facilitatesdiffuusioon

Facilitatesdiffuusioon, interpreted here as facilitated diffusion, is a passive membrane transport process in which certain substances cross cell membranes with the assistance of specialized membrane proteins, without direct input of cellular energy. It enables polar or charged molecules to move down their concentration gradient, which would be slow or inefficient if they relied on the lipid bilayer alone.

The process is mediated by two main classes of proteins: carrier (or transporter) proteins and channel proteins. Carrier proteins bind the solute on one side of the membrane, undergo a conformational change, and release it on the other side. Channel proteins form hydrophilic pores that allow selective ions or small molecules to diffuse through in response to gradients. Both types increase permeability for specific solutes and are highly selective for their substrates.

Kinetics and regulation are characteristic of facilitated diffusion. The transport is saturable, meaning it has a maximum rate (Vmax) when all transport proteins are occupied. It is substrate-specific and can be inhibited by antagonists or competitive inhibitors that block binding or passage. Some transporters are regulated by cellular signals, such as hormones, which alter the number or activity of available transport proteins.

Examples include glucose transport via GLUT family transporters, amino acid transporters in various tissues, and ion diffusion through specific channels. Water movement through aquaporins is often described as facilitated diffusion, highlighting the role of channels in aiding rapid water flux. Facilitated diffusion contrasts with active transport, which requires energy input to move substances against their gradients.