ACTIVE TRANSPORT

=Active Transport= In order for a cell to move molecules into / out of the cell against their concentration gradient, the cell must actively pump the molecules across the cell membrane. This is known as active transport and usually involves special proteins found in the cell membrane. [image:http://i.imgur.com/4NxIA0rl.png] [image:http://i.imgur.com/PRgkCPq.gif?2] These proteins are sometimes referred to as '''ion pumps''' because they are often involved in the transport of charged molecules that cannot easily traverse the lipid centre of the membrane. When a particular molecule binds to the protein pump, it changes shape forcing the molecule across the membrane against its concentration gradient. This requires cellular energy in the form of ATP. Some of these protein pumps will transport a single type of molecules, while other can transport two or more molecules in the same or even opposing directions. [image:http://i.imgur.com/1OXzfrj.png?1] '''Key Ideas''': *Active transport is an active process that requires energy (ATP). *Active transport moves molecules against their concentration gradient *Active transport relies on specialised proteins embedded within the membrane