| 翻訳と辞書 |
| History of cell membrane theory ： ウィキペディア英語版 |
History of cell membrane theory
Cell theory has its origins in seventeenth century microscopy observations, but it would be nearly two hundred years before a complete cell membrane theory be developed to explain what separates cells from the outside world. By the 19th century it was accepted that some form of semi-permeable barrier must exist around a cell. Studies of the action of anesthetic molecules led to the theory that this barrier might be made of some sort of fat (lipid), but the structure was still unknown. A series of pioneering experiments in 1925 indicated that this barrier membrane consisted of two molecular layers of lipids—a lipid bilayer. New tools over the next few decades would confirm this theory, but controversy remained regarding the role of proteins in the cell membrane. Eventually the fluid mosaic model was composed in which proteins “float” in a fluid lipid bilayer "sea". Although simplistic and incomplete, this model is still widely referenced today.
==Early barrier theories==
Since the invention of the microscope in the seventeenth century it has been known that plant and animal tissue is composed of cells. The plant cell wall was easily visible even with these early microscopes but no similar barrier was visible on animal cells, though it stood to reason that one must exist. By the mid 19th century, this question was being actively investigated and Moritz Traube noted that this outer layer must be semipermeable to allow transport of ions.〔Jacques Loeb, ''The Dynamics of Living Matter''. Columbia University Biological Series, ed. H. F. Osborn and E. B. Wilson. Vol. VIII. 1906. New York: Columbia University Press.〕 Traube had no direct evidence for the composition of this film, though, and incorrectly asserted that it was formed by an interfacial reaction of the cell protoplasm with the extracellular fluid.〔
The lipid nature of the cell membrane was first correctly intuited by Quincke, who noted that a cell generally forms a spherical shape in water and, when broken in half, forms two smaller spheres. The only other known material to exhibit this behavior was oil. He also noted that a thin film of oil behaves as a semipermeable membrane, precisely as predicted.〔J Loeb."The recent development of biology." Science, (1904) 20. 777-785.〕 Based on these observations, Quincke asserted that the cell membrane comprised a fluid layer of fat less than 100 nm thick.〔O Hertwig, M Campbell, and H J Campbell, “The Cell: Outlines of General Anatomy and Physiology.” 1895. New York: Macmillan and Co.〕 This theory was further extended by evidence from the study of anesthetics. Hans Meyer and Ernest Overton independently noticed that the chemicals which act as general anesthetics are also those soluble in both water and oil. They interpreted this as meaning that to pass the cell membrane a molecule must be at least sparingly soluble in oil, their “lipoid theory of narcosis.” Based on this evidence and further experiments, they concluded that the cell membrane might be made of lecithin (phosphatidylcholine) and cholesterol.〔U V Hintzensterna, W Schwarzb, M Goerigc, and H Petermann."Development of the "lipoid theory of narcosis" in German-speaking countries in the 19th century: from Bibra/Harless to Meyer/Overton." The history of anesthesia, (2002) 1242. 609-612.〕 Interestingly, one of the early criticisms of this theory was that it included no mechanism for energy-dependent selective transport.〔B Moore, Secretion and glandular mechanisms, in Recent advances in physiology and biochemistry, L. Hill, Editor. 1908. Edward Arnold: London.〕 This “flaw” would remain unanswered for nearly half a century until the discovery that specialized molecules called integral membrane proteins can act as ion transportation pumps.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
■ウィキペディアで「History of cell membrane theory」の詳細全文を読む
スポンサード リンク
| 翻訳と辞書 : 翻訳のためのインターネットリソース |
Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.
|
|