ULTIMATE COMPUTING - Quantum Consciousness Studies

116 Cytoskeleton/Cytocomputer
removed still exhibit migration behavior. There is intelligence in the cytoplasm.
The cell has a driver’s license.
5.5.2 Bending Sidearms
Several important cytoplasmic movements occur due to bending of contractile
proteins attached along rigid cytoskeletal filaments. In muscle, arrays of parallel,
interdigitating “thin” filaments (actin) interact with “thick” filaments (myosin).
Tiny sidearms or crossbridges (“myosin heads”) attached to the myosin thick
filaments extend across a gap of about 13 nanometers and “cyclically row like
banks of tiny oars” to move the filaments relative to each other. The energy from
hydrolysis of ATP drives the conformational changes which causes the myosin
molecules to curl. The precise utilization of ATP hydrolysis energy to cause
contractility and other conformational changes remains poorly understood, but
will be discussed in Chapter 6.
Each myosin filament carries about 500 heads, each of which cycles about 5
times per second. There is some evidence of cooperativity in that once a myosin
head has detached, it is carried along by the action of other myosin heads along
the thick filament. The myosin head rowing is initiated and coordinated by waves
of calcium ion released from a reservoir (the sarcoplasmic reticulum) triggered by
membrane electrical activity. Rises in calcium ion causes an actin-bound
regulatory protein called troponin to shift its position and allow actin-myosin
ratcheting.
Many MT related activities generate force, locomotion and movement of
vesicles and other material; axoplasmic transport is one well studied example
(Lasek, 1981; Ochs, 1982). Parallel MT within axons are polarized with their fast
growing “plus-ends” distal from the cell body facing the synapse. Force
generating sidearms occur about every 16–18 nanometers along MT lengths.
These contractile crossbridges generate directional movement of material along
MT by undergoing a sequence of conformational changes involving attachment of
crossbridges to vesicles, ATP dependent force generation by the crossbridges, and
detachment of crossbridges from vesicles. Detachment occurs only at “plus” ends
near synapses. The process is similar to rowing of myosin heads to slide actin and
myosin filaments past each other and shorten muscle fibers. MT based dynein
activities, however, are far more variable, flexible, and interactive than the
repetitive nanoscale events in muscle. For example, in MT dependent axoplasmic
transport different material is simultaneously transported in the opposite direction,
from the synapse to the cell center. This “retrograde” axoplasmic transport is
thought to provide feedback to the protein synthesis machinery as to what
enzymes or material are required, and/or to allow “recycling” of some molecules
(Figure 5.25).
Robert Allen (1985) was among the first to suspect that MT and MAPS
served as intracellular conveyor belts. He and his colleagues studied isolated MT
and MT fragments which, with .available biochemical energy in the form of ATP,
“glide” along glass cover slips at velocities of 150 to 450 nanometers per second.
The velocity is independent of MT fragment length, occurs essentially in a
straight path, and is in the direction of retrograde axoplasmic transport. The
straight paths of gliding MT segments suggest that the force generating enzymes
are deployed in linear, rather than helical paths along the MT, and that the stroke
that causes gliding is parallel to the MT with a spacing interval of about 17
nanometers. Reducing the available ATP concentration slows the gliding speed
significantly, but does not affect the number or behavior of gliding MT. Gliding
MT almost never interact when they cross paths, and when the forward progress
of a gliding MT is blocked by an obstacle, it “fishtails” slowly from side to side