Membrane transport Flashcards
what are three methods of solute transport across cell membranes
- passive/non-carrier mediated
- passive/carrier mediated
- active
three examples of passive non carrier cell transport
- simple diffusion across the cell membrane
- simple diffusion through pores
- simple diffusion through gated channels
what is an example of carrier mediated transport
facilitated diffusion
what are three methods of active solute transpoirt
- active transport requiring ATP
- active transport using energy from redox reactions
- secondary active transport
osmosis
the diffusion of water across a cell membrane
what happens in secondary active transport
two simultaneous movement of two link substances across a cell membrane
two types of secondary active transport
- symport
- antiport
symport
coupled transport where the linked substances move in the same direction
antiport
coupled transport where the two substances move in opposite directions
what types of solutes are capable of simple diffusion? examples (3)
solutes must be uncharged and hydrophobic
- gasses
- steroid hormones
- anesthetics
what is the driving force behind simple diffusion
the concentration gradient on either side of the cell membrane
define all variables
R = ideal gas constant (.002kcal/mol)
T = temp in Kelvin (310 in humans)
Xi = intracellular fluid concentration of X
X0 - extracellular fluid concentrationof X
flux
the number of moles of a solute that cross a unit area of a membrane per unit of time (moles/cm2 * s)
what is ficks first law of diffusion
flux will move from areas of high concentration to areas of low concentration
what two factors determine the amount of flux (diffusion)
- permeability of the membrane to X
- magnitude of the gradient fo X across the membrane
pores
intergra membrane proteins that for conduits that are always open
channell
a gated pore that can be opened or closed
describe the variables and what this equation means (3)
- the electrochemical difference is the the driving force behind passive diffusion
- the electrochemical difference is the sum of the chemical energy difference and electrical energy difference
- z = valence of the ion, F = .023kcal/mol *mV, psi1 - psi0 = the membrane potential
describe the variables
- E si the equilibrium potential for the ion
- R is the ideal gas constant
- T is the temperature in kelvin
- Xi is the ICF solute concentration
- Xo is the ECF solute concentration
- zx is the valence of electron x
- F is Farraday constant
what are six steps in passive membrane transport through integral membrane proteins
- the carrier protein is open
- x enters the protein and bind to the binding site
- outer gate closes and x becomes trapped in the protein
- inner gate opens with x still bound
- X exits the inside of the cell
- the outer gate closes, occluding the empty binding site
primary active transport
solute movement against electrochemical gradiant that requires energy
what are two sources of energy for primary active transport
- ATP hydrolysis
- directly from a primary metabolic reaction
aquaporins
specialized water channels in the cell membrane
what are two types of cells that always have aquaporins (AQP1)
- RBCs
- Renal proximal convoluted tubule
what is an example of a cell that places aquaporins based on hormonal control
cells in the renal collecting duct in response to ADH
why is it impractical to measure the concentration of water
because there is too mich water to be accurate
what is the relationship between solute concentration and water concentration
as solute concentration goes up water concentration goes down
Gibbs-Donnan effect
the effect of a charged membrane on charged particles, leading to unequal distribution of ions across the membrane
why must animal cells perform osmotic work
because animal cells swell rather than increase osmotic pressure as water enters and must pump water out of the cell
when does osmotic work occur
during active transport with the Na/K pump
osmolality
the total number of osmotically active solutes in a solution
tonicity
the comparision of effective osmolalities between two solutions seperated by a membrane
what happens to the ECF and ICF with an infusion of isotonic saline
ECF increases with no increase in ICF because there is no change in osmolality
what happens to ECF and ICF with an infustion of solute free water
the ECF experiences an intial decrease in osmolality, causing solutes to diffuse out of the ICF to restore equalibrium
what happens to ECF and ICF with an infusion of NaCl
ECF experiences an increase in osmolality, causing solute to difuse into the ICF
why is epithelial transport important to homeostasis
it controls the composition of interstitual fluid through membrane transport between the body and environment
two places where epithelial transport takes place
- apical membrane
- basolateral membrane
three parts of the apical membrane
- brush border
- mucosal membrane
- luminal membrane
two parts of the basolateral membrane
- serosal membrane
- peritubular membrane
apical membrane
the cell surfaces that face inward toward a lumen
basolateral membrane
the epitheial cells surfaces that face adjacent cells or toward the underlying connective tissue
two epithelial transport membrane
- transcellular
- paracellular
transcellular epithelial transport
substances crosses the cell by going through the apical and then basolateral membranes
paracellular epithelial transport
substances bypass the cell and cross epithelium through cell junctions
two types of epithelial cell junctions
- tight
- leaky
tight epithelia
cell junctions that maintain large ion concentration and osmotic gradients
four examples of tight epithelia
- distal portion of the distal convoluted tubule
- collecting duct
- large intestine
- urinary bladder
leaky epithelia
cell junctions cannot maintain large gradients and are used for bulk transport of solute and water
two examples of leaky epithelia
- small intestine
- proximal convoluted tubule
where are the Na/K pumps located
the basolateral membrane
what is the function of the Na/K pumps
the keep a large inward Na gradient to drive secondary active transport
what happens to most of the K brought into the cell from the Na/K pump
it is recycled through the basolateral membrane via K channels
flow
movement of matter
flux
diffusion
current
the flow of charged particles
how can we increase current, flow, or flux
increase the driving force or decrease the resistance
what is a simple way the body can regulate function
by regulation of current flux and flow
T/F passive transport does not involve energy
false, passive transport releases energy
in terms of energy, what direction does diffusion move
from high energy to low energy
from an energy standpoint, what is a concentration gradient
store potential energy
what is the largest energy expenditure in basal metabolism
the Na/K pump
what is the driving force of simple diffusion
the chemical energy difference on each side of the concentration gradient
resting membrane potential for a neuron
-70mV
what is the charge inside the cell? why
negative, because the positive sodium is pumped out
why is the resting membrane potential of a cell relevant to diffusion
because it is negative, so positive ions are pulled into the cell, and the concentration pushes sodium into the cell
based on chemical energy and concentration, where will potassium be driven in the cell
it will depend on if the chemical energy is overcome by potential energy of the concentration gradient
what direction does a negative delta G move
into the cell
what direction does a positive delta G move
out of the cell
what is the nerst equation and what is it used for
used to determine the equilibrium concentration of an ion
what is used to determine the concentration gradient
the ideal gas law
what is used to determine the electrochemical gradient
why does a cell do osmotic work
to counter act donnan forces that move ions into the cell
