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
