Electrical Properties of Membranes Flashcards
Describe the extracellular and intracellular concentrations of major ions
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
Describe the major difference between active and passive transport of molecules or ions across the membrane
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
Electrochemical Gradient
Aggregate gradient generated by the charge and concentration. It and act cooperatively or antagonistically
What are the 4 types of ion channels?
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
Transporter Proteins
Utilize conformational changes to transport solutes.
Describe the distinct types of active transport in membranes
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.
Uniport
Moves one thing in one direction
Symport
moves two things in the same direction
Antiport
Moves two things in opposite directions
Describe the 3 types of ATP driven pumps
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
P-type pump
They phosphorylate themselves during transport and they transport IONS
F-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
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
Describe ABC transporter’s involvement in disease
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.
Multi-drug resistance protein (MDR)
Pumps numerous drugs out of the cytosol. Expression increased in numerous cancers, making them resistant to drugs targeting them
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. Makes water enter the cell.
Plasmodium Falciparum
Agent of malaria. It utilizes the ABC transporter to pump chloroquine, an antimalarial drug, out of the disease causing protest
Describe the sequence of events in one functional cycle of the Na+/K+ ATPase
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.
Explain the origins of resting potential in the cells. What is the role of Na/K-ATPases? What is the role of K+ channels?
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
Explain the concept of Nernst Potential or the Equilibrium Electrochemical potential for an ion. What forces are in equilibrium at the membrane voltage?
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
Define the directions of positive and negative currents in relation to ions moving across the cell membrane
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.
What determines a negative or positive current in relation to the Nernst Potential of a given ion?
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
Hydrophobic molecules
O2, CO2, N2, Steroid, hormones. These readily diffuse through the membrane
Small uncharged polar molecules
H2O, Urea, glycerol. These diffuse sometimes but usually do not because polar
Large Uncharged Polar Molecules
Glucose, sucrose. These virtually never diffuse through the membrane. Too big
Ions
These never diffuse through the membrane (it would take hours for them to)
