of life:

-Has cells

-Converts energy

-Grows

-Reproduces

 

...all living things have at least those in common. If something is missing any one of those, it is certainly not living.

 

 

At this pointed CraigD joined the discussion :

In considering the borderline cases of what is, in a conventional biological sense, alive and what is not, let’s not forget prions <http://en.wikipedia.org/wiki/Prion>.

 

If answering the live-or-not question for viruses, which are unable to reproduce without using host cells, is difficult, answering it for prions, which appear to altogether lack nucleic acids, is even more so.

 

Personally, I suspect that a black-and-white distinction between living and unliving will prove increasingly unuseful as knowledge about both molecular biology and the organization of non-biological systems increases.

 

He was followed by Infamous

It used to be common thought for science to consider a virus a nonliving entity. That view has slowly been changing over the last few years to the point where a few scientists believe that the virus may be a precursor to life.

 

The wise man JayQ opined :

Its going to be a tough question no matter where you slice it, I read an article about a group trying to create artificial life, they where given a few criteria that it had to meet: eat, grow, reproduce and evolve.

 

The cell is one of the fundamental structural units of which all living things are composed ..

 

The question "what is life " .. also produces other questions .. like "what is A life?" .. These are questions designed to explain human existence and existence beyond.. and one question will almost always lead to another question ..

 

"What is life?" .. is also one of the major questions for humanity. To define the concept of life .. one must first ask .. "What says that something lives?" .. then .. "What conditions are required for life?" .. and also .. "What does living imply?"

 

Happythestripper played a long inning:

What exactly constitutes life .. may be determined by a historical blueprint .. one half of this blue print is a genetic message to re-produce and grow .. and the other half of the blueprint .. contains environmental factors ..

 

Life may be determined as a manifestation of energy into existence. We say something lives because it is a term invented by humans..

 

Whatever the conditions may be It must be balanced and stable.. in order for life to be conceived ..

 

Conception is defined as a general set of specific instances or ideas occurring in a sequence and encoded in a self-contained memory. The definition of life being defined as the quality that distinguishes living organisms and inanimate matter.

 

This inanimate matter is akin to the single ovum cell and the functions such as growth and reproduction are responses to stimuli originating from a living organism in the environment and gifted...

 

What says that something lives? What is something? The evolution of mankind kind is encoded as knowledge in a self contained memory, which when triggered gather and repeat this knowledge in sequence from a single ovum cell containing chromosomes to an external set of corresponding chromosomes. This code is historical in context and conception is perceived as the gathering of corresponding chromosomes to function in sequence through progressive stages... We then call this "growth" ... "the gift of life". Is that something? Maybe not... As the quality of the life conceived may be distorted and the encoded sequence unable to perform the necessary functions that determine life.

 

So... life says therefore whatever the code reads and the quality of information contained and needed to distinguish particular functions on the smallest scale in sequence.

 

What conditions are required for life? Condition is defined as a state of being... and being is the result of time and space events coming together... and attractive forces seek to organize functions required for life. I say attractive forces mostly because it’s only the strongest of life forming that will survive even when the hosting environment is weak... Although the environment leads to poorer quality... so the better the quality the longer the life... Guess that means that quality is required for life and not the only state of being needed either. You would then ask what are the conditions in the environment determining the quality of the host? This would then become a question about the state of information encoded in the host and the hosting environment that proposes life. Which I may answer later...

For now I answer what does living imply? What does imply mean??

 

Suggestion?? Okay I suggest living in the moment... a moment I define as "now"... And based on this suggestion I propose... life is a combination of time and space events requiring a certain set of encoded instructions in a corresponding environment interfacing at a particular point along the continuum transforming various stages conditioned to grow in a sequential order using logic of the information contained within a single cell and historically known as nature.

 

In other words .. life simply IS

 

 

hallenrm is not to be left behind:

A living object must be exchanging all the time with other objects around.

What does it exchange?

Anything: Energy, thoughts, money, information; just to list a few.

So that includes statements, like

To make a living

Lead a fruitful life

Art of living

Extraterrestrial life

 

 

Ronthepon the youngone:

A group of cells coordinating with one another, producing extracellular matter, absorbing nutrients, growing in organisational size, producing similar forms like itself, and usually being coordinated and controlled by a 'higher' form(called observing conciousness)

 

That's how a robot would describe life

.

 

Someguy:

To get more to the point I am more interested in finding out what is the difference between something alive and dead? A rock and a bacteria?

