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Ch
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: Phospholipids II

⁃ Selectivity of ion channels:
⁃ A sodium ion is smaller than a potassium ion
⁃ hydrated ions have different shell sizes
⁃ when ions are in solution they are hydrated; so there’s a shell around any given
ion in a solution (hydration shell)
⁃ ions must become dehydrated to pass through an ion channel (get rid of
hydration shell)
⁃ carbonyl groups: parts of the amino acids that stick into the selectivity pore
⁃ spacing of potassium & sodium carbonyl groups differ
⁃ carbonyl groups replace (dehydrate) the water around ions (water around ions
are the hydration shell around ions)
⁃ it is probably dehydration energy (ability to strip off the water from these
ions) that’s the primary determinant of ion selectivity in the pore region
of ion channels
⁃ what determines where carbonyl groups go is DNA (protein must fold up in
correct orientation)
⁃ this allows the carbonyl groups to be perfectly spaced
⁃ Water is moved through osmosis:
⁃ there are no water pumps, or water transporters
⁃ all water movement across our cells is an indirect process (our cells have
no direct way of controlling water movement across their membranes)
⁃ there are water channels (aquaporins), but these aren’t passive
⁃ osmosis: water simply follows salt
⁃ animals balance water & electrolytes in tandem to maintain an environment
conducive to cellular function
⁃ so salt is moved & water will follow it via osmosis
⁃ diffusion: the movement of any molecule down its concentration gradient (form
areas of higher concentration to areas of lower concentration- in this case,
across a selectively permeable membrane)
⁃ osmosis: water moves from areas of higher water concentration to areas of
lower water concentration
⁃ water can cross the membrane on its own (just not as effective)
⁃ must cross 2 cell membranes (must go into the cell & outside the other
side of the cell to leave)
⁃ Water Movement Process
⁃ Sodium Potassium pump creates an electrochemical gradient
⁃ creates an electrochemical gradient by having an imbalance of sodium
ions & potassium ions (3 sodium ions moves, & 2 potassium ions move)
⁃ this creates an uneven distribution of charge

Sodium, Chloride, & Potassium will move accordingly, powered largely by the
sodium gradient
⁃ chloride channels allow chloride to move towards the sodium & potassium ions
to balance out the electrochemical gradient
⁃ sodium is moved out of cell & chloride follows it (via chloride channel
protein)
⁃ NaCl is a salt; water wants to follow salts
⁃ other molecules are often co-transported to build up an osmotic gradient as well
⁃ areas of higher salt concentration then become a driving force for osmosis to
fuel the movement of water
⁃ SUMMARY: the movement of water is controlled by the movement of salts (it
will follow glucose or any other salt that has a charge)
⁃ Endocytosis: any process where cells absorb molecules from the surrounding
extracellular env
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parts of the protein to interact w/ diff
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clathrins that come together
⁃ Adapter-Protein Complex (AP): complex of proteins that together can
bind the receptor, the lipid membrane & clathrin
⁃ auxilin: binds to clathirin to recruit HSC70
⁃ HSC70: binds to disassemble the clathrin lattice structure
HSC70 & auxilin work together to change shape of clathrin which allows it to break
down
⁃ Pinocytosis: other form of endocytosis
⁃ Phagocytosis: other form of endocytosis
⁃ once a piece of the membrane has been internalized w/ its cargo it becomes an
intracellular vesicle
⁃









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