cell membrane Flashcards
characteristics of cell membrane
- boundary between inside/outside of cell
- liquid
- only 8nm thick
selectively permeable
can “choose” what goes into or out of cell, direct consequence of its structure
fluid mosaic model
fluid: proteins and phospholipids can move laterally (switches positions about 10^7 times/sec), kinked tails enhance fluidity
definition of a model
hypothesis that is updated as new information is discovered
cholesterol
keeps membrane from solidifying (see pic i’m notes). a “fluidity buffer that resists change in membrane fluidity that can be caused by changes in temperature
carbohydrates
- used for cell recognition (MHC class 1)
- most = glycoproteins (covalently bonded to proteins)
- some = glycolipids
- examples: A B O blood antigens
permeability of bilayer nonpolar molecules
like CO2, N2, O2, hydrophobic and can therefore dissolve in the lipid bilayer (no proteins needed)
permeability of bilayer polar molecules
such as water, ions, glucose; hydrophilic and must use a membrane protein
membrane proteins
- doesn’t matter if it’s hydrophilic or hydrophobic
- peripheral (in or out not both) or integral (within the membrane)
- used to move materials, communicate, attachment, as enzymes, etc
ion channels
specific to each ion, may be gated, diffusion, active transport
aquaporin
moves water, osmosis, passive transport
carrier proteins
- moves glucose in facilitated diffusion, passive transport
- with ATP can be a pump (Na/K pump), active transport
Na/K pump
- carrier protein, moves sodium out of the cell and potassium into the cell
- 3Na+ and 2K- per cycle
- 150 cycles a second, lots of ATP
cell charge
because of unequal numbers being pumped in the Na/K pump, the cell takes on a negative charge. also known as a protein gradient
active transport
uses cell energy (ATP) to move materials in/out of cell. ALWAYS goes from low to high concentrations (against the concentration gradient)
