Microsphere

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Not to be confused with Glass microsphere.

This article largely refers to microspheres or protein protocells as small spherical units postulated by some scientists as a key stage in the origin of life. The term microsphere is otherwise widely being used in various areas, such as, materials and pharmaceutical sciences, for spherical particles composed of various natural and synthetic materials with diameters in the micrometer range.

In 1953, Stanley Miller and Harold Urey demonstrated that many simple biomolecules could be formed spontaneously from inorganic precursor compounds under laboratory conditions designed to mimic those found on Earth before the evolution of life. Of particular interest was the substantial yield of amino acids obtained, since amino acids are the building blocks for proteins.

In 1957, Sidney Fox demonstrated that dry mixtures of amino acids could be encouraged to polymerize upon exposure to moderate heat. When the resulting polypeptides, or proteinoids, were dissolved in hot water and the solution allowed to cool, they formed small spherical shells about 2 μm in diameter—microspheres. Under appropriate conditions, microspheres will bud new spheres at their surfaces.

Although roughly cellular in appearance, microspheres in and of themselves are not alive. Although they do reproduce asexually by budding, they do not pass on any type of genetic material. However they may have been important in the development of life, providing a membrane-enclosed volume which is similar to that of a cell. Microspheres, like cells, can grow and contain a double membrane which undergoes diffusion of materials and osmosis. Sidney Fox postulated that as these microspeheres became more complex they would carry on more lifelike functions. They would become heterotrophs, organisms with the ability to absorb nutrients from the environment for energy and growth. As the amount of nutrients in the environment decreased, competition for those precious resources increased. Heterotrophs with more complex biochemical reactions would have an advantage in this competition. Over time organisms would evolve that used photosynthesis to produce energy.

One useful discovery made from the research of microspheres is a way to fight cancer on a molecular level. According to Wake Oncologists, "SIR-Spheres micropheres are radioactive polymer spheres that emit beta radiation. Physicians insert a catheter through the groin into the hepatic artery and deliver millions of micropheres directly to the tumor site. The SIR-Spheres microspheres target the liver tumors sparing healthy liver tissue. Approximately 55 physicians in the United States use Sirtex’s SIR-Spheres micropheres in more than 60 medical centers."