It's not my definition, Ami; keep your facts straight. It is the working
definition accepted by biologists and biochemists in general. You'll find
it, in one form or another, in virtually any biology or biochemistry
textbook, though rarely as a single declarative sentence like this. J.
David Rawn in his textbook defines life as an organized metabolic system
consisting of interacting biomolecules. You won't find that exact phrase
anywhere in his book, but if you read his introduction you get that distinct
impression. Robert H. Abeles, Perry A. Frey and William P. Jencks place
more emphasis on the interaction of biomolecules in their textbook, but
their definition of life is much the same. In his textbook, Geoffrey M.
Cooper treats all of cell biology as one huge dynamic molecular system, and
in his brief discussion of abiogenesis clearly links life to this same
dynamic molecular system. In his own textbook, Albert L. Lehninger defines
life with a single statement that sounds very much like mine.
So again, it is not "my definition", nor is my way of expressing it
particularly unique among my fellow biochemists.
>It is simply a
>"metabolic system which uses polymeric catalysts to breakdown biomolecules
>for energy and raw materials, which it then uses to create new structures
>(again using polymeric catalysts), " I have not been convinced that it has
>any contribution other than the value of being able to claim that life has
That's because you are not familiar with the scientific literature. Both
Cooper and Lehninger make it the basis of their discussions of abiogenesis;
Lehninger even gives a few examples of living systems that by that time
(1970) had already been created in the laboratory. Cooper's description is
briefer, but it is clear that he accepted the creation of life in the lab as
a verifiable fact.
>...(Hrm, by an intellegent agency, I might add using, of course,
>natural processes such as self assembly) from simple chemicals. This does
>very little, IMO, for the theory of abiogenesis without intellegent
Which is entirely irrelevent. If it was impossible to create life from
simple chemicals, no amount of manipulation of natural processes would have
achieved any results, not even the creation of simple biomolecules. The
fact that biomolecules, catalytic polymeric macromolecules and simple
integrated metabolic systems, plus certain primitive replicating systems,
can be quite easily made in labs by the proper manipulation of the
physiochemical forces simple means that nature could have done it also. Or
are you suggesting that the scientists miraculously created life through
sheer force of will?
>Now, if one wants to use the above definition as that for life processes,
>then that is okay. But that definition does nothing to advance the cause
>explaining how we got from simple chemicals to the simplest modern cells
I have already admitted to Ami that no one has yet created a **modern**
cell. But we have created the precursors to modern cells: primitive cells
that can metabolize and replicate without genetic material. From there we
need only explain how genetic material was first incorporated, and then the
modern cell would have simply evolved from that intermediate. Ami's
requirement is too restrictive to the basic question: has life been created
in modern laboratories. The answer is yes, though it still has a long way
yet to become a modern living organism.
>Or,similarly, the most recent common ancestor all life now on
>earth shares (which was probably simpler still). This definition of life
>does not carry with it the real attributes of life such as reproduction,
>information and even evolution.
That's because reproduction, information and (biotic) evolution are the
results of life, not the cause of life. You have to have a living system
before you can have reproduction, information or (biotic) evolution. Ami
never seemed able to grasp that simple truth.
>This is the second time that Kevin has made this claim. He did not
>it to my satisfaction a couple of weeks ago, either publicly or in the
>private exchange which he moved the discussion to.
She didn't give me the chance. She kept fighting me tooth and nail on the
basic stuff that I never got a chance to provide any validation of the more
advanced stuff. Unless she understood the basic stuff, she would never
understand the validation, but she didn't appreciate that. I kept begging
her to simply listen with an open mind and to take my word for it for the
time being and she kept refusing. So I had to end it. It sort of reminded
me of a time in graduate school when I was trying to tutor an undergraduate
on enzymes. She kept demanding proof that enzymes were catalysts; I kept
trying to explain that that was a basic concept she had to accept and that
all would become clear once I was able to move on to discussing kinetics and
specific mechanisms, but she wouldn't budge. In the end she fluncked
biochemistry because she never could accept that enzymes were catalysts.
Now, I'm not the best teacher in the world, but other tutors told me they
had the same problem with her. Even her professor couldn't get through to
her. There was nothing anyone could do, since the concept of enzymes as
peptiditic catalysts is a basic definition that even most textbooks do not
try to defend or support. The only way to give her the proof she needed was
to explain about topics she didn't have enough training to understand.
Neither could I prove to Ami that the definition of life I was using was
crucial to understanding abiogenesis without discussing topics that are
years ahead of her yet in college. There was simply nothing I could do if
she wouldn't take my word that what I was saying was true.
Kevin L. O'Brien