Flashcards in transport physiology Deck (27)
what is membrane permeability?
the selective passage of hydrophilic solutes across the hydrophobic barrier mediated by the presence of membrane transport proteins
what 3 categories can transport proteins be functionally divided into?
what is electrochemical potential of a solute?
partial molar free energy of the solute or the potential to do work when a difference in electrochemical potential exists across the cell membrane
what 3 things determine the electrochemical potential of a solute on either side of the cell membrane?
solute activity (or concentration in dilute solution)
solute charge and valence
electric potential difference across the membrane
what is active transport?
movement of solute from place of low to a place of high electrochemical potential
what is passive transport?
movement of a solute from a place of high electrochemical potential on one side of the cell membrane to a place of lower electrochemical potential on the opposite side
what is thermodynamic equilibrium?
occurs when the chemical and electrical driving forces acting on solute transport are equal and opposite in direction across the membrane such that the net driving force is zero
what is the difference for non-electrolytes in thermodynamic equilibrium? what is an example of this?
an electrical driving force does not apply here and the thermodynamic equilibrium occurs in the absence of a solute concentration gradient where the transmembrane solute concentrations are equal
would a passive transport mechanism mediate the net transport of a charged solute in a direction across the cell membrane that opposed both the chemical and electrical driving forces acting on the ion?
what is a capability of active transport that does NOT apply to passive transport?
the ability to generate and maintain an electrochemical or chemical potential difference for ions and nonelectrolytes across the cell membrane
this allows for a non-equilibrium solute steady state
what are two examples of passive solute transport?
uniporters and channels
moving things down the gradient
where does the energy input come from in primary active transport?
it arises from the hydrolysis of phosphate bonds of ATP
"ion translocating ATPases"
where does the energy input come from in secondary active transport?
arises from a coupling to a second solute, moving down its electrochemical potential gradient
what type of transport is a symporter?
secondary active transport
what type of transport is a antiporter?
secondary active transport
what type of transport is a pump?
primary active transport
what is non mediated transport?
arises from the transfer of solutes across the membrane without interaction with/mediation by membrane transport proteins
this is simple diffusion
how are mediated transport mechanisms distinguished?
by substrate specificity and affinity
what type of transport is faster; carrier mediated or channel mediated?
what ATPase is most common in the body?
it is present in the plasma membrane of all cells
how is the steady state achieved in reguard to the Na/K across the cell membrane
it results from balancing the "leak" of Na into the cell and K out of the cell with active transport of Na and K in the opposite direction by the Na/K ATPase
which one demonstrates the functional property of substrate "saturability"; carrier mediated or simple diffusion?
carrier mediated (or facilitated diffusion)
what is the definition of Km regarding substrate saturability? what does a higher Km mean?
Km characterizes the affinity of solute associated-dissociation with the transporter
a higher Km means a lesser affinity
what characteristic determines Vmax value?
determined by the number of transporters present in the membrane and the time required for the transporter to undergo one complete transport cycle or turnover
when can maximum velocity of transport occur?
-when the solute association and disassociation with the transporter are NOT the rate limiting steps in the process
-or if the transporter is saturated
define transport stoichiometry
the number of substrate molecules transported in one complete cycle of molecular events mediated by the transport protein and resulting in transfer of substrate across the membrane