Cell Transport Notes
Learning Targets
8. Explain the significance of the selectively permeable membrane to the transport of molecules.
9. Compare and contrast passive and active transport.
10 Explain the terms: hypotonic, hypertonic or isotonic in relationship to the internal environments of cells.
Passive & Active
Kinds of Membrane Proteins
Channel Proteins
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Membrane proteins
–
Opening through the
–
Always
–
Anything that fits, gets through
–
“Facilitated” Diffusion
•
Ex.
Carrier Proteins
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Proteins bind to a substance 
•
Highly specific
•
Movement is VERY slow
•
Ex. Glucose carriers
Receptor Proteins
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Bind to a specific molecule (ligand)
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Transmit signal to
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Start “reaction” inside molecule
•
Ex. hormones
Enzymatic Proteins
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Enzymes that are Carry out reactions
•
Ex. ATP Synthase  generate ATP
Cell Recognition Proteins
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Carbohydrate “chains” attached to membrane proteins (Glycocalyx  “sugar” coat)
•
Functions:
Selective Permeability
•
Some substances can get through, some
–
Glucose & other ions, molecules have to use
Passive Transport
Diffusion
•
Dumb, stupid, blind molecules! They don’t see, think or feel!
•
Molecules are driven by
•
Molecules move from
•
Solutes may be:
to
•
•
concentration 
(solid, liquid or gas)
Ions (cations [+], anions [-])
•
Solvent (biological) is water
•
How O2 & CO2 pass in & out of cell membrane
Osmosis
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Diffusion of solvent molecules (usually water)
•
Tonicity:
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Ability of surrounding solutions to cause cells to gain/lose water
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Isotonic
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Hypertonic
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Hypotonic
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Osmoregulation-control of water balance
Results
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Plasmolysis  cell shrinks
•
Cytolysis  cell bursts
Facilitated Diffusion
•
•
Doesn’t require
•
Some hydrophilic
–
•
Others change shape when molecule binds to it
–
•
Other hydrophilic molecules can
Allows protein to dump molecule out on
Aquaporins
–
Protein channel just for
–
Leads to
•
Plant cells, RBC, kidney cells
Active Transport
•
Moves substance
•
“Carrier-mediated”—
•
Always requires addition of
Na+/K+ pump
•
With the help of
•
Na+ leave cell
•
K+ enter cell
“Bulk” Transport:
Endocytosis
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Phagocytosis: Ingestion of
•
Pinocytosis: Ingestion of
Exocytosis
•
•
•
•
Vesicles fuse with
Eliminate
Secretion of molecules
Contractile vacuoles