Membrane Transport and Osmosis

Question 1

Define membrane potential

Answer 1

a separation of electrical charge across the plasma membrane of most cells in which that force generated can influence the movement of ions through their channels
- aka electric potential difference

Question 2

Electrochemical gradient

Answer 2

provided by the concentration and electrical differences of the ions on both sides of the membrane which determine the direction and magnitude of ion movement

Question 3

Resting membrane potential

Answer 3

a cell’s electric potential difference at rest
- NEGATIVE in most cells (~-77mV)

Question 4

Channels

Answer 4

integral membrane proteins that span across the lipid bilayer that allow charged ions to cross the membrane
- Can be a single protein with a hole (depending on its conformation)
OR several proteins arranged together where a pore is in the middle
- FAST ion transport (millions per second)

Question 5

Ion Channel Selectivity

Answer 5

Determinants:
- channel diameter
- polarity/charge of the proteins at the walls of the channel
- # of water molecules associated with that ion

Question 6

Channel Gating

Answer 6

open/closed conformations of ion channels allow ion movement on both sides when open
- regulation of ion movement

Question 7

Voltage-gated Ion Channels

Answer 7

channel opens/closes in response to changes in membrane potential

Question 8

Ligand-Gated Ion Channels

Answer 8

channel opens upon binding of a ligand; once ligand binds a conformational change occurs in the channel that opens it up and lets the ion through

Question 9

Leak (Always Open) Channels

Answer 9

channel stays open; play MAJOR role in resting membrane potential

Question 10

Mechanically- Gated Ion Channels

Answer 10

channel opens/closes in response to pressure differences of the membrane

Question 11

Transporters

Answer 11

membrane proteins that mediate movement of a larger variety of particles but exhibit chemical specificity for their ligand; SLOW (10,000s ions per second) d/t bigger conformational change requirement and can become saturated

Question 12

Limitations to Transporter-Mediated Transport

Answer 12

• # of transporters
• speed of conformational change
• solute concentration
• transporter affinity for the solute

Question 13

Primary Active Transport

Answer 13

transport of molecules across membrane that requires ATP (3 major ATPases)

Question 14

Na+/K+ ATPase Pump

Answer 14

Drives 3Na+ OUT of the cell and 2K+ INTO the cell; the reason why the concentrations of these two ions are diff in and out of the cell

Question 15

3 Main ATPases

Answer 15

Na+/K+ ATPase Pump, H+/K+ ATPase Pump, Ca2+ ATPase Pump

Question 16

Secondary Active Transport

Answer 16

active transport of molecules that takes advantage of the gradient; INDIRECTLY uses ATP

Question 17

Co-transport

Answer 17

transport of ion that takes advantage of established electrochemical gradient to drive movement DOWN the concentration gradient; coupled with transport of another molecule (SGLT1 and 2= sodium dependent glucose transporters); INDIRECT use of ATP

Question 18

Counter transport

Answer 18

transport of ion that takes advantage of established electrochemical gradient to drive movement UP/AGAINST the concentration gradient; INDIRECT use of ATP

Question 19

ABC Transporters

Answer 19

subset of primary active transporters; have a variety of substrates

Question 20

Osmosis

Answer 20

the simple diffusion of water from high to low water concentration or low to high solute concentration

Question 21

Aquaporins

Answer 21

membrane protein that mediates osmosis; specialized channels in all cell types

Question 22

Semi-permeable membrane

Answer 22

membrane that only allows water to pass through not solutes

Question 23

Osmotic Pressure ( Π)

Answer 23

the pressure that EXACTLY balances the osmotic water movement that results in a net water flow of ZERO
- the higher the solute concentration the GREATER the osmotic pressure because more water is needed to establish equilibrium between the two compartments
- equation:
Π= (Cs)RT

Question 24

Hydrostatic pressure (P)

Answer 24

pressure exerted by a fluid at equilibrium due to the force of gravity
- equation:
P=Π= (Cs)RT

Question 25

Nonpenetrating (effective) solute

Answer 25

a substance that CANNOT cross the cell membrane and is EFFECTIVE at generating osmotic pressure (i.e Na+, glucose, proteins) so DOES affect cell volume

Question 26

Penetrating (ineffective) solute

Answer 26

a substance that CAN cross the cell membrane and is NOT EFFECTIVE at generating osmotic pressure (i.e urea) so does NOT affect cell volume

Question 27

Isotonic solution

Answer 27

same concentration of nonpenetrating solutes as normal extracellular fluid

Question 28

Hypertonic solution

Answer 28

concentration of solute OUTSIDE of the cell is greater so water LEAVES the cell to reach equilibrium and cell SHRINKS

Question 29

Hypotonic solution

Answer 29

concentration of solute INSIDE of the cell is greater so water ENTERS the cell to reach equilibrium and cell SWELLS

Question 30

Reflection coefficient (σ)

Answer 30

ability of solute to remain “intact” once they cross the membrane; Πeff = σ RT Cs
- ranges 0 ≤ σ ≤ 1
(i.e σ for a solute that can cross the membrane the easiest =0 because it will diffuse right away- like urea)

Question 31

Osmolarity

Answer 31

the actual concentration of solute particles
and is independent of any membrane

Question 32

Tonicity

Answer 32

describes a solution in terms of whether the volume of an immersed cell stays the same (ISOTONIC) or increases (HYPOTONIC) or decreases (HYPERTONIC