Electrical Properties of Membranes

Question 1

Describe the extracellular and intracellular concentrations of major ions

Answer 1

1) Na+: More outside (sodium is pumped out against its gradient)
2) K+: More inside the cell (pumped in against its gradient)
3) Mg2+: More outside cell
4) Ca2+: More outside
5) Cl-: More outside

Question 2

Describe the major difference between active and passive transport of molecules or ions across the membrane

Answer 2

Passive transport is the movement of ions or molecules with its electrochemical gradient and does NOT require ATP. It can be facilitated using channel proteins

Active transport is the movement of ions and molecules AGAINST their electrochemical gradient and REQUIRES ATP

Question 3

Electrochemical Gradient

Answer 3

Aggregate gradient generated by the charge and concentration. It and act cooperatively or antagonistically

Question 4

What are the 4 types of ion channels?

Answer 4

1) Voltage-gated: If voltage changes it can open or close. At different voltages the channel will have a different probability of being open or closed
2) Ligand-gated (extracellular ligand): Ligand binds from outside the cell to open or close it
3) Ligand-gated (intracellular ligand): Ligand binds from inside the cell to open or close it
4) Mechanically Gated: Mechanical pressure can open or close them

Question 5

Transporter Proteins

Answer 5

Utilize conformational changes to transport solutes.

Question 6

Describe the distinct types of active transport in membranes

Answer 6

1) Primary Active Transport: The protein directly uses ATP to push something against its gradient
2) Secondary Active Transport: The protein is indirectly using ATP via another currency source. It is a coupled transporter. It uses energy stored in an electrochemical gradient (usually Na+) to drive cargo against its gradient.

Question 7

Uniport

Answer 7

Moves one thing in one direction

Question 8

Symport

Answer 8

moves two things in the same direction

Question 9

Antiport

Answer 9

Moves two things in opposite directions

Question 10

Describe the 3 types of ATP driven pumps

Answer 10

1) P-type pump: They phosphorylate themselves during transport and they transport IONS

2) F-type (and V-type) proton pump: ATP synthases. They are making ATP from a gradient. Protons move with the gradient to make ATP
V-type proton pump: It hydrolyzes ATP to pump protons against their gradient

3) ABC Transporter: Usually responsible for transporting things that are NOT ions. it hydrolyzes 2 ATP. It is an ATP Binding Cassette (ABC). They transport all things non-ionic but some also transport ions. ATP hydrolysis drive a conformational change in it

Question 11

P-type pump

Answer 11

They phosphorylate themselves during transport and they transport IONS

Question 12

F-type proton pump

Answer 12

ATP synthases. They are making ATP from a gradient. Protons move with the gradient to make ATP

Question 13

V-type proton pump

Answer 13

It hydrolyzes ATP to pump protons against their gradient

Question 14

ABC Transporter

Answer 14

Usually responsible for transporting things that are NOT ions. it hydrolyzes 2 ATP. It is an ATP Binding Cassette (ABC). They transport all things non-ionic but some also transport ions. ATP hydrolysis drive a conformational change in it

Question 15

Describe ABC transporter’s involvement in disease

Answer 15

1) Multi-drug resistance protein (MDR): Pumps numerous drugs out of the cytosol. Expression increased in numerous cancers, making them resistant to drugs targeting them
2) Cystic Fibrosis Transmembrane Conductance Regulator Protein (CFTR): Cl- channel that transports Cl- from the cell. When defective, these ions are trapped in the cell. This attracts more cations in the cell because the electrochemical gradient for these ions changes. More ions in general in the cytoplasm induces water to enter the cell through osmosis. Its departure from the extracellular space induces a thick, pathological mucus, especially in lungs
3) Plasmodium Falciparum: Agent of malaria. It utilizes the ABC transporter to pump chloroquine, an antimalarial drug, out of the disease causing protest
4) Cystinuria: Cystine build up and get kidney stones.

Question 16

Multi-drug resistance protein (MDR)

Answer 16

Pumps numerous drugs out of the cytosol. Expression increased in numerous cancers, making them resistant to drugs targeting them

Question 17

Cystic Fibrosis Transmembrane Conductance Regulator Protein (CFTR)

Answer 17

Cl- channel that transports Cl- from the cell. When defective, these ions are trapped in the cell. This attracts more cations in the cell because the electrochemical gradient for these ions changes. More ions in general in the cytoplasm induces water to enter the cell through osmosis. Its departure from the extracellular space induces a thick, pathological mucus, especially in lungs. Makes water enter the cell.

Question 18

Plasmodium Falciparum

Answer 18

Agent of malaria. It utilizes the ABC transporter to pump chloroquine, an antimalarial drug, out of the disease causing protest

Question 19

Describe the sequence of events in one functional cycle of the Na+/K+ ATPase

Answer 19

1/3 of the energy is devoted to this pump alone. Sodium goes out, Potassium goes in. It is a currency exchanger! It establishes an Na+ gradient. It is a P-type pump because it is phosphorylated.

STEPS:
1) Na+ binding, ATP hydrolysis, phosphorylation of cytoplasmic residues

2) Conformational change, Na+ transfer
3) K+ binding on extracellular face, Dephosphorylation event
4) K+ transfer with the dephosphorylation induces a conformational change and K+ is released in the cell.

Question 20

Explain the origins of resting potential in the cells. What is the role of Na/K-ATPases? What is the role of K+ channels?

Answer 20

The resting potential arises from where the molecules or ions WANT to be. The sodium-potassium pump maintains the resting potential by keeping the inside negative and the outside positive. The K+ leak channels prevent too much accumulation of the K+ in the cell. They also help restore the resting potential in an action potential

Question 21

Explain the concept of Nernst Potential or the Equilibrium Electrochemical potential for an ion. What forces are in equilibrium at the membrane voltage?

Answer 21

The electric and chemical forces are in equilibrium. They are described by the ions wanting to move with its concentration gradient but also its electrical gradient. They are two opposing forces that try to equilibriate

Question 22

Define the directions of positive and negative currents in relation to ions moving across the cell membrane

Answer 22

Positive voltage means a positive current which means that a positive ion will leave the cell or a negative ion will enter the cell.

Negative voltage means a negative current which means that a positive ion will enter the cell or a negative ion will leave the cell.

Question 23

What determines a negative or positive current in relation to the Nernst Potential of a given ion?

Answer 23

The current is defined by the voltage.

DELTA(V) = Vm - Vx

If the Voltage is positive, the current is positive.

If the voltage is negative, the current is negative

Vx = 61.5mV/z * log [Xoutside] / [Xinside]

If Vx is more positive than Vm, than positive X will enter the cell or negative X will leave the cell.

If Vx is more negative than the cell, than a positive X will leave the cell or a negative X will enter the cell

Question 24

Hydrophobic molecules

Answer 24

O2, CO2, N2, Steroid, hormones. These readily diffuse through the membrane

Question 25

Small uncharged polar molecules

Answer 25

H2O, Urea, glycerol. These diffuse sometimes but usually do not because polar

Question 26

Large Uncharged Polar Molecules

Answer 26

Glucose, sucrose. These virtually never diffuse through the membrane. Too big

Question 27

Ions

Answer 27

These never diffuse through the membrane (it would take hours for them to)