Self-reproduction of vesicles

It has already been discussed in Chapters 7 (self-reproduction) and 8 (autopoiesis) that, under certain conditions, vesicles are capable of undergoing an autocatalytic process of self-reproduction. This is a novel, dynamic aspect of the reactivity of such aggregates, which clearly has relevance for the field of the origin of life. 

Vesicle self-reproduction described until now can be defined as autopoietic, since growth and eventually reproduction comes from within the structure boundary. One can also induce growth and division of fatty acid vesicles by adding fresh surfactant from the outside, for example as a micellar solution at high alkaline pH. 

Let us consider the mechanism. When monomeric oleate or oleate micelles are added to a solution containing oleate vesicles, two limiting situations may occur. 

For example, if fresh POPC from a methanol solution is added to a POPC hposome solution, there will be an immediate formation of fresh liposomes. In fact, the cmc in this case is of the order of 10 ° in favor of the aggregates over the free monomers, and the rate of formation is correspondingly extremely high. Thus, we are in the presence of an independent self-assembly mechanism. 

In contrast to this is the addition of oleate surfactant - in the form of micelles or free monomer - to oleate or to POPC vesicles. In this case, the ratio of the two competitive rates is such that a considerable binding of the added fresh surfactant to the pre-existing vesicles takes place. The efficient uptake of oleate molecules by POPC liposomes (Lonchin et al., 1999) as well as to oleate vesicles (Blochiger et al., 1998) is well documented in the literature. 

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We have also learned that self-replication is not a prerogative only of nucleic acids, but it can be shared by different kinds of chemical families see the formose reaction, the self-replicating peptides, and the self-reproducing micelles and vesicles. The list should include the cellular automata and the corresponding devices of artificial life. Self-reproduction of vesicles and liposomes is important because it represents a model for cell reproduction. 

In the case of Walde et al. (1994a) the synthesis of poly(A) - which can be viewed as a simple form of RNA - proceeded simultaneously with the self-reproduction of vesicles, thus providing a core and shell reproduction, as schematically illustrated in Figure 10.3. 

Polynucleotides phosphorilase producing poly(A) from ADP 2. poly(A) is produced inside simultaneously with the (uncoupled) self-reproduction of vesicles. 

Type I system. Self-reproduction of vesicles. The starting point is the concept of vesicle self-reproduction. This important vesicle pattern was observed for the first time in 1994 and thoroughly studied till recently, being one of the most important reactive behaviour of fatty acid vesicles. Figure 17.8a shows the experimental model for autopoietic... 

Stano P, Luisi PL (2010) Achievements and open questions in the self-reproduction of vesicles and synthetic minimal cells. Chem Commun 46 3639-3653... 

In general, the mechanism of self-reproduction of micelles and vesicles can be considered an autopoietic mechanism, since growth and eventually division comes from within the structure itself. This point will be considered again in Chapter 8, on autopoiesis, where the mechanism of the self-reproduction process will also be discussed. 

In the various reviews on self-reproduction in recent years, practically no mention is made of such micelles or vesicle systems. The reason lies most prohahly in the bias of classic hiochemical literature, according to which self-replication is tantamount to nucleic acid systems lacking this are therefore deemed not to he relevant. In this particular regard, it is argued that self-reproduction of micelles and vesicles proceeds without transmission of information. 

The term chemical autopoiesis indicates the experimental implementation of autopoiesis in the chemistry laboratory. The most well known of these processes is the self-reproduction of micelles and vesicles. This has been discussed in the previous chapter, where the original idea of Francisco Varela and myself was to work with bounded systems that would produce their own components due to an internal reaction, respecting the scheme illustrated in Figure 8.3. We came up with the idea of using reverse micelles (refer back to Figure 7.13) with two reagents. 

When the velocities of the two reactions are numerically equal, the system is in homeostasis, a dynamic equilibrium that does not modify the identity of the unit. Conversely, when the velocity of the building-up reaction Vp is larger than the opposite one, growth and eventually self-reproduction of the vesicles can be measured and if instead Vp is smaller than uj, there is destruction of the unit. 

Reverse micelles are the first compartment structures for which the phenomenon of micelle self-reproduction has been described (Bachman et al., 1990 1991). This experimental work was a follow up of a theoretical study by Varela and Luisi (Luisi and Varela, 1990), and is it this that eventually brought to light the self-reproduction of aqueous micelles and vesicles. This has been covered already in Chapter 7, on the chemistry of self-reproduction. 

Vesicles can self-reproduce, however it is argued that there is no information content passing from one generation to the next. What do you think is information really so important for self-reproduction of early protocells ... 

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

Morigaki, K., Dallavalle, S., Walde, P, Colonna, S., and Luisi, P. L. (1997). Autopoietic self-reproduction of chiral fatty acid vesicles. /. Am. Chem. Soc., 119, 292-301. 

Light-microscopic inveshgations of the autocatalytic self-reproduction of giant vesicles. Journal of the American Chemical Society, 117 (4), 1435-1436. 

The main point of this chapter is to show that supramolecular aggregates can play an important role in the early history of the origin of life. The main driving force in all processes we have illustrated is the hydrophobic interaction—this is responsible for the self-assembly of vesicles, for the binding of hydrophobic substances to the vesicle membranes and the corresponding autocatalytic self-reproduction of micelles and vesicles, as well as for the corresponding chemical events of polymerization. Since the hydrophobic forces take place generally spontaneously and with... 

Wick, R., Walde, R, Luisi P. L. (1995). Light microscopic investigations of the autocat-alytic self-reproduction of giant vesicles, J. Am. Chem. Soc., 117 1435. 

Walde, P. Wick, R. Fresta, M. Mangone, A. Luisi, P.L. Autopoietic self-reproduction of fatty acid vesicles. J. Am. Chem. Soc. 1994, 116, 11649-11654. 

So far, only the self-replication mechanisms of linear molecules have been described it is now time to consider closed spherical structures, such as micelles and vesicles. Here, the term self-reproduction will be used rather than self-replication, because, as it will be seen, the population increase is generally based on statistical processes. The subject of micelles and vesicles self-reproduction is dealt with in other chapters in this book a certain degree of repetition and/or mis-match is unavoidable. 

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