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Flashcards in Transport Physiology Deck (17):

What is non-equilibrium steady state?

When a solute is in electrochemical dis-equilibrium across the cell membrane but unidirectional solute transport is equivalent. Na as an example in cells where the Na/K ATPase keeps concentrations constant inside the cell.


What are the thermodynamic transport mechanisms?

Passive Transport
Primary Active transport
Secondary active transpor


What are the molecular mechanisms of transport?

Ion-Translocating pump (primary active)
Channel (passive)
Carrier - Uniporter (passive); Symporter, Cotransporter (Secondary Active; Antiporter, countertransporter, exchanger (secondary active)


Describe what makes a primary active transporter

Primary active transport mechanisms include the ion-translocating ATPases or "pumps" which are directly dependent upon and transduce the energy released from ATP hydrolysis into the potential energy stored in the formation and maintenance of an ion electrochemical potential gradient. (i.e. Na/K-ATPase, H/K-ATPase, Ca-ATPase etc.)


Describe a secondary active transporter

these include symporters and anti porters which are indirectly dependent upon the nervy released from ATP hydrolysis. The result is one solute moving down its electrochemical potential gradient driving or pushing the second solute up or against its electrochemical potential gradient. (ie. Na-glucose symporter etc.)


Non-mediated transport includes:

Simple diffusion only (passive). Non-mediated transport arises from the transfer of solutes across the membrane without interaction with, or mediation by, the presence of membrane transport proteins.


Mediated Transport includes:

Channels, carriers and pumps.


What are three examples of carriers and explain if they are passive, primary active, or secondary active:

Facilitated diffusion (uniporter) - passive
Cotransport (symporter) - Secondary active
Countertransporter (antiporter) - Secondary active


Channels always facilitate _____ transport?

Passive transport. Channels differ from facilitated diffusion (a carrier mediated transport) in specificity, rate, and capacity of solute transport.


Pumps always facilitate ______ transport?

Primary active


What is the general difference between channel-mediated transport and carrier-mediated transport?

Channels mediate a rate of transport of inorganic ions many orders of magnitude faster than the rate of transport of organic solutes by carrier-mediated facilitated diffusion. Channels can be ligand gated, voltage gated etc.


How is the Na/K-ATPase function essential for intracellular homeostasis? 2 Na in for 3 K out. Leads to what charge distribution?

The inward Na concentration gradient created serves as the major driving force for secondary active transport of essential metabolites. The outward K garden generates the inside negative voltage difference which makes the inward Na electrochemical potential gradient a much larger driving force than it otherwise would be.


Describe the shapes of the graphs for Jx vs. [X] for simple diffusion and carrier-mediated (or facilitated diffusion)?

Simple diffusion is a straight line. Carrier-mediated looks like an enzyme kinetics curve. There is a similar formula and Km can be calculated. At low concentrations it is linear but as concentration goes up it becomes logarithmic. The curve shows a "satiability" common to all mediated transport mechanisms.


Functional properties of membrane transporters include:

1 Kinetics
2 Substrate Selectivity/ Specificity
3 Competitive and/or Noncompetitive Transport Inhibition
4 stoichiometry
5 electrogenicity


What are two ways membrane transporters may be distinguished functionally and further classified?

1 By which substrates are transported by a particular transport protein.
2 By which substrates inhibit transport either competitively or non competitively.


Describe the property of electrogenicity

It confers membrane potential difference (voltage) as well as substrate concentration difference as an additional driving force favoring or opposing transport.


An excess of acid in the cell is termed _____ while a deficit of acid is termed _____

Acidosis. Alkalosis