Thesis-PDF - IAP/TU Wien

Figure 4.10: Preliminary model of the arrangement of rhodopsin-like proteins
(colored green) in the photoreceptor. It is hypothesized that these are
arranged in groups of three in a regular pattern across the layers. Each
group would sit on a corner of the measured monoclinic unit cell shown in
Fig. 4.9. a,b,c are the correspond edge lengths of the unit cell. That would
lead to twelve molecules of rhodopsin per unit cell, about 2 ∗ 10 6 unit cells
per crystal and therefore around 2.4 ∗ 10 7 molecules of rhodopsin in the
photoreceptor. Diagram adapted from [100].
4.3.4 Pellicle
The pellicle defines the basic shape of the cell. Its role is vital to the organism as it
must function as protection from the environment, yet cannot be fully impermeable
as it must permit e.g. exchange of information or matter with the exterior as in
sensory pathways or uptake of the vitamin B12. Additionally, euglenoid movement
requires the strips of the pellicle to be highly flexible and articulate against each
other. During my laboratory experience the cells have also shown excellent pressure
resistance up to 100 bar and beyond.
This sounds exciting enough for organic material, but still isn’t the whole
story. There is strong evidence that the microtubuli within the strips (aligned in
parallel) are responsible for the sliding of the strips against each other, meaning
the pellicle changes its shape actively at the command of the cell! The fact that
this protective shielding is self-assembling through means of special binding sites
inside the plasmalemma membrane and binding proteins adds to this exceptional
part of Euglena. ([101])
If the cell is disrupted the pellicle can be seen dissociated along the striations
into flat strips of material which have a thickened edge and a thinner flange.
Electron microscopy sections clearly show how these strips interlock and how they
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