What is it that makes it alive?

If it is just a combination of atoms that make up protiens that make up DNA?

And specifically if we know what makes it appear in these combinations?

Is DNA considered alive?

RNA?

Do we know excactly what is needed to be able to create life?

 

Ronthepon:

To be alive, a thing needs to fulfill a few criteria.

An alive thing needs to do life processes: growth, nutrition, reproduction. Respiration, excretion may be included.

 

An alive thing becomes dead when it ceases to do any life processes.

 

And anything alive is not differentiated from something dead by any special defineable tags or labels. The type of activity of the thing describes that.

 

DNA, RNA are not living. The cell is the smallest unit of life. Calling anything smaller that as living is like... saying to a human organ 'Hey, junior Joe, how's it going?'

 

To that hallenrmresponded:

Not always true Ron!

 

There are many instances when something can be termed alive, although it doesn't grow, cannot reproduce, doesn't excrete etc. At the same time we have devices that do have one or two of these features bit can't be termed as alive.

Mercedez Benzene can't resist asking

Like what? I can't think of anything that does not reproduce.

 

hallenrm responded: A mule!!!!

 

Now Questor joined the discussion too, he began with:

this question has been discussed in other threads on Hypography. the question is: at what particulate level does life exist? is it at the molecular level or lower?

an atom does not have life, carbon is an element, but when combined with other atoms in certain patterns, it can exhibit life, and is necessary for life. is life strictly a chemical interchange? if so, exactly where does the life force start? no one knows

.

 

HydrogenBond continues

I remember years ago, studying early evolution when prelife became life; This transition is assumed connected to the evolution of simple DNA or RNA replicators, before full cells formed. Someone made an interesting comment. He said that fire fits all the definitions of the DNA replicator definition of life; coverts energy, grows and reproduces.

 

Since life and death are opposites, the definition of one should be the opposite of the other. When is something considered dead? For a human, it is not when biology stops but when the heart stops beating and the brain shows no brain waves. The hair and fingernails will continue to grow even after death. As such, a human life begins when the heart starts beating and the brain waves begin. It is not based on biochemistry alone or else burying dead people with their hair and nails still growing should be considered burying them alive.

HB

Ronthepon continued with his probing questions:

So I guess the active cell theory could hold water.

Here are the points:

The cells must:

- Perform nutrition

- Perform catabolism and anabolism reactions including respiration, as normal life processes.

Lets also remember about comatose people as alive also.

hallenrm puts in a new thought

But would you like to limit the concept of life to biological cells found on Earth alone?

Couldn't some forms of life be there yhat are not neccesarily based on catabolism and metabolism

 

Questor made some very valid points:

If we are to understand life, we must first understand at which particulate level life exists. most of the posts are discussing macro events, but life is a

micro event. cells can be seen and their enzymatic activity determined. life is below this level. it is probably electro-chemical, but no one has yet found exactly where and what it is.

 

As did CraigD:

If, by “macro” we mean something on the order of 10^-8 meters (about 100 atoms), I think most posts focus on this scale, because there’s a consensus that this is the scale at which life emerges. Most of the posts tend toward a definition of life as “having metabolism”, and any smaller than this, there’s just not enough space for the structure of even such questionably “alive” biological machines as viruses. The smallest things nearly everybody would agree is alive has a diameter of about 2*10^-7 m, while most plant and animal cells are about 10^-5 m. DNA is about 2*10^-9 m wide.

Though electrochemical processes, which can be considered to occur down to the atomic crystal scale of about 10^-10 m, can be very complex and energetic, they seem lacking in the structure and information necessary to be considered even vaguely alive.

 

There’s a tradition of scientific speculation that life is a “ghost”, or a “spark” – perhaps simply an electrical one. The 1818 novel “Frankenstein”, and the current “Ghost in the Shell” anime television series, are examples of fictional exploration of these traditions, while the work or Roger Penrose . I think, however, that these traditions, while interesting, are reaching incorrect conclusions, and are, ultimately, pseudoscientific.

 

I’d argue that life is defined more by information density and complexity than by the particular biological specifics. Consider this question: which is more alive – a dish of amino acids, enzyme and heat fractured beyond any potential for cell formation or metabolism, or a computer simulation of a biological cell?

