Biology Reference
In-Depth Information
movement has been limited by the deformation of the previously leading microtu-
bules. It is notable that the time that the secretory apparatus associated with the
lymphocyte centrosome spends next to the given target is determined by the elastic-
ity of the cytoskeleton. It is equally notable that the movement of the cell body to
the other synapse is a mechanical consequence of its previous movement to the
synapse where it is presently found.
In summary, purely deterministic and conceptually simple biomechanical mod-
els are capable of exhibiting complex, life-like cell body movements and deforma-
tions. The computational results demonstrate that the origin of the strikingly animate
“wandering of aim” in T-killer cells of the immune system need not be sought in
stochastic dynamics of individual molecules, or in indecision that might be exhib-
ited by complex information processing in the T cell, or in indeterminate changes in
the signaling input from the target cells. Instead, the rigorous numerical demonstra-
tion that a purely deterministic mechanical explanation exists for one of the most
animate behaviors exhibited by cells suggests that similar explanations and support-
ing experimental evidence can be sought for other types of cell behavior that appear
far from mechanistic.
Complex movements of the cell body within the cell boundary, such as those
reviewed in the introduction to this section, are likely to have similar physical basis.
Movements that are evidently oscillatory (albeit multiperiodic) can arise, in the
light of the present theory, from the flexure of the confined cell body cytoskeleton
and the tangential nature of forces exerted on it by the molecular motors of the
boundary. Other complex movements which may not appear periodic may nonethe-
less be decomposed into a series of oscillations with different frequencies. More
broadly, the relation of the cyclical movement of the confined cell body to one that
is irreversible, as discussed in this section, and the asymmetric nature of the stable
static cell body conformations, which was the subject of the previous sections, dem-
onstrate intimate continuity of the most fundamental systems-biomechanical phe-
nomena treated in this topic.
It is hoped that the systems-biomechanical line of investigation into the emer-
gence of life-like complex form and movement on the cellular level will be contin-
ued, as it has potential to illuminate the understudied role of sufficiently complex
supramolecular mechanics in the physics of living matter. It is not inconceivable in
the light of the preliminary results discussed here that the comparatively simple
mechanical organization of the living matter on the cellular level, when viewed
through the prism of adequately sophisticated quantitative systems theory, may prove
to be causa prima for the complex form and movement that exemplify life. Indeed,
the latter are mechanical phenomena (equilibria and disequilibria), and emerge on
the cellular level. What had been lacking until recently was application of rigorous
quantitative systems methods to cell mechanics. The maturing of the systems
approach to biology in general, and the accessibility of adequate computing power to
analyze models without simplification for the sake of computability have created the
preconditions for a radically new methodology. Its application to cell biomechanics
is opening the path to truly mechanistic understanding of the cellular form and move-
ment, whose self-organization demarcates the living from the nonliving matter.
