1,925 research outputs found
Unicellular algal growth: A biomechanical approach to cell wall dynamics
We present a model for unicellular algal growth as motivated by several
experiments implicating the importance of calcium ions and ``loosening''
enzymes in morphogenesis. A growing cell at rest in a diffusive calcium
solution is viewed as an elastic shell on short timescales. For a given turgor
pressure, we calculate the stressed shapes of the wall elements whose elastic
properties are determined by Young's modulus and the thickness of the wall. The
local enzyme concentration then determines the rate at which the unstressed
shape of a wall element relaxes toward its stressed shape. The local wall
thickness is calculated from the calcium-mediated addition of material and
thinning due to elongation. We use this model to calculate growth rates for
small perturbations to a circular cell. We find an instability related to
modulations of the wall thickness, leading to growth rates which peak at a
finite wave number.Comment: 5 pages, 2 embedded figure
Properties of Cooperatively Induced Phases in Sensing Models
A large number of eukaryotic cells are able to directly detect external
chemical gradients with great accuracy and the ultimate limit to their
sensitivity has been a topic of debate for many years. Previous work has been
done to understand many aspects of this process but little attention has been
paid to the possibility of emergent sensing states. Here we examine how
cooperation between sensors existing in a two dimensional network, as they do
on the cell's surface, can both enhance and fundamentally alter the response of
the cell to a spatially varying signal. We show that weakly interacting sensors
linearly amplify the sensors response to an external gradient while a network
of strongly interacting sensors form a collective non-linear response with two
separate domains of active and inactive sensors forming what have called a
"1/2-state" . In our analysis we examine the cell's ability to sense the
direction of a signal and pay special attention to the substantially different
behavior realized in the strongly interacting regime.Comment: 8 pages, 5 figure
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