 

Currently, the smallest features of non-biological information systems are about 10^-7 m wide, 100 times larger than those of biological ones. Current computer technology is likely to shrink another 100-fold, approaching the scale of biology. Far-off computer technology involving such exotic materials as degenerate “neutronium” might vastly surpass this scale of miniaturization to something as small as 10^-14, 100,000 times smaller than biology. Such a computer could not only perform information processing equivalent to a complex biological organism, but be physically much smaller. Current, near-future, and far-future, exotic non-biological information technology is likely, I believe, to soon force a radical reevaluation of what it is to say a system is “alive”.

 

hallenrm had this to add:

To me the essential trait of any living organism is its capacity to diversify over a period of time!

 

The capacity to evolve indeed appears to be a characteristic of all life forms, including mules and ligers!!

 

If we accept this, then even any atom/molecule can be envisioned to be alive (there are a multitude of energy states, and other configurations possible for any atom/molecule !!

How's that?

 

Responding to the idea that only living beings reproduce HydrogenBond responded:

Fire can reproduce itself. It can send out baby embers who can grow into a fire that can send out embers, etc.. It can also reproduce with radiant heat, i.e., it can reproduce without matter transfer. It is like immaculant conception. It is an omivorse that can metabolize carbon, nitrogen, almost anything with energy content. It does not have cells, in the biological sense, but can cook them so they taste better.

 

The elemental basis of life is the hydrogen proton. The hydrogen proton is necessary for the properties of water and the replicating properties of the DNA. Life would not be able to reproduce without the hydrogen proton and hydrogen bonding.

 

Responding to the idea that life is based on Carbon HydrogenBond is of the opinion:

Carbon is extremely important. But its primary function is to form molecular polymers like DNA, RNA and proteins. But once they form, the dynamics of life involve the pertubations of hydrogen bonds. Both C and H have important functions with carbon defining the molecular capacitance of life molecules, such as the memory along the DNA. While hydrogen defines the backbone of the low energy dynamics by which life molecules pack, unpack, interact and react to create life.

 

Carbon follows normal chemistry by becoming the backbone for electrons. While hydrogen bonding hydrogen are sort of an another proton layer on top of the electron clouds create by carbon. This is what gives life, life. When the DNA is duplicated, the chemical reactions begin with hydrogen bonding (base pairing). This becomes the foundation for polymerization into more DNA. The new DNA create more chemical matrix for hydrogen bonding hydrogen. Life is creating hydrogen bonding potential, which reflects hydrogen bonding proton potential moving to ever increasing potential. This is the evolutionary path of life.

Ronthepon not to be left behind added:

Well. So carbon is indeed not ahead of hydrogen in the formation of life.

 

And, I have come across certain references that silicon may replace carbon in a hypothetical life form. I also saw an article on discovery.

 

As did hallenrm:

A scientific basis of life, should not only explain the presently known forms of life, but should also help in exploring further.

 

Most of the definitions of life; e.g. its ability to reproduce, or nutrition, metabolism, catabolism fall flat on this count.

 

Let me further enunciate the concept of life proposed by me.

 

Life is additive, that is, all multicellular living beings are madeup of cells, which in turn can also be termed living.

 

But why do we stop at the cellular level only, if we accepts that all atoms and molecules are also living, we step on tio a higher paradigm, that can lead to a revolution in scientific thought. In an earlier thread http://hypography.com/forums/biology/5715-organization-organism.html I had opined that one of the principal characterstic of all life forms is organization, the organization may be limited to a limited space or may not be.

 

Thus I would reaffirm my thought that atoms/molecules are living, as long as they are naturally occuring

 

Ronthepon:

You are implying that anything is living then. Because we cannot hope to create 'our own' atoms. I'm afraid then everything will be alive. The concept of differentiating things into live and non-live will be meaningless.Alive cells must be lowest unit of life. Below that level, everything is just a complex mixture and arrangement of molecules.

So here is yet another claim: Life is what is made of live cells.

 

 

HydrogenBond responded:

The cell is not technically the most basic unit of life. The mitochondia are. These little powerhouses of the cell have their own DNA and can replicate. The rest of the cell only works because of the ATP energy the mitochondria generate. The mitochondria do not need the cell as much as the cell needs the mitochondria, so it can to be alive.

 

 

To the idea that all cells are living hallenrm responded:

If such is the case, Ron, would you call a strand of hair, a speck of dandruff, or a drop of blood, alive

 

and then continued with some new thoughts:

This question must have been mediated by the ancient Indian philosophers, and to the best of my knowledge they concluded, that there is life in each and every particle that exists in the universe. They used the word Atman for life.

