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Plasma membrane, permeability structure

There are aspects of cell membranes other than their permeability to water and solutes that also play a critical role in the responses of cells to freezing. The structure of the plasma membrane allows cells to supercool and probably determines their ice-nucleation temperature. The nucleation temperature along with the permeability of membranes to water are the chief determinants of whether cells cooled at... [Pg.379]

Membranes are highly viscous, plastic structures. Plasma membranes form closed compartments around cellular protoplasm to separate one cell from another and thus permit cellular individuality. The plasma membrane has selective permeabilities and acts as a barrier, thereby maintaining differences in composition between the inside and outside of the cell. The selective permeabilities are provided mainly by channels and pumps for ions and substrates. The plasma membrane also exchanges material with the extracellular environment by exocytosis and endocytosis, and there are special areas of membrane strucmre—the gap junctions— through which adjacent cells exchange material. In addition, the plasma membrane plays key roles in cellcell interactions and in transmembrane signaling. [Pg.415]

The inhibition of amino-acid transport has been regarded as the main toxic effect of mercury compounds [82], The biochemical mechanism underlying the inhibition is unclear. In unfertilized sea-urchin eggs an interaction with the amino-acid carrier was found, whereas in fertilized eggs inhibition of amino-acid transport was indirect and might result from an elevation of the Na + content of the egg caused by the inhibition of the Na+ pump [83]. The action on the diffusional process could be mediated by an effect on membrane phospholipids or on membrane proteins, or by interaction with Ca2+ which stabilizes membrane structure. Mercuric chloride in skate liver cells inhibited amino acid transport, decreased Na + /K + -ATPase (adenosinetriphosphatase) activity, impaired volume regulatory mechanisms and increased the permeability of the plasma membrane to potassium [84]. It has been suggested that... [Pg.195]

A cell is enclosed by a lipid bilayer known as the plasma membrane. In Vignette 1.2 in Chapter 1 we discussed an example of a membrane, a complex structure with a mosaic of embedded or adsorbed moieties such as proteins. It is these membranes that protect the intracellular contents from the exterior environment of the cells and regulate the transport of materials into and out of the cells. They can also act as signal transducers and control the electrical excitation in the nervous system by altering the (membrane) permeability to particular ions in response to stimuli. Such electrical activities can propagate over long distances and represent one of the most spectacular of the membrane functions. [Pg.106]

Phospholipids, components of every cell membrane, are active determinants of membrane permeability. They are sources of energy, components of certain enzyme systems, and involved in lipid transport in plasma. Because of their polar nature, phospholipids can act as emulsifying agents. The structure of most phospholipids resembles that of triglycerides except that one fatty acid radical has been replaced by a radical derived limn phosphoric acid and a nitrogen base. c.g.. choline or serine. [Pg.1002]

Antibacterial antibiotics normally act by either making the plasma membrane of bacteria more permeable to essential ions and other small molecules by iono-phoric action or by inhibiting cell wall synthesis (see section 7.2.2). Those compounds that act on the plasma membrane also have the ability to penetrate the cell wall structure (Appendix 3). In both cases, the net result is a loss in the integrity of the bacterial cell envelope, which leads to irreversible cell damage and death. [Pg.135]

Normal cellular physiology depends on the ability of ions to move across cell membranes. Ion channels are highly specialized transport proteins that facilitate this movement by forming regulated ion-permeable routes through the membranes of nearly all excitable and non-excitable cells. They are found in plasma membranes and in the membranes of intracellular organelles. Plasma membrane ion channels display significant structural and functional diversity (Ashcroft 2006) and... [Pg.69]

The cornified cell envelope is the outermost layer of a corneocyte, and mainly consists of tightly bundled keratin filaments aligned parallel to the main face of the corneocyte. The envelope consists of both protein and lipid components in that the lipid is attached covalently to the protein envelope. The envelope lies adjacent to the interior surface of the plasma membrane. " The corneocyte protein envelope appears to play an important role in the structural assembly of the intercellular lipid lamellae of the stratum corneum. The corneocyte possesses a chemically bound lipid envelope comprised of A-co-hydroxyceramides, which are ester linked to the numerous glutamate side chains provided possibly by both the ot-helical conformation and p-sheet conformation of involucrin in the envelope protein matrix. In the absence of A-oo-hydro-xyceramides, the stratum corneum intercellular lipid lamellae were abnormal and permeability barrier function was disrupted. [Pg.1311]


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Membranes plasma

Membranes structure

Membranes structured

Membranes, permeable

Plasma membrane structure

Plasma structuring

Structure-permeability

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