APBioChap7 Osmosis, Water Potential, etc. Cheat Sheet by fatbuttluver

 Directly uses a source of chemical energy (e.g., ATP) to move molecules across a membrane against their gradient

 Uses an electr­och­emical gradient – generated by active transport – as an energy source to move molecules against their gradient
→Does not directly require a chemical source of energy such as ATP

 Moves Na⁺ out of cells and K⁺ into them
 Electr­ogenic pump
 1. The pump is open to the inside of the cell and binds/­takes up 3 Na⁺ ions
 2. Once the Na⁺ ions bind, the pump is triggered to hydrolize ATP. One P-group is attached to the pump, and then phosph­ory­lated. ADP is released as a by-pro­duct.
 3. Phosph­ory­lation causes the pump to change form so that it then faces the exterior of the cell. Like this, the pump no longer has an affinity for Na⁺ ions, and 3 are released.
 4. Facing this direction, the pump now has an affinity for K⁺ ions. It binds 2 of them which triggers the release of the P-group attached to the pump.
 5. With the P-group gone, the cell once again changes form and then faces towards the interior of the cell.
 6. The pump is now back to step 1, and the cycle repeats.

may be engulfed when no longer needed

defense against infection

 Polar molecules can easily interact with the outer face of the membrane, where the negatively charged head groups are found, but they have difficulty passing through its hydrop­hobic core

 Larger charged and polar molecules, like sugars and amino acids, also need help from proteins

 Osmosis is the movement of water through a semi-p­erm­eable membrane from a region of high concen­tration to a region of low concen­tra­tion, tending to equalise the concen­tra­tions of the water.
 Osmosis is passive transport, meaning it does not require energy to be applied.

 The ability of an extrac­ellular solution to make water move into or out of a cell by osmosis is know as its tonicity.
 A solution's tonicity is related to its osmola­rity, which is the total concen­tration of all solutes in the solution.

 A substance moves from an area of high concen­tration to low concen­tration until its concen­tration becomes equal throughout a space

 Molecules diffuse across the plasma membrane with assistance from membrane proteins, such as channels and carriers
A concen­tration gradient exists for these molecules, so they have the potential to diffuse into (or out of) the cell by moving down it. However, because they are charged or polar, they can't cross the phosph­olipid part of the membrane without help. Facili­tated transport proteins shield these molecules from the hydrop­hobic core of the membrane, providing a route by which they can cross.

 Channel proteins span the membrane and make hydrop­hilic tunnels across it, allowing their target molecules to pass through by diffusion
 Very selective and will accept only one type of molecule for transport
 Aquaporins are channel proteins that allow water to cross the membrane very quickly, and they play important roles in plant cells, red blood cells, and certain parts of the kidney
 Play an important role in electrical transm­ission along membranes (in nerve cells) and in muscle contra­ction (in muscle cells)

 Change their shape to move a target molecule from one side of the membrane to the other
 Will change shape in response to binding of their target molecule, with the shape change moving the molecule to the opposite side of the membrane
Provide hydrop­hilic molecules with a way to move down an existing concen­tration gradient (rather than acting as pumps)