Everything about Active Transport totally explained
Active transport (sometimes called
active intake because of the absorbing movement of particles) is an energy-requiring process that moves material across a cell membrane and up the concentration gradient. The cell uses active transport in three situations: when a particle is going from low to high concentration, when particles need help entering the membrane because they're selectively impermeable, and when very large particles enter and exit the cell.
Classes of pumps
ABC pumps
ABC class pumps transport small molecules across membranes. They are also called the ABC superfamily. They consist of two transmembrane domains, and two ATP binding domains. ABC pumps are involved in the transport of small molecules,
phospholipids and
lipophilic drugs in
mammalian
cells. In
bacteria they transport
amino acids, sugars and
peptides.
P-Class pumps
P-class pumps use ATP to transport
ions against a gradient. They are
phosphorylated during transport, which is different from the other classes of active transport pumps.
Some examples of P-class pumps are the
sodium-potassium pump,
calcium transport in
muscle cells and the
hydrogen-potassium pump in the
apical membrane of the
stomach.
V-Class proton pumps
V-class proton pumps are a type of
ATPase. They use the energy released by the
hydrolysis of
ATP to move
protons against their concentration gradient. All proteins that fall into this class have two structural
domains. One domain called the V
0 domain is made of 5 subunits and is involved in
translocation of the protein. The other domain is called the V
1 domain which is composed of 8 subunits and is involved in
ATP-hydrolysis.
V-class proton pumps are found in a wide variety of
organelle membranes. In
fungi,
yeast and
plant cells they're found in
Vacuole membranes. In animals they're found in the membranes of
lysosomes and
endosomes. V-class proton pumps are also found in the plasma membranes of
macrophages
,
osteoclasts
, and
renal intercalated cells.
The function of this class of pump is strictly to transport
protons across the membrane that they're embedded within. Transporting protons across a membrane can decrease the
pH on one side of the membrane which can be critical for organelle functioning.
Decreasing the pH of endosomes is also important for the entry of some membrane bound
viruses. The viral protein
haemagglutinin is located on the surface of the
Influenza virus and the acidification provided by this protein aids in viral entry.
V-class pumps located in cell membranes which also have critical functions to the cell. In renal intercalated cells these pumps secrete protons into the fluid in the kidneys, helping to maintain an optimal pH in the kidneys.
In
humans,
mutations in the genes coding for this protein can lead to
metabolic acidosis;
a potentially deadly
disease.
F-Class proton pumps
Uses H
+ gradient in order to produce ATP. Can also work in the reverse direction.
Role in neurons
Further Information
Get more info on 'Active Transport'.
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