plasma membrane and membrane transport

plasma membrane

* outermost component of cell
* major functions:
* enclose and support cell contents
* determine what moves into and out of the cell

phospholipid bilayer

PM contains two layers of phospholipids (polar heads and nonpolar tails)

polar heads

hydrophilic/water soluble

nonpolar tails

hydrophobic/water insoluble

cholesterol

type of lipid in the PM that helps maintain stability

proteins

* functions include anchoring, recognition, enzymes, receptors, carriers, channels
* include integral proteins and peripheral proteins

integral (intrinsic) proteins

proteins that penetrate the lipid bilayer

peripheral (extrinsic) proteins

proteins that are attached to either the inner or outer surfaces of the lipid bilayer

carbohydrates

* functions include lubrication, anchoring, binding, cell recognition
* include glycocalyx

glycocalyx

carbohydrate portions extend beyond the membrane forming a glycocalyx layer

passive process

* requires no ATP
* examples include diffusion, osmosis, filtration

active process

* requires ATP
* examples include active transport and vesicular transport

solute

any material dissolved in solution

solvent

fluid portion of a solution (usually water)

concentration gradient

* unequal distribution of solutes
* driving force of diffusion where solutes tend to move from high to low concentration

simple diffusion

nonpolar solutes are able to diffuse through nonpolar tails of the PM

channel-mediated facilitated diffusion

solutes are unable to diffuse through nonpolar tails of PM therefore must go through a membrane channel to go down the concentration gradient

carrier-mediated facilitated diffusion

solutes are unable to diffuse through nonpolar tails of PM and are too large to fit through a membrane channel therefore must go through a transport protein to go down the concentration gradient

factors influencing the rate of diffusion

* distance
* temperature
* molecular weight
* molecular size

osmosis

diffusion of water (solvent)

osmotic pressure

* force that determines the direction water moves into a solution
* more solutes in a solution = higher osmotic pressure

isotonic environment

* equal osmotic pressure therefore there is equal water movement into and out of the cell
* RBC is stable and functional

hypertonic environment

* environment has higher osmotic pressure therefore osmosis moves out of the cell


* RBC crenates and is not functional

hypotonic environment

* RBC has higher osmotic pressure therefore osmosis is moving into the cell
* RBC will swell and lyse and is not functional

filtration

process that forces water and solutes through a membrane or capillary wall by hydrostatic pressure

differences between diffusion & osmosis and filtration

* driving force of filtration is pressure
* driving force of diffusion and osmosis is the concentration gradient

similarities between diffusion & osmosis and filtration

both processes are passive (no ATP required)

active transport

uses ATP and carrier molecules to move substances across PM against concentration gradient

vesicular transport

materials move into (endocytosis) or out (exocytosis) of the cell by means of vesicles