Cell and membrane transport
Important molecules, necessary for the functioning of the cell, need to be transported from the external environment to the cell (or from organelles) to the cytoplasm in the cell. The cell does this through the help of proteins that aid the active transport and facilitated diffusion of these molecules into and out of the cell. Types of proteins within the plasma membrane which aid the movement of substances across the cell membrane are transport proteins, receptors and enzymes.
Also see intracellular Ca2+ transport.
The two main types of proteins that take a role in membrane transport are carrier proteins and channel proteins, which span the bilayer and are specific to the solute wishing to be transported.
These two varieties have different ways in which they transport molecules. Carrier proteins, for example, deliver by conformational change. This is where the protein changes shape in order to release the molecule being transported from inside of the membrane to its outside. On the other hand, channel proteins work by creating hydrophilic pores in the membrane. This forms a passageway for mainly ions which operates much more time efficiently[1]. A third way, in which shipment of molecules across the cell membrane occurs, is by use of ATPases that are enzymes assisting in the hydrolysis of adenosine triphosphate into adenosine diphosphate and an inorganic phosphate molecule. This illustrates the importance of proteins needed to perform processes via transport across the cell membrane[2].