Vesicular shape

Amphipilic polypeptides that are synthesized with appropriate ratios of hydrophilic to hydrophobic blocks can form ordered vesicular shapes. Although many polypeptides can self-assemble into vesicles when simply dissolved in the correct solvent, others require more processing steps. This section provides an overview of the techniques that have been developed to process various polypeptide and polypeptide hybrid systems into vesicles. 

Vesicular shape and surface morphology can be assessed by transmission electron microscopy (TEM) with an accelerating voltage of 100 kV using standard techniques. 

Figure 5.5.3 The tetrabixinatoporphyrin produces stiff, isolable vesicles. Upon irradiation with visible light the bixin chromophores bleach out quantitatively and totally insoluble polymers of vesicular shape are formed. The polymer structure given is hypothetical.

Amphiphilic molecules such as surfactants and block copolymers containing hydrophobic (water-insoluble) and hydrophilic (water-soluble) parts, serve as simple synthetic model systems for understanding self-assembly. Micellization is a common self-assembly process whereby amphiphilic molecules spontaneously aggregate into various nanostructures that are usually of spherical, ellipsoidal, cylindrical, or vesicular shapes [1, 2]. These processes usually occur in selective solvents, i.e., solvents that are good for one part but poor for the other. Here, self-assembly is primarily driven by the incompatibility of the insoluble (hydrophobic or more generally solvophobic ) part with water or other solvents, and is mainly counteracted by repulsions or unfavorable configurations experienced in the swollen corona of the resulting micelles. 

In many cases, under changing experimental conditions, water-containing reversed micelles evolve, exhibiting a wide range of shapes such as disks, rods, lamellas, and reverse-vesicular aggregates [15,107,108], Nickel and copper bis(2-ethylhexyl) sulfosucci-nate and sodium bis(2-ethylhexyl) phosphate, for example, form rod-shaped droplets at low water contents that convert to more spherical aggregates as the water content is increased [23,92,109,110],... 

The cytosol is the fluid compartment of the cell and contains the enzymes responsible for cellular metabolism together with free ribosomes concerned with local protein synthesis. In addition to these structures which are common to all cell types, the neuron also contains specific organelles which are unique to the nervous system. For example, the neuronal skeleton is responsible for monitoring the shape of the neuron. This is composed of several fibrous proteins that strengthen the axonal process and provide a structure for the location of specific membrane proteins. The axonal cytoskeleton has been divided into the internal cytoskeleton, which consists of microtubules linked to filaments along the length of the axon, which provides a track for the movement of vesicular material by fast axonal transport, and the cortical cytoskeleton. 

Experiments have shown that, in most cases, such as for SDS, the initially spherical-shaped micelles may be influenced to grow under into larger aggregates (disclike, cylindrical, lamellar, vesicular) (Figure 3.11). 

Large viruses of 80 -100 nm diameter bearing 8-10 spikes at the vertices of the icosahedra cause influen-za 509,510 mumps, measles, and related diseases. The internal structure must be complex. Only 1% of the virus is RNA, and that consists of several relatively small pieces. These are negative strand viruses whose RNA is of the opposite polarity to the mRNA. The latter must be formed by transcription from the negative strand. The viruses carry their own RNA polymerase for this purpose. Of even more complex structure are the bullet-shaped rhabdoviruses which cause rabies and vesicular stomatitis.511 The diameter of these viruses is 65-90 nm and the length 120-500... 

Synaptic-like microvesicles (SLMVs) represent the best characterized vesicular organelles in astrocytes. They strongly resemble SVs of nerve terminals in size and shape (Bergersen and Gundersen, 2008 Bezzi et al., 2004 Crippa et al., 2006 ... 

Neurons cannot synthesise proteins along the axon and are particularly dependent on vesicular transport to provide them. Many neurodegenerative disorders show examples of defects in the cytoskeletal tracts, which sustain neuronal shape and trafflcking, or defects in the motors, which provide energy for vesicle/organelle movement, including mitochondria. 

As already mentioned, to rationalize the shape and size of the aggregate is difficult and also the number of studies on the relationship between structure and the physicochemical properties of these luminescent metalloaggregates remain limited so far (50,104,114,115), and mostly dealing with spherical micelles, even though few vesicular systems have been also reported (116). In addition, these aggregates have been studied mainly in aqueous solutions, while there are only few known metallosurfactants which aggregate in organic solvents (116,117). 

We shall deal with ionic and zwitterionic amphiphiles. These can take on a confusing variety of different shapes and sizes some aggregate into small spherical or globular micelles, others appear to form long cylindrical micelles, while others coalesce spontaneously into vesicular or lamellar bilayers. 

The existence of a curved conformation associated with the action potential is supported by the fact that the ion influx at the spike will induce an increased average wedge-shape of the molecules, due to electrostatic screening of the lateral repulsion of phosphatidylserine molecules. Furthermore a conformation associated with the spike would directly relate action potential propagation to the mass-cooperative vesicular fusion, involved in the chemical signal transfer by transmitter molecules at the pre-synaptic membrane. Experimental support for this concept has been recently reported [39]. This well-controlled fusion process of numerous "vesicles" with the presynaptic membrane must take place as a phase transition. The... 

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