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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Elasticity of cell membranes ： ウィキペディア英語版 Elasticity of cell membranes A cell membrane defines a boundary between the living cell and its environment. The primary constituent of a membrane is a phospholipid bilayer that forms in a water-based environment due to the hydrophilic nature of the lipid head and the hydrophobic nature of the two tails. In addition there may be other lipids and proteins in the membrane, the latter typically in the form of isolated rafts. Of the numerous models that have been developed to describe the deformation of cell membranes, a widely accepted model is the fluid mosaic model proposed by Singer and Nicolson in 1972. In this model, the cell membrane surface is modeled as a two-dimensional fluid-like lipid bilayer where the lipid molecules can move freely. The proteins are partially or fully embedded in the lipid bilayer. Fully embedded proteins are called integral membrane proteins because they traverse the entire thickness of the lipid bilayer. These communicate information and matter between the interior and the exterior of the cell. Proteins that are only partially embedded in the bilayer are called peripheral membrane proteins. The membrane skeleton is a network of proteins below the bilayer that links with the proteins in the lipid membrane. ==Elasticity of closed lipid vesicles== The simplest component of a membrane is the lipid bilayer which has a thickness that is much smaller than the length scale of the cell. Therefore the lipid bilayer can be represented by a two-dimensional mathematical surface. In 1973, based on similarities between lipid bilayers and nematic liquid crystals, Helfrich proposed the following expression for the curvature energy per unit area of the closed lipid bilayer where $k\_c,\backslash bar$ are bending rigidities, $c\_0$ is the spontaneous curvature of the membrane, and $H$ and $K$ are the mean and Gaussian curvature of the membrane surface, respectively. The free energy of a closed bilayer under the osmotic pressure $\backslash Delta\; p$ (the outer pressure minus the inner one) as: where ''dA'' and ''dV'' are the area element of the membrane and the volume element enclosed by the closed bilayer, respectively, and ''λ'' is the surface tension of the bilayer. By taking the first order variation of above free energy, Ou-Yang and Helfrich derived an equation to describe the equilibrium shape of the bilayer as: They also obtained that the threshold pressure for the instability of a spherical bilayer was where $R$ being the radius of the spherical bilayer. Using the shape equation (3) of closed vesicles, Ou-Yang predicted that there was a lipid torus with the ratio of two generated radii being exactly $\backslash sqrt$. His prediction was soon confirmed by the experiment Additionally, researchers obtained an analytical solution to (3) which explained the classical problem, the biconcave discoidal shape of normal red cells. 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「Elasticity of cell membranes」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.