Breaching the Barrier

Transporter proteins are integral membrane proteins that selectively mediate the passage of molecules across the otherwise impermeable barrier imposed by the phospholipid bilayer that surrounds all cells and organelles. The identification of more than 360 families of transporters biochemical and genomic analyses highlights the importance of transport processes to cells. Among the most fascinating transporters are those that act as molecular , translocating their substrates across membranes against a concentration gradient; this thermodynamically process is powered by coupling to a second, energetically favorable process such as ATP hydrolysis or the movement of a second solute down a transmembrane gradient.