Sunday, March 6, 2011

Methods of Transport: Active

Active transport in cells requires the use of energy to transport products against the concentration gradient. 30-40% of all energy within a cell is used for transport.

Individual molecules:
Transport proteins actively pump molecules in/out of the cell using energy.
An example of such a pump would include the sodium-potassium pump. Three sodium ions within the cytosol bind to the protein causing it to change shape. The protein can then attain a phosphate group from ATP causing another change in shape that releases the sodium ions outside the cell, and allowed potassium ions to bond to the protein. The phosphate group then dislocates making the protein return to its original shape releasing the potassium ions within the cell.

Cells like to have a high concentration of potassium ions within them, and a low sodium ion concentration. To allow this to work,

In Bulk:
In bulk, material is moved into/out of a cell using endocytosis and exocytosis.

Involves the movement of material into the cell through the creation of new vesicles from the cell membrane.
When liquids are brought in, it is called, pinocytosis.
When solids are brought in, it is called, phagocytosis.

Involves the movement of material out of the cell through fusing vesicles with the plasma membrane.

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