ULTIMATE COMPUTING - Quantum Consciousness Studies

84 Cytoskeleton/Cytocomputer
Seifriz proposed the “brush heap theory” of interlacing fibers. He and others later
suggested that cytoplasmic fibers could exist in the brush heap form or could form
lateral associations by hydrogen bonding into paracrystalline aggregates, and that
switching between the two states accounted for cytoplasmic behavior observed in
living cells. We now know that subunits of the protein actin can polymerize in a
variety of forms including interlacing gels or filamentous bundles. Cytoplasmic
“gel” states occur due to crosslinking of actin filaments and other cytoskeletal
proteins, and can be converted to more aqueous “sol” states by calcium ions and
other factors.
Development of the electron microscope through the 1960’s initially did not
illuminate the substructure of cytoplasm. Portions of cells which were optically
empty by light microscopy persisted in being empty in electron micrographs. The
cell was perceived by many to be a “bag of watery enzymes.” However, in some
cases the fibrillar structures seen with light microscopy appeared as fine tubular
filaments with the electron microscope. They comprised the internal structure of
cilia, flagella, centrioles and basal bodies, and were prominent in the mitotic
apparatus of dividing cells. Tubular filaments were also frequently encountered in
protozoa, nucleated red blood cells and the dendrites of neurons. Ironically, the
fixative then used in electron microscopy, osmium tetroxide, had been dissolving
filamentous elements so that their presence was observed only sporadically. Like
the 19th century fixative induced coagulation which induced superfluous fibrillar
structures, the use of osmium tetroxide delayed recognition of the cytoskeleton.
Later, with the advent of glutaraldehyde fixation, delicate tubular structures were
found to be present in virtually all cell types and they came to be called
microtubules. Bundles of microtubules seen with the electron microscope
corresponded to birefringent fibers seen in living cells. Their ubiquity suggested
that they were the fibrillar substructure of cytoplasm previously predicted on
theoretical grounds. After some skepticism, microtubules became generally
accepted as “household organelles” in nearly all cells studied. Subsequent
characterization of actin, intermediate filaments, the microtrabecular lattice or
“ground substance,” and the structure of centrioles led to the recognition that cells
were comprised of dynamic networks of connecting filaments and brought the
cytoskeleton out of the closet.
5.2 Microtubules
Soifer (1986):
When microtubules are required by a cell for a particular function,
microtubules assemble in the appropriate part of the cell, with the
necessary orientation. As microtubules are no longer needed, they
depolymerize.
Essential functions within living cells ranging from single cell amoeba and
paramecium to neurons within earthworms and Nobel scholars are performed by
similar cytoskeletal structures. The most visible and widely studied cytoskeletal
elements are microtubules (MT), slender cylinders intimately involved in
important cell functions. As DNA is the common genetic data base containing
hereditary information, microtubules are real time executives of dynamic
activities within living cells.
5.2.1 Microtubule Structure and Function
Microtubules (MT) are hollow cylinders about 25 nanometers in diameter
whose walls are polymerized arrays of protein subunits. Their lengths may range
from tens of nanometers during early assembly, to possibly meters in nerve axons