transport Flashcards
what types of molecules is the cell membrane impermeable to?
large and/or charged molecules
what is the electrochemical potential of a solute?
partial free energy of the solute or the potential to do work when a difference in potential exists across a membrane
what influences a solute electrochemical potential?
solute concentration, solute charge and valance, and the electrical potential difference across the membrane
when do trans membrane electrical potential differences have an effect on a solute electrochemical potential?
when it is charged
what is active transport?
movement of solute from a low electrochemical potential to a place of higher potential across a membrane (requires energy)
what is passive transport?
movement of solute along its electrochemical potential gradient (no energy required)
what is thermodynamic equilibrium? is solute exchange stopped?
the absence of a solute electrochemical potential difference across a membrane. There is passive solute exchange in both directions with no net transportation
how are the goals of passive and active transport different?
active transport generates and maintains an electrochemical or chemical potential difference across a cell membrane while passive transport does not
what is a non-equilibrium solute steady state and how is it maintained?
concentration of solutes and voltage is not the same across a membrane. maintained by active transport
what are the three Ds of gradients?
difference, direction and driving force
what are the types of passive transport?
diffusion, channels and uniporter carriers
what is the difference in primary and secondary active transport?
primary couples movement with hydrolysis of ATP. Secondary couples movement with the passive diffusion of a second solute that drives transport (still indirectly dependent upon ATP hydrolysis)
what are the two types of secondary active transport mechanisms?
symporters (move both molecules in the same direction) and antiporters (moves two molecules in different directions)
what is the only instance of non mediated transport?
simple diffusion
what is the only instance of primary active transport?
pumps
what are two examples of facilitated diffusion? which is faster?
channels and uniporters. channels are faster
how do uniporters transfer solute into or out of a cell?
they associate with a solute, undergo a conformational change and release the solute on the other side of the membrane.
do primary active transporters have to only move one solute?
no, it can move two in opposite directions (ex: Na/K pump)
what causes the gradient that is capitalized by secondary active transport?
primary active transport forms the gradient that it utilizes
what is the rate of transport across a cell membrane dependent upon?
solute concentration on the side that the solute originates
what is the difference in the rate of transport between simple diffusion and facilitated diffusion?
simple diffusion has a rate that increases linearly with increased solute. facilitated diffusion has a maximum rate and is saturable (looks like an enzyme curve)
what is characterized by Vmax and Km in solute transportation?
Vmax is the maximal rate of solute transport
Km is the solute concentration when v=1/2Vmax (characterizes the afinity of solute association/disassociation with the transporter)
what is the Vmax of a transporter controlled by?
the rate limiting step in the transport process and the number of transporters
when can Vmax and Km be different for the same transporter?
when it is transporting different solutes
what other aspects of enzyme kinetics apply to transporters?
inhibition (competitive, noncompetitive)
what types of transporters control pH in the cell?
acid etruders (remove H+) and acid loaders (bring in H+)
other than transport of H+, how is pH controlled by the cell?
efflux and influx of HCO3
what is transport stoichiometry?
number of substrate molecules transported in one complete cycle of molecular events mediated by that protein
how is electrogenicity achieved?
movement of unequal charges across the cell membrane
