Vesicles model

Jay, D. and Gilbert, W. (1987). Basic protein enhances the encapsulation of DNA into lipid vesicles model for the formation of primordial cells. Proc. Natl. Acad. Sci. 

Self-reproduction of micelles and vesicles models for the mechanisms of life from the perspective of compartmented chemistry. Adv. Chem. Phys., 92,425-38. 

FIGURE 7.25. Chemical structure of the penta-substituted fullerene potassium salt. In the present work, only the compound with R = CgHs has been studied. A bilayer vesicle model, consisting of Noaia = 6693 molecules in an outer shell of radius i outer = 517.6 nm plus AIjnner = 5973 molecules in an inner shell of radius Sinner = 16.7 nm. A sector has been cut out for clarity. The hydrophobic fullerene bodies are shown in green, the hydrophilic charged cyclopentadienide regions are in blue, and the five substituents are schematically represented as yellow sticks. 

Fig. 9 One of the vesicle models (as depicted by the SCM). Different templates (labelled by open and closed circles) contribute to the well being of the compartments (protocells) in that they catalyse steps of metabolism, for example. During protocell growth (-- ) templates replicate at differential expected rates, but stochastically. Upon division (- ) there is chance assortment of templates into offspring compartments. Stochastic replication and reassortment generate variation among protocells, on which natural selection at the compartment level can act and oppose to (correct) internal deterioration due to within-cell competition...

The consequences of imperfect replication in vesicle models are somewhat puzzling [85,90]. For small mutation rates an increased level of polyploidy favours the persistence of protocell lineages since the random loss of essential genes after fission is attenuated. However, for large mutation rates the situation is reversed, resulting in that those lineages with low levels of polyploidy... 

Fig. 6 Vesicle model proposed by Steudel for sulfur globules excreted by Ac. ferrooxi-dans. Vesicles are composed of long chain polythionates ( 03S-Sn-S03 ) in which small amounts of sulfur rings can be present (after [24])...

It should be noted that polythionates are only stable at low pH [33] and it is therefore unlikely that the polythionate vesicle model is appHcable to sulfur globules produced by bacteria growing at another pH Aan the acidic conditions at which Ac. ferrooxidans grows [5] (see Fig. 6). 

We have previously mentioned that lipids make part of the membrane architecture, which has the typical bilayer arrangement due to the phospholipid supramo-lecular organization. This leads to biological consequences - the composition of fatty acid residues with saturated and unsaturated hydrocarbon chains is crucial to regulate membrane properties, maintaining the best balance for cellular functioning and also survival. Vesicle models made of phosphatidylcholines with saturated and unsaturated fatty acid residues are useful for studies of permeability and fluidity. Several studies have compared the effects of saturated, cis and trans unsaturated residues. An example is given in Fig. 6.4 for vesicles made up of different phospholipid compositions. 

Artificial phospholipid vesicles (liposomes) are used to transport vaccines, drugs, enzymes or other substances to target cells or organs. They also make excellent model systems for studying biological ion transport across cell membranes. The vesicles, which are several hundred nanometres in diameter, do not suffer from interference from residual natural ion-channel peptides or ionophores, unlike purified natural cells. For example, the synthetic heptapeptide 5.23 forms pores that promote chloride efflux in vesicle models. Similarly, the ion-pair receptor 2.108 can ferry NaCl from vesicles as an ion-pair ionophore (see Chapter 2, Section 2.6.2), while the hydraphile 5.24 has been shown to transport Na using Na NMR spectroscopy through the bilayer walls of a vesicle model system. 

A second challenge to the vesicle model refers to the sorting capacity of the endomembrane system since it would predict that structurally related compounds destined to travel to the vacuole or the extracellular space need to be sorted in the ER or downstream of this compartment in a manner comparable to vacuolar or secretory proteins. In consequence, either specific receptors recognizing the different phytochemicals must be postulated or the synthesis of metabolites that need to be distributed to distinct compartments takes place on spatially separated complexes. Thus, the interface between phenolic biosynthesis, including distinct metabolons, and the loading of end products into primary transport vesicles, most probably at the ER surface, requires and surely will attract much research interest in the future. 

Figure 9.13 A bilayer vesicle model, hydrophobic flillerene bodies are shown in...

The data were fitted using a single thin shell vesicles model with radius R [67] and a Gaussian size distribution f x) to take into account polydispersity, according to the relation... 

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