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| Science Forum Index » Bio Evolution Forum » Separate and never at equilibrium (catabolic and... |
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| Tom Hendricks... |
 Posted: Sat Oct 10, 2009 6:54 pm |
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This supports these ideas
1. Catabolic and anabolic pathways are separate.
2. Catabolic and anabolic pathways are never at equilibrium.
Therefore they can evolve separately.
3. Change on either catabolic or anabolic pathways may put selection
pressure on the other pathway to better match and work together.
1 Catabolic and anabolic pathways are separate.
""Catabolic and anabolic pathways differ. If a metabolite is converted
to another metabolite by an exergonic process, free energy must be
supplied to convert the second metabolite back to the first. This
energetically "uphill" process requires a different pathway for at
least some of the reaction steps.
The existence of independent interconversion routes ... is an
important property of metabolic pathways because it allows independent
control of the two processes. If metabolite 2 is required by the cell,
it is necessary to 'turn off' the pathway from 2 to 1 while 'turning
on' the pathway from 1 to 2. Such independent control would be
impossible without different pathways."
2. Catabolic and anabolic pathways are never at equilibrium. Therefore
they can evolve separately.
"Living organisms, which take up nutrients, release waste products,
and generate work and heat, are open systems and therefore can never
be at equilibrium. They continuously ingest high-enthalpy, low-entropy
nutrients, which they convert to low - enthalpy, high - entropy waste
products. The free energy released in this process powers the cellular
activities that produce the high degree of organization characteristic
of life."
"Living organisms are thermodynamically open systems that tend to
maintain a steady state rather than reaching equilibrium. ...The flux
of intermediates through a metabolic pathway in a steady state is more
or less constant; that is, the rates of synthesis and breakdown of
each pathway intermediate maintain it at a constant concentration. a
steady state far from equilibrium is thermodynamically efficient,
because only a non equilibrium process can perform useful work. "
Whereas a system reaching equilibrium would work simultaneously, an
open system allows for the catabolic and anabolic pathways to work
independently of each other. One turns off while turning on the other
and / or they work separate pathways at the same or different times.
Because they work separately they can change separately or evolve
separately through natural selection on either side . There can be
variation in either pathway.
Example: "If glycogen synthesis and breakdown proceed
simultaneously , all that is achieved is the wasteful hydrolysis of
UTP. Glycogen metabolism must therefore be controlled according to
cellular needs."
3. Change on either catabolic or anabolic pathways may put selection
pressure on the other pathway to better match, and work together.
New or improved enzymes for example may quickly alter a catabolic
pathway; and may well put selection pressure on the anabolic pathway
to alter , match, or better regulate the other. Or vice versa.
Quote from Fundamentals of Biochemistry Voet, Voet, Pratt. |
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