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Primary Active Transport

The primary active transport that functions with the active transport of sodium and potassium allows secondary active transport to occur . The secondary transport method isstill considered active because it depends on the use of energy as does primary transport.

Source: Boundless. “Primary Active Transport.” Boundless Biology . Boundless !" #ul.!$"%. &etrieved $' Sep. !$"% fromhttps:((www.boundless.com(biology(te)tboo*s(boundless+biology+te)tboo*(structure+and+function+of+plasma+membranes+%(active+transport+,,(primary+active+transport+-- +""/ /(

0ne of the most important pumps in animals cells is the sodium+potassium pump 1 2a 3 +4 3

ATPase 5 which maintains the electrochemical gradient 1and the correct concentrations of 2a 3 and 4 35 in living cells. The sodium+potassium pump moves two 4 3 into the cellwhile moving three 2a 3 out of the cell. The 2a3+43 ATPase e)ists in two formsdepending on its orientation to the interior or e)terior of the cell and its affinity for eithersodium or potassium ions. The process consists of the following si) steps:

• 6ith the en7yme oriented towards the interior of the cell the carrier has a highaffinity for sodium ions. Three sodium ions bind to the protein.

• ATP is hydroly7ed by the protein carrier and a low+energy phosphate groupattaches to it.

• As a result the carrier changes shape and re+orients itself towards the e)terior ofthe membrane. The protein8s affinity for sodium decreases and the three sodiumions leave the carrier.

• The shape change increases the carrier8s affinity for potassium ions and two suchions attach to the protein. Subse9uently the low+energy phosphate group detachesfrom the carrier.

• 6ith the phosphate group removed and potassium ions attached the carrier protein repositions itself towards the interior of the cell.

• The carrier protein in its new configuration has a decreased affinity for potassium and the two ions are released into the cytoplasm. The protein now hasa higher affinity for sodium ions and the process starts again.

Several things have happened as a result of this process. At this point there are moresodium ions outside of the cell than inside and more potassium ions inside than out. orevery three ions of sodium that move out two ions of potassium move in. This results inthe interior being slightly more negative relative to the e)terior. This difference in chargeis important in creating the conditions necessary for the secondary process. The sodium+

potassium pump is therefore an electrogenic pump 1a pump that creates a chargeimbalance5 creating an electrical imbalance across the membrane and contributing to themembrane potential .

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Source: Boundless. “Primary Active Transport.” Boundless Biology . Boundless !" #ul.!$"%. &etrieved $' Sep. !$"% fromhttps:((www.boundless.com(biology(te)tboo*s(boundless+biology+te)tboo*(structure+and+

function+of+plasma+membranes+%(active+transport+,,(primary+active+transport+-- +""/ /(

Source: Boundless. “Primary Active Transport.” Boundless Biology . Boundless !" #ul.!$"%. &etrieved $' Sep. !$"% fromhttps:((www.boundless.com(biology(te)tboo*s(boundless+biology+te)tboo*(structure+and+function+of+plasma+membranes+%(active+transport+,,(primary+active+transport+-- +""/ /(