 

Western biologists and philosophers too, attempted to find a more specific definition of life, after the discovery of cell and cellular mechanisms, but to the best of my knowledge there is no consensus on this question.

 

So either we accept the ancient Indian wisdom, or remain confused, is our personal choice!

 

I see no great difficulty to accept that each and every particle, atomic, subatomic or subnuclear can be called alive, only then life is not the exclusive realm for biologist. One can envision various levels of organization that characterize life. And the concept of life becomes very similar to the concept of energy.

 

Someguy found it very interesting

This is very interesting but I would say would destroy the idea of life. There would be no such thing any longer. If everything is alive then nothing is dead and therefore all is the same and same would replace life.

 

A few thoughts:

Does the ability to feel pain, loss or even instinct play into what is considered life?

It seems this is a major concern when we talk about life.

What about conciousness?

Often times I envision life as the ability to act on it's own behalf. Like a virus, it acts for itself, therefore alive.

What about locomotion?

Does something that has the ability to move by itself make it alive?

 

There are interesting ideas about computers but I wonder if anything that is considered to be alive must be constituted by natural objects?

Correct me if I am wrong but doesn't a computer have to be programmed to act a certain way or have programmed boundries at the least in order to function?

That in and of itself would to me disqualify it as life.

 

 

But HydrogenBond differed:

Atoms and nucleons may not fit the definition of life since these do not reproduce but their numbers stay steady. DNA or RNA is where molecules begin to reproduce themselves. Proteins can make proteins but this usually takes a whole group of proteins working together, while the offspring proteins are usually unable to make other proteins. One needs DNA to make the templates that make the first parent proteins.

Although the DNA is the only thing that reproduces itself and is responsbile, via templates, for making the rest of the cell, then the question becomes, why isn't the DNA considered the only living part of the cell? If we take out the DNA, the cell might continue to function in a limited capacity,and appear to be aliv,e but it can no longer reproduce so it is not really alive without the DNA. But on the other hand, the DNA can not do squat without the support of the rest of the cell.

 

This almost suggests that life is a duality. However, if we look deeper what coodinates the duality is singular, it is the hydrogen proton. The cell is designed to set up a gradient potential with respect to the protons. Within this gradient the dynamics of life is expressed.

 

Someguy found it still more interesting,

is this to say that without any of these three things life would not exist? The cell, the DNA and the hydrogen proton? None of these things have life in themselves but when you put them together life is there?

Is reproduction a necessity for life?

 

hallenrm continued with his new thoughts:

If we agree that life is a concept just like energy, where does it lead to?

Energy is a concept that relates to the potential for causing a change, any change.

In the same vein Life can be a concept that relates to the potential for creation, of any form!

This definition takes care of all confusion. Cells have life because they have the potential for dividing into more cells or organizing themselves into organisms, all new forms. Biological organisms, have life because they have the potential for reproducing, both naturally and artificially!

 

Now, one may ask, what is the potential of creation in atoms and molecules? Remember, it is the atoms and molecules that organize to form biological organisms. But on a much broader point of view, atoms and molecules constitute all chemical substances <http://en.wikipedia.org/wiki/chemical%20substances>, that lead to the creation of all artifacts, devices and machines!

 

At this point Skuzie joined the discussion, he said:

Life to me is an abstract encapsulated repository of information that is able to sense and interact with the environment in an unpredictable way. In our case we are a collection of cells that each have sorted information, on top of that we have our brain that stores even more information, together this information interacts with the environment, example by absorbing energy (food). We are unpredictable of what we do in this environment (unlike a fire), the question of whether a virus is alive is a question of is a virus predictable every time, at least to me it is.

 

Life needs not be able to reproduce or be able to evolve, we are stuck in one point of view of what is life by looking at life here on earth, but there may be more exotic life out there. If someday a true AI machine with its own conscious that will be able to make its own choices is created, wouldn’t you call that life?

 

 

But HydrogenBond stuck to his guns:

All aspects of biological life can be traced to hydrogen proton potentials and gradients. For example, reduced materials are the food of life. The proton begins tightly bound to carbon and nitrogen and upon release into water gain mobility. From this proton gradient potential we get energy.

