facilitated diffusion

facilitated diffusion

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

• differs from simple diffusion as it requires transport protiens

• passive transport

• channel or carrier protein

• crosses cell membrane with help of membrane protein

• needs concentration gradient 

• high to low concentration 

cell membrane

made of double layer of phosopholids

passive transport

requires no energy

facilitated diffusion transport

• passive transport with aid of a membrane protein

• It is utilized by molecules that are unable to freely cross the phospholipid bilayer (e.g., large, polar molecules and ions).

• The process is mediated by two distinct types of transport proteins – channel proteins and carrier proteins.

channel proteins

• Integral lipoproteins which contain a pore which ions may cross from one side of the membrane to the other

• ion-selective and may be gated to regulate the passage of ions 

• move molecules along a concentration gradient

• much faster rate of transport than carrier proteins

carrier proteins 

• Integral glycoproteins which bind a solute and undergo a conformational change to translocate the solute across the membrane.

• only bind a specific molecule via an attachment similar to an enzyme-substrate interaction.

• move molecules against concentration gradients in the presence of ATP

• used in ATP

• much slower rate of transport than channel proteins