Re: Flagellum linkage

On Sat, 30 Jun 2007 09:22:31 -0500, Dick <remdickhm@xxxxxxxxxxxxx>
wrote:

I am very impressed with various serious discussions about evolution
by linkage if proteins with pre-existing functions. I have enjoyed the
give and take. I have no technical ability so I will talk with the
car analogy in mind. I am unable to decipher the linking of
pre-existing functional proteins with the transition from a bacteria
to the flagellum.

It seems to me the idea of linking pre-existing functions such as a
motor, drive shaft and wheels together is very over simplified.
Accepting that the whip, pore, drive shaft and motor functions are
available to the basic bacteria, I cannot understand how these
functions can join in any useful manner.

A motor is useless unless it is stable, has a functioning control
mechanism, which requires goal directed instructions, and fuel source.

A pore originally serves as a passage for specific molecular movement,
in or our of the cell membrane. A bearing needs to support a load and
dissipate heat (energy).

A shaft connects things and adapts to the bearing (pore) support.

A whip that originated to be fixed to the membrane would not be well
suited to rotary forces.

Finally, each of these functions need linking surfaces that recognize
molecular shapes and electrical charges unique to the selected
functional proteins.

How many unique and at least neutral mutations would such
transformations require?

"I cannot imagine" such serendipity. Can someone explain to me, in
non technical vocabulary how such functions might have been formed
(what survivable functions), and how they might have accidentally
joined together?


There is a well argued model of the origin of the bacterial flagellum
in the literature; I will let others point you to it because I don't
have the citation at my fingertips.

There are some misconceptions in your argument. First, you say "A
motor is useless unless it is stable, has a functioning control
mechanism, which requires goal directed instructions, and fuel
source." The motor need not be terribly stable; an episodic one that
resulting in some movement might well be favorable over the complete
lack of a motor. Again, the control need be very primitive and
without "goal directed instruction". Merely "turn on" under some
conditions and "turn off" under others. Turning on when energy is low
and off when it is high results in undirected movement when food is
not available and stasis when it is. Such patterns are well known in
many protozoans and even in multicellular animals and results in
"moving to new food sources" when supplies in the immediate area are
exhausted but remaining in one area as long as the food supply is
adequate. No directed movement is required.

Things of sub-microscopic dimension work rather differently from
human-sized objects. The bearing does not support any substantial
load, nor is there any problem of friction or heat dissipation.
Because of the extremely high Reynold's number at small dimensions,
effective locomotion is obtained simple by sticking something out the
side of a cell and wiggling it. Cell are well capable of producing
long thin filaments, of producing pores (holes) in the membrane, and
inserting protein structures into the membrane. There are innumerable
examples of bacterial cell function that involves those steps and they
are easily accomplished by physical chemical manipulations. Producing
a filament and sticking it into a pore in the membrane is no great
stretch. Cells also have internal motile mechanisms: this is a
necessary part of basic cell physiology. So making the filament
motile by one means or another is also a reasonable development. The
highly elaborate modern bacterial flagellum could have developed much
later as refinements from a very primitive albeit only slightly
functional start.

.

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