Regarding:
> ...
>DNAunion:
>In mitochondria of extant cells, ATP will not form from ADP and inorganic
>phosphate. That is an uphill, non-spontaneous, thermodynamically disallowed
>process. But yet it does occur (in a sense, at least). That is, once you
>throw in excited electrons falling down complex electron transport chains,
>transmembrane proton gradients, proton-motive force moving protons through an
>ATPase, and rotation of the slotted "merry-go-round" in ATPase, then yeah, it
>can happen. But even so, it is still scientifically accurate to say -
>before, during, and after considering the mechanisms involved - that the
>reaction ADP + inorganic phosphate -> ATP is an uphill, non-spontaneous
>process: even though it happens in a roundabout way.
It's "downhill" if "you throw in excited electrons falling down complex
electron transport chains, transmembrane proton gradients, proton-motive
force moving protons through an ATPase, and rotation of the slotted
'merry-go-round' in ATPase" *and* you consider the composite fully
interacting process that results (among many other things) in the net
production of ATP. If you don't throw these things in, it *is* "uphill".
Of course, you would have a different situation then, wouldn't you?
Maybe you would have a dead cell, or at least a nonfunctioning
mitochondion. What is "downhill" in a functioning mitochondrion can
certainly be "uphill" in a non-functioning one, as they are different
systems which operate differently under different circumstances.
>To make it spontaneous,
>one would need to reformulate the reaction to something like ADP + inorganic
>phosphate + PMF + ATPase -> ATP. But note that establishing a PMF
>(proton-motive force) is a thermodynamically uphill process itself, as it
>requires pumping protons (hydrogen ions) against an existing gradient. And
>also the synthesis of the ATPase itself is an uphill process, requiring
>transcription and translation.
These prior reactions are only "uphill" when the protons are not pumped
and the ATPase is not transcribed and translated as they are when the
PMF *is* established and ATPase *is* synthesized. When the requisite
systems *are* in place so the cell actually functions normally, then all
of its reactions (no matter how complicated) *are* "downhill".
Otherwise, they wouldn't happen, as they would then be non-spontaneous.
When the cell is dead then some formerly "downhill" subprocesses become
"uphill", and some other formerly "uphill" subprocesses become
"downhill", since the fully interacting composite system is different in
the two cases.
...
>DNAunion: Agreed. But why do you feel uncomfortable in my using the term
>overcome in relation to an instance in which the influence that the tendency
>of one component, B, imposes on another component, A, is great enough that it
>causes A's behavior to change from its natural tendency itself?
Because I don't see either A or B as even having intrinsic individual
natural "tendencies" apart from the particular circumstances under which
they happen to find themselves.
David Bowman
David_Bowman@georgetowncollege.edu
This archive was generated by hypermail 2b29 : Mon Nov 13 2000 - 00:59:55 EST