Control Systems in the Living World - Building the Most Complex Structure on Earth - page 41

Hameroff. Protofilaments are composed of tubulin molecules in the form of tubulin
dimmers of α- and β-tubulin monomers. Tubulin dimers may be the basic computa-
tional units of MTs ( Penrose, 2003 ) that act as cellular automata for signal transmis-
sion ( Hameroff and Penrose, 1996 ). MTs propagate and process signals, and these
propagating signals appear to be relevant to the way that microtubules transport vari-
ous molecules alongside them, and to the various interconnections between neigh-
boring microtubules in the form of MAPs ( Penrose, 2003 ).
In another model, Georgiev proposes that dipoles of water molecules within
neurons break into dipole wave quanta that transmit information in water, influ-
encing microtubule tubulin “tails,” which transmit information along microtubules.
“Collisions of waves formed by the tubulin tails are suggested to act as a computa-
tional gate for the control of cytoskeletal processes” ( Georgiev, 2011 ), including the
determination of MAP attachment sites in microtubules, which in turn transmit the
output of the computations performed by the tubulin tails.
The Control System in Plants
The existence of an integrated control system in plants is not only a theoretical sine
qua non , but it is also an ex post factum conclusion to be drawn from the precise
control and regulation of plant reproduction, development, and growth. The high
order and certainty of the occurrence of these processes speak unmistakably to their
controlled and regulated nature.
Presently, however, knowledge about the plant control system is incomplete. We
know of the intracellular mechanisms of gene expression, and there is abundant
evidence on the extracellular signals, such as hormones, involved in gene expres-
sion and systemic networks. We can trace back the causal chain of gene expression
upward through epigenetic changes in DNA (methylation) or histones (acetylation/
deacetylation, etc.), consequential chromatine remodeling, and intracellular trans-
duction pathways up to the binding of cell receptors by these hormones. But we
do not know anything about causes behind the activation of hormonal pathways in
plants. We do not know yet what determines the coordinated activation of these hor-
mones and their pathways at the right time, at the right place.
The situation, in this regard, is by far more favorable in animals, where the
causal chain is known beyond just hormones that bind to membrane receptors. In
animals, the synthesis of hormones of the third tier (hormones produced by target
endocrine glands such as thyroid, adrenal, and genital glands) is triggered by hor-
mones of the second tier, secreted by the pituitary gland, such as thyroid-stimulating
hormone (TSH), adrenocorticotropic hormone (ACTH), and gonadotropins (follicle-
stimulating hormone (FSH) and luteinizing hormone (LH)). In turn, secretion of the
pituitary hormones is induced by hormonal signals that “release” hormones secreted
from a part of the brain called the hypothalamus, which represents the first tier of
hormones in the hierarchy of control in animals. Further up, the top of the control
hierarchy is occupied by higher centers of the brain.