Hallo John

I found the attached consideration (pd-File) quite interesting)

Have a look

Regards

Frank

Hi John,

defining life is far from being easy. Although viruses are not considered living entities by most, they may as well be classified as living: Everything depends on the definition of life. I tend, not to rely solely on metabolism as primary criterion for life but rather on having an evolutionary history, distinct from others. This definitely holds true also for viruses. In that respect, it doesn't matter too much that phages' or viruses' metabolisms are borrowed from the host.

By the way: What do you make of obligate intracellualr parasites? They, too, borrow major parts of their metabolism from the host. Are they living? How do we look at frozen cells, or at resting Bacillus spores? Are they living? Probabl not as long as they are frozen or nearly completely desicated, at least not with respect to metabolic activity. For teaching it proved much more convincing, over the years, to refer more to the individual evolutionary history than to all the other criteria.

Distinguishing information storage from life is indeed a niice addition to the general problem. A synthetic genome must not necessarily be regarded as living, but, as has been done, if introduced into a DNA-free bacterial shell, it may immediately provide all the usual criteria of life.

Maybe, most of the problem is really due to our definitions of life.

Nice problem that you address - best wishes, Johannes.

I am not an expert in this field, but after reading your phrase "A synthetic genome must not necessarily be regarded as living, but, as has been done, if introduced into a DNA-free bacterial shell, it may immediately provide all the usual criteria of life" - I became curious - does it mean that even after having synthesized an "working" genome you still need a not "artificial" nature-made shell to provide the life criteria?

yes - the information in the DNA is not enough.

Yes, this I can understand, but in such a case, a logical conclusion would be than even without a "genome" an "intrinsic" vitality creating properties should be recognized for the environment into which the artificial genome is being introduced, which exists in other cell components (shell, etc.)... or, in other words, that no life can be artificially created even providing all synthetic components...!? If one is able to synthesize these other components chemically would it work...? Probably, I am going too far beyond the current understanding, but this is how the science develops - asking always what if...?

Yes Svetlozar,

artificial life isn't that artificial after all. Before being given into a cell (a well-designed in vitro system may be adequate for expressing some (!) functions, normally attributed to life), a genome corresponds more to something that John described as "information storage". I am very critical about the "intrinsic life" concept. If you write down the AGCTs of a Genome in a publication or in a book, would this meet your ciew of "intrinsic life". Not so easy. - I never thought to much about synthesizing components of living cells other than RNA or DNA. Maybe it is not impossible. Modern life, however, doesn't need this. And first life on earth started at a much lower complexity with much less functions.

Yes, Johannes, That`s exactly what I was thinking - that "artificial" life is not that artificial after all... Modifying (already naturally created) cell hosts by genetic engineering by using "synthetic" genomes is only semi-artificial and we are still very far (if possible at all) from the completely artificial life concept...

I am a novice here. But here are some points: (1) Jack Szostack's lab can make lipid vesicles (protocells) that grow and divide. (2) With advances in proteomics and metabolomics, it should not be difficult to delineate all proteins expressed and metabolites present in a simple bacterium. (3) It should also not be very difficult to make all the repertoire of the recombinant proteins--in not now, then in near future--and mix them all into a defined recepe, (4) Venter's group have already gone down to the basal, minimum genetic information required for a bacterium, and have synthesized it and have replaced the natural DNA with the synthetic ones. Now, can these many groups of researchers someday put these stuff together within the protocell and see how that goes? That will be some challenge, but I guess that's where these people are going.

By the way, I would tend to define life as "the ability to act". An iron rod is non-living; no matter where you put it, it cannot act. So is a knife; it cannot cut a piece of wood all by itself, unless we use it to. However, ribozymes can act. Enzymes can act. So can a virus. In my perspective, even an enzyme is "alive" (otherwise, why do we have the concept of "catalytically DEAD mutants?). Here, I would exclude chemical reactants. They do not "act", instead, they undergo molecular redesigning/modifications readily explainable by atomic structural architecture. I sure sound naive!

Even if what I said in the 1st paragraph turns true in near/distant future, that will not be enough to say that "humans created a living being". Because, the majority of components would have been directly derived from those existing in the nature already. A true synthetic ability would be to start from the scratch with phosphate, ammonia, methane etc., and go all the way "synthetically" to the final "artificial cell". This I think is both impossible and unnecessary.

Dear Anil and others, much of the above discussions lingers on the definition of life. If one defines life as a general concept that applies to organisms, this leads to the question of "what is an organism?". Now the answer that an organisms is a 'living being' is not satisfactory, because it would create a circular reasoning, which is not acceptable from a philosophical point of view.

As a solution to this problem, I would suggest invoking the complexity ladder of the operator theory. Now organisms can be defined as 'particles' on the ladder from the level of the bacteria and up. To be regarded as a particle on the ladder a system must show particular structural and functional cyclic aspects, which I have named 'closures'. With this approach, life can be defined as the presence of the typical, level dependent closures in organisms. And living as the dynamic activity of organisms. And death as the loss of its closure when talking about an organism. This point of view offers a very generic way of defining life, which even is suitable to define "life as we don't know it".

More information about this approach can be found on the following website: http://the-operator-theory.wikispaces.com/Definition+of+life%2C+the+organism%2C+and+death

The most recent explanation of how a definition of life can be based on this way of reasoning can be found in my book "The Pursuit of Complexity".

So there may be a definition of life after all, but interestingly, it requires anchoring in a theory which is for a part based on information which is external to the field of biology. Which in turn may have been the reason why there have always been difficulties to come up with a definition from inside biology.

In many cases simple litmus tests can be used to examine existing definitions such as the "seven pillars of life" or any "working definition of life (e.g. of NASA)". For example use a frozen bacterium as a test and ask youself whether it does show metabolism, or whether it can reproduce now, or, worse, evolve (note that compliance with criteria for life, is something else than compliance with criteria for evolution, the latter being more demanding). Or use a strile born organism as a testcase and see whether it fits definitions requiring reproduction. As you may find out, it is very interesting, and educative, to test definitions this way.

Hope to have contributed to your considerations.

Gerard Jagers op Akkerhuis