Primordial sandwich
Encyclopedia
The concept of the primordial sandwich was proposed by the chemist
Günter Wächtershäuser
to describe the possible origins of the first cell membrane
s, and, therefore, the first cell.
According to the two main models of abiogenesis
, RNA world
and iron-sulfur world
, prebiotic processes existed before the development of the cell membrane. The difficulty with this idea, however, is that it is almost impossible to create a complex molecule such as RNA (or even its molecular precursor, pre-RNA) directly from simple organic molecules dissolved in a global ocean (Joyce, 1991), because without some mechanism to concentrate these organic molecules, they would be too dilute to generate the necessary chemical reaction
s to transform them from simple organic molecules into genuine prebiotic molecules.
To address this problem, Wächtershäuser proposed that concentration might occur by concentration upon ("adsorption
to") the surfaces of minerals. With the accumulation of enough amphipathic molecules (such as phospholipid
s), a bilayer
will self-organize, and any molecules caught inside will become the contents of a liposome
, and would be concentrated enough to allow chemical reactions to transform organic molecules into prebiotic molecules.
Although developed for his own iron-sulfur world model, the idea of the primordial sandwich has also been adopted by some adherents of the RNA world model.
Chemist
A chemist is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties such as density and acidity. Chemists carefully describe the properties they study in terms of quantities, with detail on the level of molecules and their component atoms...
Günter Wächtershäuser
Günter Wächtershäuser
Günter Wächtershäuser , a German chemist turned patent lawyer, is mainly known for his work on the origin of life, and in particular his iron-sulfur world theory, a theory that life on Earth had hydrothermal origins...
to describe the possible origins of the first cell membrane
Cell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
s, and, therefore, the first cell.
According to the two main models of abiogenesis
Abiogenesis
Abiogenesis or biopoesis is the study of how biological life arises from inorganic matter through natural processes, and the method by which life on Earth arose...
, RNA world
RNA world hypothesis
The RNA world hypothesis proposes that life based on ribonucleic acid pre-dates the current world of life based on deoxyribonucleic acid , RNA and proteins. RNA is able both to store genetic information, like DNA, and to catalyze chemical reactions, like an enzyme protein...
and iron-sulfur world
Iron-sulfur world theory
The iron-sulfur world theory is a set of proposals for the origin of life and the early evolution of life advanced by Günter Wächtershäuser, a Munich patent lawyer with a degree in chemistry who had been encouraged and supported by philosopher Karl R. Popper to publish his ideas. The theory...
, prebiotic processes existed before the development of the cell membrane. The difficulty with this idea, however, is that it is almost impossible to create a complex molecule such as RNA (or even its molecular precursor, pre-RNA) directly from simple organic molecules dissolved in a global ocean (Joyce, 1991), because without some mechanism to concentrate these organic molecules, they would be too dilute to generate the necessary chemical reaction
Chemical reaction
A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...
s to transform them from simple organic molecules into genuine prebiotic molecules.
To address this problem, Wächtershäuser proposed that concentration might occur by concentration upon ("adsorption
Adsorption
Adsorption is the adhesion of atoms, ions, biomolecules or molecules of gas, liquid, or dissolved solids to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. It differs from absorption, in which a fluid permeates or is dissolved by a liquid or solid...
to") the surfaces of minerals. With the accumulation of enough amphipathic molecules (such as phospholipid
Phospholipid
Phospholipids are a class of lipids that are a major component of all cell membranes as they can form lipid bilayers. Most phospholipids contain a diglyceride, a phosphate group, and a simple organic molecule such as choline; one exception to this rule is sphingomyelin, which is derived from...
s), a bilayer
Bilayer
A bilayer is a double layer of closely packed atoms or molecules. The properties of bilayers are studied in condensed matter physics, often in the context of semiconductor devices, where two distinct materials are united to form junctions ....
will self-organize, and any molecules caught inside will become the contents of a liposome
Liposome
Liposomes are artificially prepared vesicles made of lipid bilayer. Liposomes can be filled with drugs, and used to deliver drugs for cancer and other diseases. Liposomes are composite structures made of phospholipids and may contain small amounts of other molecules...
, and would be concentrated enough to allow chemical reactions to transform organic molecules into prebiotic molecules.
Although developed for his own iron-sulfur world model, the idea of the primordial sandwich has also been adopted by some adherents of the RNA world model.