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In terms of membrane transport the gradient is of interest as it contributes to decreased system entropy in the co-transport of substances against their gradient. One of the most important pumps in animal cells is the sodium potassium pump, that operates through the following mechanism: [9]
The transport mechanism depends on the material being moved. Intracellular transport that requires quick movement will use an actin-myosin mechanism while more specialized functions require microtubules for transport. [5] Microtubules function as tracks in the intracellular transport of membrane-bound vesicles and organelles.
In contrast, paracellular transport is the transfer of substances across an epithelium by passing through an intercellular space between the cells. It differs from transcellular transport, where the substances travel through the cell passing through both the apical membrane and basolateral membrane; Renal physiology. Transcellular transport is ...
An example is the sodium-calcium exchanger or antiporter, which allows three sodium ions into the cell to transport one calcium out. [24] This antiporter mechanism is important within the membranes of cardiac muscle cells in order to keep the calcium concentration in the cytoplasm low. [9]
Facilitated diffusion in cell membrane, showing ion channels and carrier proteins. Facilitated diffusion (also known as facilitated transport or passive-mediated transport) is the process of spontaneous passive transport (as opposed to active transport) of molecules or ions across a biological membrane via specific transmembrane integral proteins. [1]
The sodium–potassium pump (a type of P-type ATPase) is found in many cell (plasma) membranes and is an example of primary active transport.Powered by ATP, the pump moves sodium and potassium ions in opposite directions, each against its concentration gradient.
The cell employs a number of transport mechanisms that involve biological membranes: Passive osmosis and diffusion : Some substances (small molecules, ions) such as carbon dioxide (CO 2 ) and oxygen (O 2 ), can move across the plasma membrane by diffusion, which is a passive transport process.
Mechanism of uniport transport across cell membrane. Uniporters work to transport molecules or ions by passive transport across a cell membrane down its concentration gradient. Upon binding and recognition of a specific substrate molecule on one side of the uniporter membrane, a conformational change is triggered in the transporter protein. [27]