 

Within a cell, the ion pumps, especially the sodium/potassium pumps, use the lions share of a cell's energy. One of the main uses is to create an interior membrane zone of low hydrogen potential and a zone of high exterior membrane hydrogen potential. The inner potential sets up a hydrogen potential gradient with the DNA. Within this gradient the dynamics of cellular life are expressed, with flow going in both directions to attempt lower the perpetual potential (its constantly renewed). The outside potential interacts with the environment, while migration between the inside and outside of the membrane potential allows the cell to exist beyond its own boundries, into the environment.

 

When we form multicellular animals like humans, the hydrogen proton gradient potentials is established within the entire organism. For example, between nervous tissue and the blood supply, between the brain and the body. This perpetually renewed gradient potentials is what give us life. Age will alter the potential gradient. Life is just one phenomena recycled over and over almost in holographic form, where the smallest works just like the biggests phenomena. Even the interaction of groups of people are due to gradient potentials within the brains. Organizations become a way to express the collective neural potential gradients. Suvival of the fittest in animals implies the strongest neural potential need combined with the maximum potential gradient between brain and body.

HB

And so did hallenrm

The concept of life at present is exclusive, that is, something is either alive or not. The concept of life, expounded by me, is different, it can be quantitative just like the concept of energy. A thing may have more life than another, just like a running train has more energy than a stone in a garden.

 

Atoms of different elements have different amount of life, depending upon their capacity to form different molecules. Thus, atoms of carbon, hydrogen and oxygen would have much more life than atoms of say inert gases. The amount of life in an atom could be calculated from the diversity of (molecular)structures it can form.

 

Similarly a bacterial cell, would have more life than a virus, but much less life than any multicellular organism. Amongst the multicellular organisms a human being would have the maximum life; and amongst human beings creative and socially successful people can be said to have more life than dumb ones.

 

Wouldn't it be new paradigm in science?

 

But Ronthepon finds it confusing

How can something have more life than something else?

I believe that life is more of a property present in two values: 0 or 1

Something is either alive or it is not.

The degrees of lifeness as you mentioned may be markers of vitality, or activity.

There is also a concept in language called liveliness. I think that it refers to activity.

 

encouraged by the response hallenrm continues:

Well! I am introducing a new concept to override the present one!!

 

I feel that you are overriding the concept of life with that of liveliness.

 

I'm not sure if that will be useful for science. So far I have seen usefulness of the concept only in the form of Live or Dead, and never come across the need for levels of liveliness in science.

 

Skuzie added:

However, I do not assert of the fact that the concept of liveliness is a waste. It merely is not vital to science.

I like hallenrm's idea of quantifying life, but ronthepon has a good concern that is has little practical uses in the realm of science. When dealing with biology we must know whether the organism is alive or not alive, it is a boolean value, no gray areas. But at the same time when a person dies does he really die at once? many of the cells in a persons body will continue to function until they starve from the lack of energy provided. Now your cells are 'alive' and you are 'alive' in the present biological terms. The terms alive/living/life I believe are not concrete terms such as 'gravity', but are more like the term 'lake', how big does a stream have to be in order to be a lake?

 

I think that quantification would make sense at some level in science and would make things more clear when using the current living terms. Perhaps liveliness is the correct term? but I think when judging the complexity of living identities (not necessarily biological as we know them) we have to look at the amount of information the living identity encapsulates, whether information is stored as genetic nucleotides, neuron connections, or boolean bits stored on a hard drive, in the end it is all this abstract information that makes the living identity 'living'.

 

Ronthepon seems satisfied

If you look at the problem in that way, when a person dies, many of his body fuctions cease.

 

But a lot of cells may remain alive for a number of moments.

 

In those moments, we attempt to administer the so-called life saving operations.

 

How do you define a the deadness of a man?

 

That is much more loose than defining the deadness of a cell.

 

There, I agree that livliness is needed.]

 

hallenrm continues his discourse:

If a method is agreed upon, by the esteemed bodies of science, to calculate the index of life (Life Index for Everything), Which itself would be a herculean task for scientists, imagine the number of thesis that can be produced in various departments of science, calculating this index for various things. I remember, scientific journal are proliferated with such papers, viz statistical mechanical calculations, measurements of specific heat, or free energy of a reaction etc. etc.

 

This index will open a new door for reporting explorations for extraterrestrial life. The reports of these explorations could be: The LIFE on Mars is calculated to be 100, while that on Venus is 150.

 

The index could be logarithmic, for atoms it could be a single digit, for molecules double digit and for (the so called living biological organism, 4-9 digits. However, the index would not remain constant throughout the lifespan of its body. It would increase as its size grows, and plummet down in case of its death!.

