Membrane transport concentration gradient

Active Transporters use the energy of ATP for vectorial transport through a biological membrane against concentration gradient of the transported substrate. 

Biological membranes have complex effects on passive transport by diffusion because they are structured as a mosaic of regions with distinct hydrophobic and hydrophilic properties. Consequently, polarity affects the ability of molecules to pass through biological membranes by passive diffusion. The ability of membrane proteins specifically to admit some polar molecules and exclude others dramatically affects the responses of biological membranes to concentration gradients. 

In the negative feedback mode, the concentration of redox species is the same on both sides of the membrane no concentration gradient exists between the donor and receptor compartments to drive diffusive transport across the pore (11-13). This mode of imaging can be used to obtain topographical maps of the surface where the variation in the SECM tip current arises from differences in the tip-to-sample separation (28). When the tip is far from the sample surface, a steady-state current is measured at the tip,... 

Through these group transfer reactions, ATP provides the energy for anabolic reactions, including the synthesis of informational molecules, and for the transport of molecules and ions across membranes against concentration gradients and electrical potential gradients. 

The function of the Na K ATPase is a complex one. It must (1) pick up one Na in the inside of the cell and transfer it to the extracellular fluid against a concentration gradient, (2) pick up a in the extracellular fluid and then transfer it inside the cell. Obviously this driving of ions through the cell membrane against concentration gradients requires energy and the ion transport must therefore be closely coupled to the hydrolysis of ATP to ADP. 

Active Transport Of Substances Across Cell Membranes. The use of metabolic energy to move substances across membranes against concentration gradients is called active transport. Normally, the substances which can pass... 

Transporter. A transporter is a protein transporting molecules or ions through the cell membrane against a concentration gradient. 

The concentration boundary layer forms because of the convective transport of solutes toward the membrane due to the viscous drag exerted by the flux. A diffusive back-transport is produced by the concentration gradient between the membranes surface and the bulk. At equiUbrium the two transport mechanisms are equal to each other. Solving the equations leads to an expression of the flux ... 

Electrically assisted transdermal dmg deflvery, ie, electrotransport or iontophoresis, involves the three key transport processes of passive diffusion, electromigration, and electro osmosis. In passive diffusion, which plays a relatively small role in the transport of ionic compounds, the permeation rate of a compound is deterrnined by its diffusion coefficient and the concentration gradient. Electromigration is the transport of electrically charged ions in an electrical field, that is, the movement of anions and cations toward the anode and cathode, respectively. Electro osmosis is the volume flow of solvent through an electrically charged membrane or tissue in the presence of an appHed electrical field. As the solvent moves, it carries dissolved solutes. 

Back-diffusion is the transport of co-ions, and an equivalent number of counterions, under the influence of the concentration gradients developed between enriched and depleted compartments during ED. Such back-diffusion counteracts the electrical transport of ions and hence causes a decrease in process efficiency. Back-diffusion depends on the concentration difference across the membrane and the selectivity of the membrane the greater the concentration difference and the lower the selectivity, the greater the back-diffusion. Designers of ED apparatus, therefore, try to minimize concentration differences across membranes and utilize highly selective membranes. Back-diffusion between sodium chloride solutions of zero and one normal is generally [Pg.173]

To achieve the transport of ions against their concentration gradients, the reversible change in the nature of ionophores at the both interfaces of a membrane is necessary, and for this object, many ingenious devices in the structure of ionophores and the transport systems have recently been developed. 

A family of related, membrane-spanning glycoproteins that catalyze the transport of glucose across a lipid bilayer of the plasma membrane along a concentration gradient. 

Glucose transporters are integral membrane proteins that catalyze the permeation of sugars into cells, along or against a concentration gradient. 

As described above, because MAO is bound to mitochondrial outer membranes, MAOIs first increase the concentration of monoamines in the neuronal cytosol, followed by a secondary increase in the vesicle-bound transmitter. The enlarged vesicular pool will increase exocytotic release of transmitter, while an increase in cytoplasmic monoamines will both reduce carrier-mediated removal of transmitter from the synapse (because the favourable concentration gradient is reduced) and could even lead to net export of transmitter by the membrane transporter. That MAOIs increase the concentration of extracellular monoamines has been confirmed using intracranial microdialysis (Ferrer and Artigas 1994). 

In Saccharomyces cerevisiae, as in most eukaryotic cells, the plasma membrane is not freely permeable to nitrogenous compounds such as amino acids. Therefore, the first step in their utilization is their catalyzed transport across the plasma membrane. Most of the transported amino acids are accumulated inside the yeast cells against a concentration gradient. When amino acids are to be used as a general source of nitrogen, this concentration is crucial because most enzymes which catalyze the first step of catabolic pathways have a low affinity for their substrates. 

In bacteria, accumulation of substrates against a concentration gradient can occur through two main classes of transport systems (see [30] for a summary). The prototype of the first class of transporters is the /3-galactoside permease of Escherichia coli (see [31]). It is a relatively simple system involving only a single membrane-bound protein. It catalyzes a lactose-H symport. Other transporters... 

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