Active Transport, Exocytosis and Endocytosis
Active transport requires a direct or indirect input of energy derived from ATP
Moves substances against their concentration gradients; requires cells to expend
Depends on membrane transport proteins
Specific for certain substances
Can be saturated
Two kinds of Active transport
o Primary active transport
The same protein that transports substance also hydrolyses ATP to
power transport directly
o Secondary active transport
Transport indirectly driven by ATP hydrolysis
Transport proteins do not break down ATP
Instead use a favorable concentration gradient of substance,
built up by primary active transport, as their energy source
Primary Active Transport
Moves positively charged ions across membrane
o H+ pumps (proton pumps)
Cells lining stomach
In the plasma membrane pushes hydrogen ions from the cytoplasm to
the cellular exterior
Temporarily bind a phosphate group from ATP during the pumping
o Ca2+ pump
Maintain low intracellular Ca2+ concentration
Pushes Ca2+ from the cytoplasm to the cell exterior and from the
cytosol into the vesicles of the endoplasmic reticulum.
Ca2+ is typically high outside the cells and inside ER vesicles.
A regulatory control of cellular activities as diverse ass secretion,
microtubule assembly, and muscle concentration
o Na+/K+ pump
3 Na+ out, 2 K+ in for every pump cycle
creates negative membrane potential
electrochemical gradient across membrane Secondary Active Transport uses the concentration gradient of an ion established by a
primary pump as their energy source.
Occurs by two mechanisms:
Cotransported solute moves through membrane channel in same
direction as driving ion. A phenomenon known as cotransport.
Sugars such as glucose and amino acids are examples of molecules
actively transported into cells by symport.
Driving ion moves through membrane channel in one direction,
providing energy for active transport