transport physiology

Question 1

what is membrane permeability?

Answer 1

the selective passage of hydrophilic solutes across the hydrophobic barrier mediated by the presence of membrane transport proteins

Question 2

what 3 categories can transport proteins be functionally divided into?

Answer 2

channels
pumps
carriers

Question 3

what is electrochemical potential of a solute?

Answer 3

partial molar free energy of the solute or the potential to do work when a difference in electrochemical potential exists across the cell membrane

Question 4

what 3 things determine the electrochemical potential of a solute on either side of the cell membrane?

Answer 4

solute activity (or concentration in dilute solution)
solute charge and valence
electric potential difference across the membrane

Question 5

what is active transport?

Answer 5

movement of solute from place of low to a place of high electrochemical potential

Question 6

what is passive transport?

Answer 6

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

Question 7

what is thermodynamic equilibrium?

Answer 7

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

Question 8

what is the difference for non-electrolytes in thermodynamic equilibrium? what is an example of this?

Answer 8

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
ex. glucose

Question 9

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?

Answer 9

no!

Question 10

what is a capability of active transport that does NOT apply to passive transport?

Answer 10

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

Question 11

what are two examples of passive solute transport?

Answer 11

uniporters and channels

moving things down the gradient

Question 12

where does the energy input come from in primary active transport?

Answer 12

it arises from the hydrolysis of phosphate bonds of ATP

“ion translocating ATPases”

Question 13

where does the energy input come from in secondary active transport?

Answer 13

arises from a coupling to a second solute, moving down its electrochemical potential gradient

Question 14

what type of transport is a symporter?

Answer 14

secondary active transport

Question 15

what type of transport is a antiporter?

Answer 15

secondary active transport

Question 16

what type of transport is a pump?

Answer 16

primary active transport

Question 17

what is non mediated transport?

Answer 17

arises from the transfer of solutes across the membrane without interaction with/mediation by membrane transport proteins
this is simple diffusion

Question 18

how are mediated transport mechanisms distinguished?

Answer 18

by substrate specificity and affinity

Question 19

what type of transport is faster; carrier mediated or channel mediated?

Answer 19

channel mediated

Question 20

what ATPase is most common in the body?

Answer 20

Na/K ATPase

it is present in the plasma membrane of all cells

Question 21

how is the steady state achieved in reguard to the Na/K across the cell membrane

Answer 21

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

Question 22

which one demonstrates the functional property of substrate “saturability”; carrier mediated or simple diffusion?

Answer 22

carrier mediated (or facilitated diffusion)

Question 23

what is the definition of Km regarding substrate saturability? what does a higher Km mean?

Answer 23

Km characterizes the affinity of solute associated-dissociation with the transporter
a higher Km means a lesser affinity

Question 24

what characteristic determines Vmax value?

Answer 24

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

Question 25

when can maximum velocity of transport occur?

Answer 25

• when the solute association and disassociation with the transporter are NOT the rate limiting steps in the process
• or if the transporter is saturated

Question 26

define transport stoichiometry

Answer 26

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

Question 27

what does the property of electrogenicity state?

Answer 27

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