Exam1Lec2TheMembranePotential Flashcards
Membrane consists of ___ and ____
phospholipids, proteins
Membrane has proteins that helps with adaptability to environment and communication of other cells
Phospholipid bilayer acts as a ____ to many solutes
barrier
What provides permeation pathways or act as sensors that relay signals?
Transmembrane proteins
Transmembrane protein function and regulation is the essence of what three factors?
- Cellular communication
- changing cellular fxn by controlling what goes into and out of cell
- events that occur inside cell
Transport across the membrane can take place via
- Diffusion: solutes/species can simply diffuse
- Carrier proteins: provide help for solutes to cross p. membrane b/c too big or charged.
- Ion channels: formed by proteins in lipid bilayer to provide adequate environment for ions
Only ____ and ____ can cross the plasma membrane readily (down concentration gradient)
small, lipophillic
____ and ____ need help to cross the membrane. and ____ provide this help.
Ions, large polar (uncharged) molecules, transpors and ion channels
Which one is quicker, ion channels or transporters?
Ion channels
Explain how ion channels work
They provide an aq space (filled with water) to ions can move
They are transmembrane proteins that allows specific ions to move across the membrane down their electrochemical gradient through an aq pore formed by the channel protein. Usually they require a stimulus such as a ligan binding or a change in membrane potential in order to activate
Explain how transporters work
Have a receptor for a solute to binds. Once it biinds, the transporter changes conformation and opens other side losing affinity for solute and releases it.
What is membrane potential?
Charge gradient producing voltage difference across membrane
a voltage diff exists across the plasma membrane and a second source of free energy acting on charged solutes
Em=Ein-Eout
Typial resting membrane potential is
A.positve
B. negative
C. neutal
negative
How does the charge gradient form?
different ions concentrations and selective permeabilities of those ions create charge gradient which creates membrane potential
Movemnt of ucharged molecules are ____ by the membrane potential
NOT affected
This is bc for ex, you have a cell where inside is neg change, and you put cell in same area as a solure that is uncharged. The solute that is uncharges still moves down concentation grdient and does not care abt voltage diff bc solute is uncharged
Movement of ions are affected by what two things??
Chemical and electrical gradients
Chemical gradient bc there is a difference of concentration b/w inside and outside cell
eletrical gradient bc there is more or less negatice and positve cells inside or outside the cell and they attract each other
What does electrochemical potential mean?
The free energy acting on charged particles
2 forces determine movement of charged particles across the membrane
The nerst eq is used to predict what?
Equilbrium potential for a SINGLE permeable ionic species. It reflects a balance (at equilibrium) b/w chemical and electrical gradients.
What is the nerst equation
Eeq=58/z x (log co/ci)
In this pic, is Ena positive or negative and why?
add pic slide 14
Posititve becuase a large inwards chemical grqdients pulls na into cell. A positive equilibrium constant is needed to balance this chemical gradient to prevent further movement of sodium inside of the cell.
A cation will move into a cell when the membrane potential (Em) is more ____ than the equilibrium potential
negative
Thisis bc as K+ moves inside the cell, the inside cell becomes more positive and Em will start to move to more positve lvs closer to Ek
A cation will move out a cell when the membrane potential (Em) is more ____ than the equilibrium potential
positive
K+ ions would like to move outside of cell to try and drg the Em closer to Ek
Resting neuronal membrane potential is ____ mv
-70
What determines the resting membrane potential?
Na+, K+, Cl- ions
The ____ and ____ of Na+, K+, and Cl- ions set the membrane potential
permeabilities, concentrations
Em wants to be closest to Eeq of ion with the highest ____ at a given time
permeability
Why is Em (-70) closest to Ek (-84)?
At rest Em of cells is mainly permeable to K+ so the Em wants to be close to Ek b/c its the ion with the largest permeability (more K+ ion channels are open compared to rest of ions)
What does the Goldman equation tell us?
It describes the resting membrane potential accounting relative permeabilities and concentration gradients of three primary permeable ions
Permeability of an ion through the plasma membrane is dictated by what?
Ion channels ( high permeability if ion channel is open, low perm is ion channel is closed)
What would cause a change in membrane potential?
Changing internal or external ionic concentations, the largest change in Em occurs when the concentration gradient of the ion of greatest permeability is changed (generally K+)
changing con. gradient and perm of ions
If con of K+ changes detrimental cardiac/neural/muscle conseq can occur,
When external K+ concentration is increased, Em moves to less ____ meaning that the cell is ____.
negative, depolarized
Em shifts with changing K+ concentration
If membrane potential can be estimated from the Goldman equationm then Em will change due to what two factors?
- Changing Co or Ci of the ion with greatest perm (generally K+)
- Changing relative perm of all ions
Em shifts with changes in relative perm, what happens to Em if Pna increases? (Ena=+t67)
Em will be less negative because as Pna incr EM moves toward depolarized potentials
Em moves toward the eq potential of the ion of incr pem
Em shifts with changes in relative perm, Pna increases, then Pna returns to resting values and Pk increases, what happends to Em? (Ek=-84)
Em shifts toward Ek, so it becomes more neg. The membrane potential will repolarize toward negative potentials reaching potentials more hyperpolarized than the resting potential.
What are the 4 major classes of ion channels?
- Leak (constantly active)
- Stretch-activated
- Ligand-gated
- Voltage-Gated
Explain Leak channels
These are active most of the time , providing a permeation path for a specific ion, especially at rest.
Explain Stretch-activated channels
When the plasma membrane is stretched the proteins change conformation where an aq pore is formed.
Cell stretches, ion channels open (change conformation, cell generates action potential
Explain ligand-gated channels
a molecule binds to the protein to activate a channel
A ligand like a neurotransmitter binds to a receptor and the channel opens (channel is ligand gated) and an influx of ions occur
Explain voltage-gated ion channels
channel activated following a change in membrane potential
when voltage across membrane changes, ion channels sense dep and open and close
What is action potential?
Transient changes in membrane potential caused by orchestrated opening and closing of ion channels
The electrochemical potential which is the sum of the chemical and electrical potentials determines what three things?
- Rate
- direction
- extent of movement of charged particles
True or false, the plasma membrane is only permeable to 1 ion.
FALSE, most ions cross the membrane with some permeability
What is the resting membrane potenial? Erest
The combined equilibrium potentials for all permeable ions which is calculated by the Goldman eq using the msot permeable ions (Na, K, Cl)
