cell membrane and tonicity Flashcards
the cell membrane is arranged as a
phospholipid bilayer
cell membrane serves as a
cellular barrier/border
how permeable is the cell membrane?
selectively permeable
the heads of the phospholipids are
polar
hydrophilic
the tails of the phospholipid bilayer are
nonpolar
hydrophobic
the middle of the phospholipid bilayer is impermeable to
polar molecules
when the membrane is fluid, the bilayer is
unsaturated with hydrocarbon kinks
when the membrane is viscous, the bilayer is
saturated hydrocarbon tails
cholesterol acts as a
fluidity buffer
what is the purpose of cholesterol in the cell membrane
resists changes in fluidity as temp changes
how often do phospholipids move laterally in the cell membrane?
10^7 times per second
how often do phospholipids flip flop in the cell membrane?
once per month
where are the hydrophobic regions of a protein in the phospholipid bilayer?
by the tails of the phospholipids
where are the hydrophilic regions of a protein in the phospholipid bilayer?
by the heads of the phospholipids
membrane proteins determine
membrane’s specific functions
6 major functions of membrane proteins
Transport
Enzymatic activity
Signal transduction
Cell-cell recognition
Intercellular joining
Attachment to the cytoskeleton and extracellular matrix (ECM)
peripheral proteins
loosely bound to surface of membrane
integral proteins
penetrate lipid bilayer, usually across whole membrane
(transmembrane protein)
2 types of transport
passive
active
3 types of passive transport
diffusion
facilitated diffusion
osmosis
does passive diffusion require energy
no
does active diffusion require energy
yes
simple diffusion
Move from HIGH to LOW concentration
“passive transport”
no energy needed
Solute moves DOWN concentration gradient until reaches equilibrium
What molecules CAN get through the phospholipid bilayer directly?
fats & other lipids, hydrocarbons, CO2, Oxygen, hydrophobic molecules
What molecules CANNOT get through the phospholipid bilayer directly?
polar molecules (H2O)
ions (charged) (salts, ammonia)
large molecules
(starches, proteins)
transport proteins
facilitates = to help
uses proteins to help
no energy needed
channel proteins
embedded in the cell membrane & have a pore for materials to cross
carrier proteins
can change shape to move material from one side of the membrane to the other
osmosis
Diffusion of water from
HIGH concentration of water to
LOW concentration of water
across a
semi-permeable
membrane
3 types of solutions
hypertonic
isotonic
hypotonic
how is direction of osmosis determined
by comparing total solute concentrations
hypertonic
more solute
less water
water moves out
hypotonic
less solute
more water
water moves inside cell
isotonic
equal solute and water
equillibrium
cell survival depends on balancing
water uptake and loss
animal cells in freshwater in hypotonic solution - problem and solution
cell gains water, swells & can burst (cytolysis)
contractile vacuole
pumps water out of cell
ATP
plant cells in freshwater in hypotonic solution - problem and solution
no problem
normal
cell wall prevents from bursting
becomes turgid (full) with water
turgor pressure
pressure that builds up, gives plant shape
purpose of a contractile vacuole
forces out excess water
animal cells in salt water in hypertonic solution - problem and solution
cell loses water and can die
take up water or pump out salt
plant cells in salt water in hypertonic solution - problem and solution
no problem
plasmolysis, wilts
can recover
plasmolysis
loss of water, decreasing turgor pressure causing wilting
only in plant cells
crenation
animal cells shrivel up
animal cells in mild salt solution in isotonic solution - problem and solution
no problem
no net movement of water
flows across membrane equally, in both directions
cell in equilibrium
volume of cell is stable
plant cells in isotonic solution
flaccid, wilts
Hypertonic or hypotonic environments create
osmotic problems for organisms
Osmoregulation
the control of water balance
a necessary adaptation for life in such environments
aquaporins
small transmembrane proteins that facilitate the rapid transport of water across cell membranes through a pore, in and out of cells
