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Transcript of Cell Transport
[high] to [low] "with/down [ ] gradient"
No energy required
Second law of thermodynamics (entropy increases) to reach equilibrium
relatively small, nonpolar molecules (O2, CO2, steroids)
small, polar molecules (H2O)
Requires channel protein
Polar/charged molecules (ions, glucose, amino acids, etc)
Aquaporins: for lots of H2O
Osmosis (diffusion of water)
Passive Transport (simple diffusion)
[solute] or tonicity causes water to move
Na+ is polar; for every 1 Na+ ion, 13 H2O molecules are attracted to it (ionic)
Sweat tastes salty (water follows Na+)
How can we quantify where water is going to move?
[low] to [high] "against [ ] gradient"
Requires energy (ATP)
Needs carrier protein
Na+/K+ Pump: An illustrative example
High [Na+] outside cell, pump 3 Na+ out
Need ATP to change shape of protein (enzyme)
ATP phosphorylates protein at allosteric site, causing conformational change
Low [K+] outside cell, pump 2 K+ in
"cell being picky"
More on this later...
Remember that membranes are selectively permeable!
The original "U-Tube"
Only water can pass through the membrane
Equilibrium results in one side higher but equal concentrations!
Glycoprotein - cell-to-cell recognition
Receptor protein - signal transduction
Ligand (chemical messenger) binds
Factors that Affect Diffusion Rate