 

Skuzie had a point to add:

You are correct it would be a hard task indeed, suppose we take the information approach. Every cell in our body has some finite amount of information stored its its dna, let this amount be X. We know there are around 100 trillion cells in our bodies with each cell having X amount of data. Now take the number of average neuron connections an adult human posesses, suppose the data that can be stored in these connections sums up to Y. So the average humans index of life would equal to X times 100 trillion plus Y. This sum of raw data is everything that makes us who we are. I imagine that Y must be much much much greater than X times 100 trillion since the Y is where our intelligence comes from. Thus lower organisms will have very low Y or none at all if they dont have a brain. Suppose what other methods of storage containment there could also exist to store biological data?

[kmarinas86]

Life is associated with the following:

 

Energy source.

Matter inflow and Matter outflow.

Does work.

Adaptation.

Mutiplication and division of its unit parts or as a whole.

Growth pattern.

Differentiated components.

Polymers.

Non-crystalline.

[hallenrm]

Those are some of the attributes life is commonly associated with, but these attributes are neithe exclusive nor always neccessary for all forms of living beings known. They also are of little help for exploring unknown forms of life!!

[kmarinas86]

Those are some of the attributes life is commonly associated with, but these attributes are neithe exclusive nor always neccessary for all forms of living beings known.

 

Energy source. DUH all life needs that.

Matter inflow and Matter outflow. DUH required for growth.

Does work. DUH energy*distance=work.

Adaptation. DUH all life is adapted to their niche enviornment. It is risky when they step outside safe bounds.

Mutiplication and division of its unit parts or as a whole. (A living thing is made of one or more cells (whatever the molecular structure) which each possessing instructions for assembling assemblers (ex. proteins).)

Growth pattern. DUH although some individuals may reproduce, others of the same species will not.

Differentiated components. DUH life cannot consist of one type of atom only.

Polymers. Less obvious. Genetic code must be made of long chains suitable for encoding or decoding.

Non-crystalline. Less obvious. Crystals are not capable of adapting to the enviroment.

[hallenrm]

Very true indeed! those are the attributes by which we recognize life today on the Earth, but are they useful for looking for life elsewhere, are they really capable of solving very many riddles that still stump many a scientists?

[Rade]

Life is self initiated action of matter and energy mediated by information (within nucleic acids).

[hallenrm]

No, Rade, life is never self initiated:)

[HydrogenBond]

One thing that is left out is life needs water to exist. There are hypothetical life that use other solvents, but these only exist on paper. No substitutes for water has ever worked within a cell, and allowed all the functions of life.

 

We can take DNA out of a cell and the cell can still do everything required of life except reproduce. But if we remove the water, all the criteria of life are lost. We can substitute for water, to get a few back, but it is no longer considered alive.

[lawcat]

Why not simply: any organic entity capable of reproduction through DNA. So for life, an entity would have to be (1) organic, (2) reproductive, and (3) have DNA. If all three, then it is life.

So, for example, a dead man would have (1) and (3) as an entity, but could not (2) reprodcuce. It would not be life. But parts of a dead man, if viewed as a separate entity could still be life. (Of course, on earth generally, the "organic" requirement would be surplusage in definition.)

[HydrogenBond]

Another component of life is the requirement of water. Many tests have demonstrated that we can not substitute any other solvent, for the water within a cell, and get the life requirements that have been listed. Other solvents have been proposed, for a separate chain of life, but only on paper.

[Rade]

No, Rade, life is never self initiated:)

OK, use self generated if you do not like self initiated. What makes the fertilized egg alive ? It is the motion of matter and energy that occurs in a moment of time (e.g., it divides into two), and continues over time into the future, the cause of which derives from the self (e.g., the time sequence of the motion of "becoming" is directed by nucleic acids). There are no living things on earth that do not meet my definition of life, and no dead things that do. It is the definition that should be the first thing taught in a general biology class, which is the scientific study of life. So, class, what are we going to study in biology this year ? We will study all those entities that exist on earth that have self generated and self sustaining action over time mediated by a type of computer code found within nucleic acids. And they all have a goal, to continue to exist as a living entity, to continue playing the game.

[Rade]

Another component of life is the requirement of water. Many tests have demonstrated that we can not substitute any other solvent, for the water within a cell, and get the life requirements that have been listed. Other solvents have been proposed, for a separate chain of life, but only on paper.

