Cells: Facilitated vs Active Transport

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Cells Facilitated vs Active Transport
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Diffusion and osmosis are fine for moving some
things into and out of the cell when

• small molecules like O2, CO2 and H2O are moving
• the direction of movement is with the
  concentration gradient.

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Carrier proteins are needed to move other solutes.
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Carrier proteins embedded in the bilayer function
as tunnels

• called transport proteins or carrier proteins
• each evolved to transport certain molecules
• can handle things larger than water
• can handle ions like Na and K

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open carrier protein
closed carrier protein
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Facilitated diffusion uses carrier proteins as
tunnels for larger molecules and ions.

• molecules flow in or out down their concentration
  gradients
• no energy is required

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• Facilitated helped by protein
• Diffusion movement down concentration gradient

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In this diagram, potassium ions flow out of the
cell through a carrier protein down their
concentration gradient.
Therefore, the diffusion of potassium is being
facilitated by the carrier protein.
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Active transport is more like a pumping action.

• carrier proteins move molecules up their
  concentration gradient
• Against natural direction of diffusion
• Allows cells to concentrate molecules and ions.
• requires energy - it costs the cell!!!!

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In this diagram, three different solutes are
moved against the gradient into the cell.
glucose
Na ion
amino acid
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Facilitated diffusion and active transport both
use carrier proteins embedded in the phospholipid
bilayer.
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Differences