Notes

Membrane Proteins
Channel - allow specific molecules to cross membrane
Carrier - bind molecules first, then move them across
Cell recognition - glycoproteins that recognize "self" (This is me -> that is you {immune system})
Receptor - binds signal molecules that elicit a response (Hormones - Pain meds)
Enzymatic - directly carry out metabolic reactions ( metabolism, something goes in - something else comes out)
Junction - hold cells together, aid in cell signaling

Molecular Movement across membranes
Two types of molecular movement that are important to life (Passive and active)
PASSIVE transport - no cell energy is used
ACTIVE transport - cell energy (ATP) is used
Passive transport moves water, ions, and other small substances
Active transport moves organic molecules and other large substances - also very important for producing concentration gradients
Concentration gradient is a difference in concentration in one part of a solution vs another part (or) one side of the membrane vs the other side
When concentration gradient is present diffusion is likely to occur and energy is lost
High concentration = high energy / low concentration = low energy
When water moves from high concentration to low concentration energy can be used by the cell
Passive transport -> going down hill and no energy is required
Active transport -> going uphill and energy is required

PASSIVE TRANSPORT
Diffusion - the movement of molecules from areas of high concentration to areas of low concentration (going down hill - losing energy)
*Molecules diffuse down their concentration gradients
*A concentration gradient exists when a molecule is in a higher concentration in a part of the solution
*A membrane must be permeable to the molecule in question for diffusion to occur across it
*Equilibrium is achieved when gradient is lost - ALL solution states are equal
**Diffusion stops but molecules continue moving around
Facilitated diffusion - diffusion of molecules that normally cannot diffuse through membranes
*Uses transport proteins to helps molecules diffuse
*Molecules move down their concentration gradient
*No cellular energy is used to move the molecules
*Facilitated diffusion is how water, ions, glucose, and amino acids get into cells
Osmosis - diffusion of water through a membrane
* Membrane is permeable to water but not to solute
* Water will move from the side with the higher concentration to that of lower concentration
* Relative to cell contents, there are 3 types of solutions
*1. Isotonic - Solute concentrations are equal on either side of the membrane
** Water moves in and out equally; no gain or loss in less (Re-hydrates you)
*2. Hypertonic - Solute concentration is higher in the solution than in the cell (Super salty)
**The cell loses water to solution and shrinks (Salting fish)
*3. Hypotonic - Solute concentration is lower in the solution than the cell - Swells and bursts

ACTIVE TRANSPORT
Uses cell energy in the form of ATP molecules (Adenosine triphosphate)
Molecules are moved across the membrane from lower to higher concentration (Up the gradient)
*Increases the concentration gradient
*This induces diffusion, when and where it's possible
* Pumps are systems of active transport that utilize membrane proteins

The Sodium- Potassium pump
Found in plasma membrane of all cells in all animals
Maintains cell resting potential ( Slight electric charge)
Produces the electric current in nerve and muscle tissue
Membrane protein uses ATP to move 3 Na+ ions out of the cell while it moves 2 K+ ions into the cell