Example Cell Membrane

FIGURE 75. Self-assembly of the Tobacco Mosaic Virus (Y tambe, 2005, Wikimedia Commons). 

In the tobacco mosaic virus, the capsomers first form a ring. Each ring interacts with a special pattern of RNA units. The special sequence is called a pac site and acts as a stopper so that the rings do not slide off as additional rings are added. The additional capsomer disks thread onto the helical arrangement to form a complete capsid, and growth continues until no more disks can thread onto the structure. 

The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane allows for the selective transport of materials such as ions and proteins into the cell. It both protects the cell from outside forces and maintains the optimum balance of nutrients inside the cell. 

FIGURE 7.7. (a) Phosphatldylethanotamine, (b) phosphatidylserine, (c) phosphatidylino-sitol and (d) phosphatidytgtycerol. 

The cell membrane is made of a lipid bilayer with embedded proteins. Cell membranes are involved in many eellular proeesses such as cell adhesion, ion eonductivity and eell signaling. The eell membrane consists of three elasses of lipids phospholipids, glyeolipids, and cho-lesterols. The amount of each depends upon the t) e of eell, but phospholipids are the most abimdant. The membrane is held together via non-covalent interaetions of the hydrophobic tails, but the structure is quite fluid and not fixed in place. Under physiological conditions, phos- 

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Spin-labelling of free, or cell-surface, sialic acids has been used in order to obtain information about the rate of rotational orientation of the label after attachment to macromolecules this knowledge is important in the investigation of the orientation and mobility of sialogly-coproteins in, for example, cell membranes. In a first approach, the label was introduced into the carboxyl groups by a carbodiimicle-me-diated, amidation procedure.177 This method is, however, not specific... 

However, as illustrated in Figure 10.2, living tissue has capacitive properties because of, for example, cell membranes. Therefore, the u and i signals are not in-phase, and impedance and admittance are complex quantities. They are written in bold characters and can be decomposed in their in-phase and quadrature components... 

Polyethers. Antibiotics within this family contain a number of cycHc ether and ketal units and have a carboxyHc acid group. They form complexes with mono- and divalent cations that ate soluble ia aoapolar organic solvents. They iateract with bacterial cell membranes and allow cations to pass through the membranes causiag cell death. Because of this property they have been classified as ionophores. Monensia, lasalocid, and maduramicia are examples of polyethers that are used commercially as anticoccidial agents ia poultry and as growth promotants ia mmiaants. 

A chemical must have certain physicochemical properties to elicit an endocrine disrupting effect. For example, the ability to enter the body and to cross the cell membrane into the cellular medium requires a degree of lipophilicity. Fipophilic potentials may be compared by reference to the chemical s octanol-water coefficient (usually expressed as log K ). This property, together with molecular size and chemical structure, has an important influence on the bioacciimiilation... 

Maintenance of electrical potential between the cell membrane exterior and interior is a necessity for the proper functioning of excitable neuronal and muscle cells. Chemical compounds can disturb ion fluxes that are essential for the maintenance of the membrane potentials. Fluxes of ions into the cells or out of the cells can be blocked by ion channel blockers (for example, some marine tox-... 

Dasgupta and Jacobs [29] patented a concept of using a gel layer in combination with a microporous membrane. The gel layer acts as an adhesive bridge between separator and electrodes, just as in the flat pack Zn/MnC cell [30], The microporous membrane (for example, Celgard membrane) provides excellent mechanical... 

An oligomeric protein that spans a cell membrane forming a regulated pore through which Ca2+ can pass. Ca2+ channels differ considerably in their selectivity for Ca2+ over other cations For example DP3R are poorly selective, voltage-dependent Ca2+ channels are vety selective. 

Some drains act on the body by changing the cellular environment, either physically or chemically. Physical changes in the cellular environment include changes in osmotic pressures, lubrication, absorption, or the conditions on the surface of the cell membrane An example of a drag that changes osmotic pressure is mannitol, which produces a change in the osmotic pressure in brain cells, causing a reduction in cerebral edema A... 

A solid emulsion is a suspension of a liquid or solid phase in a solid. For example, opals are solid emulsions formed when partly hydrated silica fills the interstices between close-packed microspheres of silica aggregates. Gelatin desserts are a type of solid emulsion called a gel, which is soft but holds its shape. Photographic emulsions are gels that also contain solid colloidal particles of light-sensitive materials such as silver bromide. Many liquid crystalline arrays can be considered colloids. Cell membranes form a two-dimensional colloidal structure (Fig. 8.44). 

Depolarization of the cell membrane, for example, favors such events. It should also be noted that any mechanism which affects the action of the Na K pump and the Na transmembrane gradient will also affect the Na Ca exchanger flux. 

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