It is not clear that water must be the universal liquid medium that supports life--see this link:

Hypothetical types of biochemistry - Wikipedia, the free encyclopedia

 

If we limit our definition of life to the requirement that water molecules be present for chemical reactions to occur, we constrain the possibility of looking for life in other liquid mediums. Neither is it required that life be carbon based. If we look for a definition of life to help us find it in other places in the universe, the presence of water should not be necessary. A good first place to look if it is present, sure, but we need to expand the options to allow for the possibility that life can exist in liquid mediums other than water.

[HydrogenBond]

Water, although simple looking as a molecule, is actually one of the most complex substances in nature. It displays 63 known anomalies, relatives to the more predictable nature of other chemical substances. What that translates to; water is the odd duck of the chemical world. It is the perfect medium for life. If you want life to happen, you need the odd duck, since it plays by different rules.

 

For example, although we know water as H2O, this structure only exists in the liquid state for about 1 millisecond. It is constantly swapping H. This is reflected in the pH effect, although not limited to this. There is no such thing as ancient liquid water, unless ancient is less than a millisecond. Life is just as restless.

[HydrogenBond]

Here is an interesting paper concerning water;

 

http://www.mdpi.com/1422-0067/10/5/2383/pdf

 

In the paper it is shown that the character of the translational and rotational thermal motions in water radically change near T H 315 K, which can be interpreted as the temperature of the smeared dynamic phase transition.

 

This smeared dynamic phase transitions amounts to a phase change in the properties of water. What the authors go on to say that this temperature of transition coordinates with the upper limit of body temperature for warm blooded creatures. It effects the way water interacts with the materials within warm blooded creatures, causing the entire system to shut down.

[Getting A Life]

The experiments involved in creating the "4 Stage Hypothesis for Origins of Life" (Urey and Miller) show that life was possibly created at a molecular level through the reactivity of certain chemicals. This supports some of the stances found in this thread.

 

1. Abiotic synthesis of organic monomers: Seawater plus gas atmosphere plus sparks discharged into system form organic monomers from chemical origins. (Experiments have since found all 20 amino acids, carbs, lipids and nucleotide monomers from this process.)

 

2. Abiotic synthesis of polymers: Solutions of monomers dripped onto hot rock, sand, or clay formed organic polymers via dehydration reactions.

 

3. Origin of self replicating molecules: Nucleotide monomers found in stage one and two form short RNA molecules, some begin to replicate.

 

4. Formation of pre-cells: Pre cells form from abiotically produced organic compounds. They have selective permeable surfaces and grow via absorption. They swell and divide, or shrink, in various salt concentrations.

 

At what point do we define life?

 

Self replication? Self-nonself recognition?

 

I think life - requires nutrition or energy (in any form that can be utilised, chemical or organic), replicates, interacts with it's environment, adapts and evolves.

 

A fluid thing, a dance that begins in extremely minute dimensions, of which the fluidity is not easily apparent except on a geological time scale or perhaps, in the forseeable future, at an atomic level.

[HydrogenBond]

Life accumulates potential energy, even though most of nature goes in the direction of lower energy. Life eats and will lower the potential energy of food molecules, just like the rest of nature. But it also continuously uses some of that energy to accumulate potential energy within its many structures. Once it accumulates enough energy, it uses this potential to drive the replication. This will discharge some of its energy, but it also makes two cells that can now accumulate twice as much energy, total.

 

With multicellular, since the cells are integrated, this one life unit defines even more potential energy accumulated in one place in an integrated way. This orientation also defines less entropy, than the same number of independent cells not being connected. Lowering of the entropy is also going in the opposite direction of much of nature, which prefers to increase entropy. This is common to life, with small molecules becoming fixed into larger integrated structures.

[Getting A Life]

Despite the natural tendency, there seems to be a need to avoid entropy for survivals sake. As human organisms this is obviously apparent, but on other levels the same type things can be seen eg: bacteria of various genus working in concert via quorum sensing. I believe entropy is a kneejerk (natural) impulse of life to seek further resources. Colonisation has so many benefits and very few problems (vector for rapid pathogen/parasite transmission, competition, infanticide).

 

Nice points HB, got me to thinking about communal life at a new angle.

 

Life is the communal effect of atoms.

 

We of gargantuan mass who chase pheremones in the ether are merely exponentially massive representations of a multi billion year old design that started with a self replicating molecule.