Transport

Question 1

basic principles of membrane transport

Answer 1

1. solute electrochemical potential
2. solute electrochemical potential gradient
3. active transport
4. passive transport

Question 2

electrochemical potential of a solute

Answer 2

• partial molar free energy of the solute
• potential to do work when a difference in potential exists across a membrane
• function of solute activity, charge, and valence and the electrical potential difference across the membrane (voltage)

Question 3

difference in electrochemical potential

Answer 3

• reflects magnitude of the difference in transmembrane solute concentration and the difference in trans membrane voltage factored by the charge and valence of the solute
• gradient

Question 4

thermodynamic equilibrium in absence of gradient and DF

Answer 4

-passive transport mediates unidirectional transport in the forward and reverse direction resulting in no net transport

Question 5

thermodynamic equilibrium for anions and cations

Answer 5

• occurs when chemical and electrical DF are equal and opposite
• net movement is zero
• unidirectional solute transport equal and opposite still-no net movement

Question 6

thermodynamic equilibrium for non-electrolytes

Answer 6

• occurs when chemical gradients are equal and opposite
• voltage difference is not a DF like it is for cations and anions
• unidirectional solute transport equal and opposite still-no net movement

Question 7

non-equilibrium steady state

Answer 7

• equilibrium does not equal steady state
• solute in electrochemical disequilibrium but unidirectional solute transport is equivalent
• intra or extra cellular solute electrochemical potential is constant against the opposite site of the membrane (Na kept high outside, but rate of influx and efflux are equal, still inward Na gradient)

Question 8

3D concept of gradient

Answer 8

• difference
• direction
• DF

Question 9

thermodynamic classification of membrane transport

Answer 9

1. passive transport
2. primary active transport-hydrolysis of ATPase
3. secondary active transport- coupled to another transfer of ions and uses that energy- indirectly dependent on ATP hydrolysis, use one gradient energy to make another gradient

Question 10

molecular mechanisms

Answer 10

A. Ion translocating pump (primary active)
B. Channel (passive) (can also be facilitated diffusion)
C. Carrier
-1. uniporter (passive)- faciliated diffusion
-2. symporter, cotransporter (secondary active
-3. antiporter, countertransporter, exchanger (secondary active)-first solute down gradient, second up

Question 11

examples of sym and antiport

Answer 11

• ATPase drives Na out to begin with, then influx of Na back in allows for use of the energy
• sym means Na comes back in with it
• anti means Na comes back in and other molecule goes out

Question 12

non mediated transport

Answer 12

• simple diffusion
• passive
• no protein

Question 13

channel mediated vs uniporter

Answer 13

• both considered facilitated diffusion

- channel can be gated by something- voltage, ligand can shut

Question 14

primary active transport

Answer 14

• ion translocating ATPases, use energy of ATP hydrolysis
• Na/K
• Na out serves as gradient for cotransporters because it wants to come back in
• K in makes membrane neg potential (when coupled with Na gradient makes bigger DF for organic and inorganic solutes to go inside)
• 3 Na out, 2 K in
• net pos out
• steady state of Na because it leaks back and K leaks out

Question 15

functional properties of membrane transporters

Answer 15

• have Km and Vmax (Jmax)
• measures of saturability
• substrate selectivity/specificity
• competitive/ non competitive transport inhibition- does increasing substrate help? if yes- competitive
• stoichiometry
• electrogenicity