Thesis-PDF - IAP/TU Wien
Thesis-PDF - IAP/TU Wien
Thesis-PDF - IAP/TU Wien
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
Figure 4.10: Preliminary model of the arrangement of rhodopsin-like proteins<br />
(colored green) in the photoreceptor. It is hypothesized that these are<br />
arranged in groups of three in a regular pattern across the layers. Each<br />
group would sit on a corner of the measured monoclinic unit cell shown in<br />
Fig. 4.9. a,b,c are the correspond edge lengths of the unit cell. That would<br />
lead to twelve molecules of rhodopsin per unit cell, about 2 ∗ 10 6 unit cells<br />
per crystal and therefore around 2.4 ∗ 10 7 molecules of rhodopsin in the<br />
photoreceptor. Diagram adapted from [100].<br />
4.3.4 Pellicle<br />
The pellicle defines the basic shape of the cell. Its role is vital to the organism as it<br />
must function as protection from the environment, yet cannot be fully impermeable<br />
as it must permit e.g. exchange of information or matter with the exterior as in<br />
sensory pathways or uptake of the vitamin B12. Additionally, euglenoid movement<br />
requires the strips of the pellicle to be highly flexible and articulate against each<br />
other. During my laboratory experience the cells have also shown excellent pressure<br />
resistance up to 100 bar and beyond.<br />
This sounds exciting enough for organic material, but still isn’t the whole<br />
story. There is strong evidence that the microtubuli within the strips (aligned in<br />
parallel) are responsible for the sliding of the strips against each other, meaning<br />
the pellicle changes its shape actively at the command of the cell! The fact that<br />
this protective shielding is self-assembling through means of special binding sites<br />
inside the plasmalemma membrane and binding proteins adds to this exceptional<br />
part of Euglena. ([101])<br />
If the cell is disrupted the pellicle can be seen dissociated along the striations<br />
into flat strips of material which have a thickened edge and a thinner flange.<br />
Electron microscopy sections clearly show how these strips interlock and how they<br />
52