1 2 Membrane Transport: Passive and Active Flashcards
___, like ___ and ___ are highly lipid soluble and easily pass though the PM
gasses like oxygen and carbon dioxide
lipid bilayer is made of
phospholipids with hydrophlic heads and hydrophobic fatty acid tails (the lipid part is in the middle)
e.g. of intrinsic membrane proteins
ion channels, water channels, transporters, hormone receptors, cell surface antigens
intrinsic membrane proteins have _____ amino acid regions which are tucked within the alpha helix
hydrophlic
these are tucked inside since they are running through a hydrophobic region (the membrane)
movement in the bilayer (2 examples)
axial rotation
lateral diffusion
e.g. extrinsic/peripheral proteins
proteins of the cytoskeleton
extrinsic protein features
do not span the membrane
attachment occurs via ionic interactions to membrane phospholipids or intrinsic proteins
carbohydrates are on the ___ surface of the membrane
extracellular
role of monosaccharides on the PM
cell recognition/determining receptor specificity
passive transport: definition, examples
substance is transported down its electrochemical gradient and no energy is required
simple diffusion, facilitated diffusion
active transport: definition, examples
substance is transported against its electrochemical gradient and requires energy (ATP)
primary active transport, secondary active transport
all transport except for ____ needs a carrier molecule
simple diffusion
3 characteristics of carrier mediated transport
saturation
stereospecificity
competition
saturation
limited number of binding sites on carrier proteins (transport maximum or Tm)
which type of diffusion does not care about stereospecificity
simple diffusion
competition
structurally similar solutes compete for the same site
is simple diffusion saturable?
no
Km =
solute concentration which gives half the maximal transport rate
simple diffusion
non-carrier mediated transport down an electrochemical gradient
FLUX, J
the rate of net diffusion of solute molecules
the amount of solute moving across a unit area of membrane per unit of time
flux depends on 5 things
concentration gradient across the membrane thickness of the membrane lipid solubility of the solute diffusion coefficient permeability of a solute
oil water partition coefficient (K)
oil / water
the higher it is, the greater the lipid solubility
diffusion coefficient (D)
the larger the molecule and more viscous the medium, the lower the D
permeability
P = KD / membrane thickness
flux formula
J = P (C1-C2)
permeability constant * diff in conc of solute across the membrane
in the flux equation, as long as C1 > C2, that means
there is net movement of solute from side 1 to side 2 of the PM
once equilibrium has been reached, this is considered ___ ___ flux of solute
no net flux
formula for the total amount of solute diffusing across an entire membrane into a cell
flux formula times the area of the membrane
= PA (C1-C2)
the rate at which an uncharged solute (non-electrolyte) diffuses across the cell membrane is dictated by its ____ and _____
lipid solubility and molecular size
are bigger or smaller molecules faster at diffusing through the PM?
smaller
which form of a weak acid/base can diffuse across the membrane?
the un-dissociated form
they can get “trapped” if the pH changes and they dissociate
facilitated diffusion
how lipid insoluble stuff gets across the membrane without using energy
facilitated diffusion is different from simple diffusion b/c (4 things)
- allows much more solute to be transported
- is saturable
- is solute specific
- competition is involved
ion channels (4 things)
- passive (driven by electrochemical gradient)
- regulated (channels open and close)
- three magnitudes faster than facilitated diffusion
- for electrical signaling and secretory processes
facilitated diffusion is for the movement of
sugars and amino acids
active transport
requires energy
moves things against a chemical or electrochemical gradient
primary active transport
directly coupled to an energy producing reaction
i.e. sodium pump (Na/K ATPase)
inhibitors of the sodium pump (2)
cardiac glycosides: ouabain and digoxin
these also inhibit secondary active transport
for each molecule of ATP, ___ Na ions are pumped out and ____ K ions are pumped in
3 Na out
2 K in
two other examples of primary active transport
Ca2+ ATPase - pumps Ca2+ out of cytoplasm
H+-K+ ATPase
secondary active transport
NOT directly coupled to an energy producing reaction but instead depends on the primary active transport of sodium
secondary active transport depends on the primary active transport of this ion
Na+
there are two types of secondary active transport
1/ symport or co-transport
2/ antiport/countertransport/exchange
symport/co-transport
all solutes move in the same direction across the cell membrane
the uphill solute moves in the same direction as sodium, so INTO THE CELL
antiport/countertransport/exchange
uphill solute moves in the opposite direction to the sodium
sodium moves into the cell down its gradient
the solute here moves out of the cell AGAINST its gradient (the solute conc is high outside and low inside)
aquaporins
the holes water travels through across a membrane
osmosis
movement of water across a semi-permeable membrane as a result of the difference in the concentration of particles of a solute that is unable to pass across the membrane
water moves from the solution with the lowest to the solution with the highest concentration of particles
_____ ______ is the driving force for osmosis
osmotic pressure
in osmosis, the movement of water continues until the ____ pressure opposes the osmotic pressure
hydrostatic pressure (column of water)
osmolarity
the number of solute particles present in a solution
osmoles
= n x moles
n = number of particles from each molecule
concentrated solutions have ____ osmolarity
higher
concentrated solutions have ____ osmotic pressures than dilute solutions
higher
water moves from ____ to _____ osmotic pressures across a semipermeable membrane
lower to higher
osmotic pressure is proportional to _____ concentration
solute
osmotic pressure depends on total _____ of the solution
osmolarity
iso-osmotic solution
isotonic - no swelling or shrinkage occurs
hypotonic solution
surrounding environment is less concentrated, so water swells into the more concentrated cell and swells it
(more dilute solutions cause bursting)
hypertonic solution
surrounding environment is more concentrated, so water inside the cell rushes out, causing the cell to shrink and shrivel
what happens to a cell when the sodium pump is not working?
Na+ is not pumped out, so water rushes in, causing the cell to swell
