SUBMITTED TO:

Dr. FEROZA WATTOO

SUBMITTED BY:

WAQAS NAWAZ 11-arid-975

ZAHID NAZIR 11-arid-976

ZEESHAN AHMED 11-arid-978

Facilitated diffusion

BIOCHEMISTRY-101

Facilitated diffusion Large polar molecules such as

glucose and amino acids, cannot diffuse across the phospholipid bilayer. Also ions such as Na+ or Cl- cannot pass.

These molecules pass through protein channels instead. Diffusion through these channels is called FACILITATED DIFFUSION.

Movement of molecules is still PASSIVE just like ordinary diffusion, the only difference is, the molecules go through a protein channel instead of passing between the phospholipids.

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Gas exchange at the alveoli — oxygen from air to

blood, carbon dioxide from blood to air. Gas exchange for photosynthesis — carbon dioxide

from air to leaf, oxygen from leaf to air. Gas exchange for respiration — oxygen from blood to

tissue cells, carbon dioxide in opposite direction. Transfer of transmitter substance — acetylcholine

from presynaptic to postsynaptic membrane at a synapse.

Osmosis — diffusion of water through a semipermeable membrane.

Major Examples Of Diffusion

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Facilitated Diffusion through a membrane

Cell membrane

Inside cell Outside cell

Protein channel

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Facilitated Diffusion through a membrane

Cell membrane

Inside cell Outside cell

Protein channel

diffusion

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Facilitated Diffusion through a membrane

Cell membrane

Inside cell Outside cell

Protein channel

diffusion

EQUILIBRIUM

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Facilitated Diffusion:Molecules will randomly move through the opening like pore, by diffusion. This requires no energy, it is a PASSIVE process. Molecules move from an area of high concentration to an area of low conc.

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Facilitated Diffusion

Two major groups of integral membrane proteins are involved in facilitated diffusion;

Carrier proteins

Ion Channels 

Ion channels allow currents to be carried across the membrane and are thus of particular importance in the physiology of excitable cells like neurons

Bind a specific type of solute Discharges the solute

Certain of the hexose transporters, which transport glucose and similar monosaccharides into and out of cells

Carrier protein

Not really bind the solute Faster than by carrier proteins Contain a "gate" which is functions to

control the channel's permiability

Ion Channels

Facilitated Diffusion of Glucose