5.6 Facilitated Diffusion

• Type of passive transport (no energy!)• High to low concentration

• For molecules that cannot diffuse across the membrane on their own.

• Transport proteins are used

5.6 Facilitated Diffusion

– Transport proteins are specific for the substrate,

– The substrate can be sugars, amino acids, ions, and even water

5.6 Facilitated Diffusion

• Channel Protein: becomes a hydrophilic tunnel for passage

5.6 Facilitated Diffusion– Carrier protein: binds to its passenger, changes

its shape, and releases its passenger on the other side

5.7 TALKING ABOUT SCIENCE: Auquaporins

• Peter Agre researched membrane proteins • Led to discovery of aquaporins

5.7 TALKING ABOUT SCIENCE:

Auquaporins

– Aquaporin: allows for rapid diffusion of water into and out of cells (plant cells, kidney cells, RBCs)

5.8 Active Transport

• Cells have a mechanism for moving a solute against its concentration gradient

– Requires energy (ATP)

– The mechanism alters the shape of the membrane protein through phosphorylation using ATP

Transportprotein

Solute

Solute binding1

Transportprotein

Solute

Solute binding1 Phosphorylation2

Transportprotein

Solute

Solute binding1 Phosphorylation2 Transport3

Proteinchanges shape

Transportprotein

Solute

Solute binding1 Phosphorylation2 Transport3

Proteinchanges shape

Protein reversion4

Phosphatedetaches

5.8 Active Transport

• Cells actively transport Ca2+ out of the cell.• Is calcium more concentrated inside or outside of

the cell?

5.8 Active Transport

5.9 Exocytosis

– used to export bulky molecules, such as proteins or polysaccharides

• material to be transported is packaged within a vesicle that fuses with the membrane

• Example: the excretion of insulin by cells within the pancreas into the bloodstream

5.9 Endocytosis

– used to import substances useful to the livelihood of the cell

• material to be transported is packaged within a vesicle that fuses with the membrane

• There are 3 kinds of endocytosis

Phagocytosis

EXTRACELLULARFLUID

Pseudopodium

CYTOPLASM

Foodvacuole

“Food” orother particle

Foodbeingingested

Phagocytosis:

– engulfment of a solid particle by wrapping cell membrane around it, forming a vacuole

Pinocytosis

Plasmamembrane

Vesicle

Plasma membrane

Pinocytosis

– is the same thing except that fluids are taken into small vesicles

Coatedvesicle

Coatedpit

Specificmolecule

Receptor-mediated endocytosis

Coat proteinReceptor

Coatedpit

Material boundto receptor proteins

Plasma membrane

Receptor-mediated endocytosis

– is where receptors in a receptor-coated pit interact with a specific protein, initiating formation of a vesicle