Membrane, biological cell consistency

Natural biological membranes consist of lipid bilayers, which typically comprise a complex mixture of phospholipids and sterol, along with embedded or surface associated proteins. The sterol cholesterol is an important component of animal cell membranes, which may consist of up to 50 mol% cholesterol. As cholesterol can significantly modify the bilayer physical properties, such as acyl-chain orientational order, model membranes containing cholesterol have been studied extensively. Spectroscopic and diffraction experiments reveal that cholesterol in a lipid-crystalline bilayer increases the orientational order of the lipid acyl-chains without substantially restricting the mobility of the lipid molecules. Cholesterol thickens a liquid-crystalline bilayer and increases the packing density of lipid acyl-chains in the plane of the bilayer in a way that has been referred to as a condensing effect. 

The lyotropic liquid crystalline phases relevant to biological systems consist of water and lipids and usually proteins also. The lipids listed in Table I occur in cell membranes all form liquid crystalline phases with water. 

Biological cell membranes are multi-component systems consisting of a fluid bilayer lipid membrane (BLM) and integrated membrane proteins. The main structural features of the BLMs are determined by a wide variety of amphiphilic lipids whose polar head groups are exposed to water while hydrocarbon tails form the nonpolar interior. The BLMs act as the medium for biochemical vectorial membrane processes such as photosynthesis, respiration and active ion transport. However, they do not participate in the corresponding chemical reactions which occur in membrane-dissolved proteins and often need redox-active cofactors. BLMs were therefore mostly investigated by physical chemists who studied their thermodynamics and kinetic behaviour . ... 

Membranes play an important role in natural science and for many technical applications. Depending on their purpose, their shape can be very different. For instance, membranes include porous or non-porous films, either supported or non-supported, with two interfaces surrounded by a gas or by a liquid. Important properties of non-porous membranes are their permeability for certain compounds and their stability. In biological cells their main task is to stabilize the cell and to separate the cell plasma from the environment. Furthermore, different cells and cell compartments have to communicate with each other which requires selective permeability of the membranes. For industrial applications membranes are often used for separation of gases, liquids, or ions. Foams and emulsions for instance are macroscopic composite systems consisting of many membranes. They contain the continuous liquid phase surrounded by the dispersed gas phase (foams) or by another liquid (emulsions). Beside these application possibilities membranes give the opportunity to investigate many questions related to basic research, e.g. finite size effects. 

The mechanism of action of insulin is complex and can be divided into three parts. The first part is the binding of insulin to its receptor on the cell membrane the second consists of postreceptor events and the third consists of biological responses. 

Biological membranes that encapsulate and give strength to cells consist primarily of bilayers of phospholipids. In the bilayer... 

One of the typical examples of such biomolecular interfaces is a membrane , a two-dimensional molecular array which forms the boundary of biological cells. These membranes are composed of lipids and proteins. Of these, the lipid molecules which are amphipathic (a molecule consisting of two parts, each of which has an affinity for a different phase), are considered to be responsible for maintaining the two-dimensional molecular structure the protein molecules, which perform a variety of biochemical functions, are often associated with (in/on) these lipid bilayer membranes (Figure 16). 

A prime motivation to investigate membranes arises from biology in our 3D world [8]. The lipid bUayer is the most elementary and indispensable structural component of biological membranes, which form the boundary of aU cells and cell organelles [9]. In biological membranes, the bilayer consists of many different lipids and other amphiphiles. Biomembranes are decorated ... 

During recent years much information has been obtained about the structure of biological membranes. This information has come in part from biochemical studies (the isolation of different chemical compounds from the cell membranes), x-ray diffraction, electron-spin and nuclear-spin magnetic resonance, spectroscopy, and especially the use of the electron microscope. Cell membranes, such as the membrane of the red blood cell, consist of about equal amounts of lipids and proteins. There is... 

All biological life (disregarding viruses that only show some properties of life) is composed of cells or collections of cells. At the most basic functional level, a cell consists of a collection of internal structures that are immersed in intracellular fluid and separated from the outside by a cell membrane, which is also called plasma membrane or plasmalemma. There are other membranes of great importance in biology, e.g., those surrounding the nucleus of an eukaryote cell, but this entry is focused on the electrochemistry of the... 

A lyotropic L.C. consists of two or more components that exhibit L.C. properties in certain concentration ranges. In the lyotropic phases, solvent molecules fill the space around the compounds to provide fluidity to the system. In contrast to thermotropic L.C.s, these lyotropics have another degree of freedom, i.e., the concentration, which enables them to induce a variety of different phases. Since lyotropic L.C.s rely on a subtle balance of intermolecular interactions, it is often more difficult to analyse their structures and properties than those of thermotropic L.C.s. Lyotropic L.C. nanostructures are abundant in living systems. Accordingly, lyotropic L.C.s attract particular attention in the field of biomimetic chemistry. In particular, biological membranes and cell membranes are a form of L.C. Their constituent rod-like molecules e.g., phospholipids) are organized perpendicularly to the membrane surface, yet the membrane is fluid and elastic. The constituent molecules can flow in-plane quite easily, but tend not to leave the membrane, and can flip from one side of the membrane to the other with some difficulty. These... 

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