Nature of Membrane Carriers The characteristics of carrier-mediated transport processes that we have just described—the high degree of structural specificity and saturation kinetics and competitive inhibition—strongly resemble the characteristics of enzyme-substrate interactions.

The phospholipid bilayer membrane maintains a flux of molecules into the cell, by means of osmosis, passive transport or active transport.

Three common types of passive transport include simple diffusion, osmosis, and facilitated diffusion.

There are two types of active transport: primary active transport that uses adenosine triphosphate (ATP), and secondary active transport that uses an electrochemical gradient.

The cell membrane is imbedded with many membrane transport proteins that allow such molecules to travel in and out of the cell. There are three types of mediated transporters: uniport, symport, and antiport. Things that can be transported are nutrients, ions, glucose, etc, all depending on the needs of the cell.

Carrier-mediated transport combines the process of extraction and stripping in a single unit operation, and it offers the possibility of transporting a component against its own concentration gradient (Ho and Li 1992; Kislik 2010).

Cotransporters are a subcategory of membrane transport proteins (transporters) that couple the favorable movement of one molecule with its concentration gradient and unfavorable movement of another molecule against its concentration gradient.

Plasma membrane is the outermost layer in cells. It separates the content of cell from their external environment. It controls the entry and exit of materials in nd out of cell and hence it is called selectively permeable membrane.