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)
passive transport
- materials move across a cell membrane with/down the concentration gradient with no energy supplied by the cell (kinetic energy).
- diffusion, osmosis, facilitated diffusion
diffusion
movement of molecules from high to low concentration without energy from cell until equilibrium is reached
conditions that make diffusion faster
higher temperature, larger surface area, higher concentration gradient, smaller particles, medium (solid=slow, liquid=fast, gas=fastest)
osmosis
moving water across a cell membrane from high to low concentration until equilibrium is reached, type of diffusion
hypotonic solution
low solute
hypertonic solution
high solute
isotonic solution
equal amounts of solute (doesn’t really exist)
cytolysis
when a cell explodes from pressure
turgor pressure (turgid)
cell wall keeps cell from exploding by pushing back (normal)
shrivel
in a hypertonic solution, an animal cell shrivels
plasmolyzed
in a hypertonic solution, a plant cell plasmolyzes
flaccid
plant cells starting to wilt in isotonic solution
osmoregulation
control of water balance and solute concentrations LOOK UP FISH THING
paramecium
pond water, contractile vacuole, ATP
what do human cells do?
pump solutes to try to make an isotonic solution - move the solute and the water will flow
endocytosis
brings IN substrates, 2 types, ATP
pinocytosis
liquids
phagocytosis
solids, sometimes old cells; receptor mediated endocytosis
exocytosis
exporting large particles out, ATP
