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The difference between living and dead matter?


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#1 Transdecimal

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Posted 17 March 2008 - 02:21 PM

How does one explain, using scientific terminology, the difference between living and non-living material that has the same molecular structure?

If you (or a computer) were to analyse a bacterium at the molecular level, how could you tell the difference between a living bacterium and a dead one?

Obviously there is a way because there is a difference, but what is this way?
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#2 thedarkshade

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Posted 18 March 2008 - 07:49 PM

Living "matter" changes, always tries to fit where it is located, seeks for food as a source of energy in a way or another, gets developed, reproduces and then dies, decomposes and becomes non-living.

A very rough idea about live and dead, but that's mainly it!
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#3 Eureko

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Posted 18 March 2008 - 11:25 PM

Maybe could we say that living matter suffer process by itself and dead one does not? Thatīs it: reproduces, grows, gets feed... etc. Well, I just donīt know.
I donīt know the answer but Iīd like us to discuss about it so letīs see what could we find.
I have always wondered whatīs exactly the difference between a dead body (I think about a human one) and a living one, if, in both cases they have exactly the same structure... whatīs the key to differ between the one living and the other dead, what makes it one to be one way and the other the opposite...
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#4 Transdecimal

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Posted 19 March 2008 - 01:58 AM

But isn't that all at the macroscopic level (if that's the right word)? Growing, feeding, reproducing etc.

I'm thinking more about the molecular structure of the living matter...
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#5 Mr Skeptic

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Posted 19 March 2008 - 02:42 AM

Much of the structure of living things is protein crystals. The shapes and binding locations of the proteins mostly determine the shape of the structures. Living things have a way to get energy from the environment and to drive unfavorable chemical reactions with it. There are enzymes that greatly facilitate chemical reactions, and "molecular machines" which use chemical energy to drive thermodynamically unfavorable actions. The enzymes have feedback regulation loops.
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#6 Eureko

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Posted 19 March 2008 - 04:34 PM

And donīt forget the accumulation of dioxins and free radicals that might cause natural deaths of organisms...
But, if we take an organism, and hypothetic one, I wonder (also at molecular level) whatīs the difference in the just two consecutive moments that differ from the living to the dead organism...
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#7 lucaspa

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Posted 25 March 2008 - 05:04 PM

How does one explain, using scientific terminology, the difference between living and non-living material that has the same molecular structure?

If you (or a computer) were to analyse a bacterium at the molecular level, how could you tell the difference between a living bacterium and a dead one?

Obviously there is a way because there is a difference, but what is this way?


It's easy. Remember that to be alive the entity has to have all 4 of the following characteristics:
1. Metabolism (both anabolism and catabolism)
2. Growth
3. Response to stimuli
4. Reproduction.

It's very easy to see that a dead bacterium has no metabolism.

For multicellular organisms, the old saying "poke it with a stick" is testing #3. If there is no response to stimuli and no metabolism, the entity is not alive, even tho it might once have been.

Much of the structure of living things is protein crystals.


Proteins do not exist as "crystals". Proteins can sometimes be "crystallized" in order to do x-ray diffraction. But the reason so many proteins have NOT been analyzed by x-ray diffraction is that they cannot be crystallized.

Living things have a way to get energy from the environment and to drive unfavorable chemical reactions with it.


Called "anabolism". However, it's not enough to "drive unfavorable chemical reactions". For anabolism you need to use the energy to make the molecules of the living organism. Yes, those reactions are "unfavorable", but they are very specific unfavorable reactions.

But, if we take an organism, and hypothetic one, I wonder (also at molecular level) whatīs the difference in the just two consecutive moments that differ from the living to the dead organism...


If you have a multicelled organism, there is no "two consecutive moments" between life and death. There is a continuum. For instance, an organism can be brain dead, not breathing, and no heartbeat, but most of the cells will be alive. That's how we do cell harvest.

In microorganisms, the causes of death have been studied in some cases. In most cases, it's when metabolism ceases. That can have a number of causes.

1. With treatment with penicillin, the cell wall breaks and the contents of the bacteria leak out. The cellular components become separated and metabolism ceases.
2. If we treat bacteria with ethanol or disinfectant, then the proteins are denatured and precipitated. Metabolism ceases.
3. In the case of accumulating oxidative damage, first the DNA stops coding for functional proteins, then the proteins and lipids that are oxidized stop functioning. Metabolism ceases.

See a pattern here?
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#8 abateNth

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Posted 28 March 2008 - 09:58 AM

How does one explain, using scientific terminology, the difference between living and non-living material that has the same molecular structure?

If you (or a computer) were to analyse a bacterium at the molecular level, how could you tell the difference between a living bacterium and a dead one?

Obviously there is a way because there is a difference, but what is this way?


For many forms, it's the rate of decomposition. Which is relative to the organism in the way it breaks down. Certain compounds arise, and are not removed from the bio-structure. All things living decay; it's when the rate becomes accelerated, with no system of removal of the decay.
In say, bacteria, depending on the type, you'd look for something that was toxic within the system that normally is broken down. When it amasses to a level it is terminal to the colony, then you know they no longer are viable.
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#9 Mr Skeptic

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Posted 29 March 2008 - 05:10 AM

Proteins do not exist as "crystals". Proteins can sometimes be "crystallized" in order to do x-ray diffraction. But the reason so many proteins have NOT been analyzed by x-ray diffraction is that they cannot be crystallized.


I was reading about recent research concerning self-organizing cell structures. Some, for example the flagella, are made of protein units in regular arrangements. Some require a seed to get started. They exist in equilibrium, with the rate of units falling off equal to the rate of units getting replaced. The clever thing about that is that it doesn't require guidance to build or repair itself, only free proteins.

Haven't heard anyone call it crystals before, but it fits the definition.
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