Facilitated diffusion

Facilitated Diffusion

Facilitated diffusion (pronunciation: fuh-SIL-i-tay-ted di-FYOO-zhuhn) is a type of passive transport that allows substances to cross cell membranes with the aid of transport proteins.

Etymology

The term "facilitated diffusion" is derived from the Latin words "facilis" meaning "easy" and "diffundere" meaning "to spread out". It refers to the process that makes the diffusion of certain molecules across a cell membrane easier.

Process

In facilitated diffusion, molecules move down their concentration gradient, from an area of high concentration to an area of low concentration. This process does not require energy (ATP), hence it is a type of passive transport. The molecules that are transported via facilitated diffusion are either not soluble in lipids or are too large to pass through the pores in the cell membrane. These molecules are transported across the cell membrane with the help of transport proteins.

Types of Transport Proteins

There are two types of transport proteins involved in facilitated diffusion: channel proteins and carrier proteins. Channel proteins form a water-filled channel that allows specific molecules to pass through. Carrier proteins, on the other hand, bind to the molecule and change shape to shuttle the molecule across the membrane.

Related Terms

• Active transport: A type of cellular transport that requires energy to move substances against their concentration gradient.
• Osmosis: The diffusion of water across a selectively permeable membrane.
• Ion channel: A type of protein that allows ions to pass through the cell membrane.

See Also

• Cell membrane
• Passive transport
• Concentration gradient
• ATP
• Channel protein
• Carrier protein

External links

• Medical encyclopedia article on Facilitated diffusion
• Wikipedia's article - Facilitated diffusion

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