What are passive carrier proteins? What purpose do they serve?

Which type of passive transport involves the movement of small molecules

Passive carrier proteins are a type of membrane transport proteins.

Transport proteins are integral transmembrane proteins; that is they exist permanently within and span the membrane across which they transport substances.

The proteins may assist in the movement of substances by facilitated diffusion or active transport.

The two main types of proteins involved in such transport are broadly categorized as either channels or carriers.

,A carrier protein is not open simultaneously to the both environment (extracellular and intracellular).

Either its inner gate is open, or outer gate is open.

Carriers have binding sites, but pores and channels do not.

When a channel is opened, thousands to millions of ions can pass through the membrane in one time, but only one or a small amount of molecules can pass through a carrier molecule.

Each carrier protein is designed to recognize only one substance or one group of very similar substances.

Research has correlated defects in specific carrier proteins with specific diseases,Passive carrier proteins are a type or carrier proteins that are used in facilitated diffusion, they are still transmembrane carrier proteins, but these are gated transmembrane channels, meaning they do not internally translocate, nor require ATP to function.

The substrate is taken in one side of the gated carrier, and without using ATP the substrate is released into the cell.

,Facilitated diffusion is the process of spontaneous passive transport (as opposed to active transport) of molecules or ions across a biological membrane via specific transmembrane integral proteins.

Being passive, facilitated transport does not directly require chemical energy from ATP hydrolysis in the transport step itself; rather, molecules and ions move down their concentration gradient reflecting its diffusive nature.

,Examples: GLUT1 (glucose transport), Valinomycin (ion K+ transport).

,Image of facilitated diffusion: