membrane dynamics Flashcards
the ___ _____ is a selectively permeable barrier between the ECF and ICF
cell membrane
the extracellular fluid consists of:
interstitial fluid and plasma
what is a concentration gradient?
movement of water across a membrane in response to a solute
osmotic pressure
the pressure that must be applied to the more concentrated solution in order to oppose osmosis
Osmolarity describes:
the number of particles in solution.
it takes into account dissociation of molecules in solution.
osmolarity is a _____ property. Which means:
colligative; it depends solely on the number of particles per liter of solution (not size of particles)
Tonicity
describes how cell volume would change if placed in solution
Does tonicity describe osmolarity?
no. it does not have units, it is always comparative
tonicity depends on _____, not just on osmolarity
nature of solutes
penetrating solutes
can enter cell
they are non-polar (urea, glucose (slowly penetrating))
non-penetrating solutes
cannot enter the cell (sucrose, NaCl)
how do you determine tonicity?
determine relative concentrations of non-penetrating solutes in solution an din cell.
tonicity of a solution is:
the effect the solution has on cell volume.
isotonic
a solution that has the same concentration of non-penetrating solutes as normal body cells.
no osmosis occurs.
hypotonic
a solution that has a lower concentration of non-penetrating solutes compared to normal body cells.
what will happen to cells in a hypotonic solution?
water will enter the cells and they swell and rupture (water in IV)
hypertonic
a solution that has a higher concentration of non-penetrating solutes compared to normal body cells.
what will happen to cells in a hypertonic solution?
water will leave the cells and they shrink and crenate (diarrhea)
isosmotic
same concentration in solution and cell
what are the properties of diffusion?
passive processe
moves from high concentration to low concentration (concentration gradient)
continues until concentration is equal (equilibrium)
rapid over short distances
directly related to temperature
inversely related to molecular weight and size
what are the factors affecting rate of diffusion through a cell membrane?
lipid solubility molecular size concentration gradient membrane surface area composition of lipid layer
ficks law of diffusion
rate of diffusion=surface area x concentration gradient x membrane permeability
what are the different types of channels?
water channels (aquaporens) ion channels open (leak) channels Gated Channels
what are the different types of gated channels?
chemically (ligand) gated channels
voltage gated channels
mechanically gates channels
chemically gates channels
there is usually some smaller molecule that which bind to receptors and open the gate
mechanically gates channels
activated by touch or stretch receptors
gated channels
open and close in response to signals
open channels (pores)
are usually open
channel proteins
create a water filled pore
carrier proteins
never form an open channel between the two sides of the membrane
uniport carriers
transport only one kind of substrate
symport carriers
more two or more substrates in the same direction across the membrane
Antiport carriers
move [diff] substrates in opposite directions
how is facilitated diffusion accomplished?
by means of carrier protein
facilitated diffusion are always going from____ to ____ concentration
high to low
why is there always a concentration gradient for glucose?
because cells burn up the glucose once its in the cell. They phosphorylate it and so glucose concentrations are always kept low in the cell and there is always a concentration gradient.
Sodium-Potassium pump
Antiport
uses energy from ATP to pump Na+ out of the cell and K+ into the cell
extracellular fluid:
high in Na+
low in K+
intracellular fluid
Low in Na+
high in K+
what is the mechanism for the Na+K+ pump?
three Na+ will bind from ICF into the transport proteins at high affinity sites which creates a slight negative charge
then ATPase is phosphorylated with P from ATP which changed the shape and allows the Na+ to leave the protein bc it loses it’s affinity.
2K+ then enter the transport at high affinity sites. the phosphate group leaves, changing the protein shape back to its original conformation. the K+ is then released bc the protein again loses its affinity and it all starts all over again.
So, when it’s open towards the ICF, it attracts Na. When it is open toward ECF, it attracts K+
what does it mean to be a sodium dependent transporter?
you need sodium to transport. Na is used to reabsorb everything
which are nonsodium-dependent transporter?
H+
HCO3-Cl-
what is the mechanism for the SGLT (NaGlu trans)?
the concentration gradient drives Na into the transport. Once Na is bound it creates a high affinity site for glucose.
The glucose binding changes the conformation of the carrier so that it is now open facing the ICF. Na is then released into the cytosol and the release changes the glu binding site to low affinity so that glucose is then released.
transport maximum
the max speed to get elements through the membrane. It’s as fast as you can close and open it. It is determined by the number of channels and how fast they open and close.
how is carrier mediated transport competitive?
there are competitive inhibitor like maltose (2 glu) which will bind to the transporter and inhibit Glu from binding. Maltose itself is not carried across the membrane but it keeps glu from crossing. So when other glucose containing molecule are present the rate of glucose transport goes down.
how can carrier mediated transport be saturated?
transport can reach a maximum rate when al the carrier binding sites are filled with substrate.
what are different types of vesicular transport?
phagocytosis
endocytosis
exicytosis
phagocytosis
cell engulfs bacterium or other peptide into phagosome. its a type of endocytosis
endocytosis
membrane surface tension indent and forms vesicles
this is an active process that can be nonselective or highly selective
receptor mediates endocytosis uses coated pits (membrane recycling)
caveolae
what is the first step in phagocytosis?
the phagocytic whit blood cell encounters a bacterium that binds to the cell membrane.
what is the second step of phagocytosis?
the phagocyte uses its cytoskeleton to push its cell membrane around the bacterium, creating a large vesicle, the phagosome.
what is the third step of phagocytosis?
the phagosome containing the bacterium separates from the cell membranes and moves into the cytoplasm.
what is the 4th step of phagocytosis?
the phagosome fuses with lysosomes containing digestive enzymes.
what is the 5th step of phagocytosis?
the bacterium is killed and digested with the vesicle.
what are types of epithelial transport?
paracellular transport
transcellular transport
paracellular transport
occurs through junctions between adjacent cells
transcellular transport
occurs through cells themselves
transcytosis with vesicular transport
separating positive charges from negative charges requires____.
energy
what creates the membrane potential?
bc separated charges have the “potential” to do work, this potential is known as the membrane potential.
cell and solution are _____ and ______ at equilibrium
electrically and chemically
what cases a change in charge of membrane potential?
the Na+K+ pump sets the concentration gradients which then also changes charges inside and outside the cell. all you need is one cation to leave the cell to set the gradient.
what prevents free movement of ions between the intracellular and extracellular compartments?
the cell membrane. It acts as an insulator.
is the membrane positive or negative inside and outside the cell?
the inside of the cell is negative and the outside of the cell is positive. but its only along the membrane everywhere else is pretty neutral.
are there more K+ leak channels or Na+ leak channels?
There are more K+ leak channels.
What if there were no K+Na+ pump?
the ions would leak until they were equal on both sides.
what is K+ permeability?
50-75
what is K+ ECF concentration?
5mM
what is K+ ICF concentration?
125mM
what is Na+ permeability?
1
what is Na+ ECF concentration?
125mM
what is Na+ ICF concentration?
10mM
what is anion permeability?
0
what is anion ECF concentration?
0mM
what is Anion ICF concentration?
65mM
why is K+ so permeable?
because of all of it’s leak channels
the _____ gradient drives K+ out of the cell.
concentration
the ____gradient moves K+ back into the cell
electrical
What is the reversal potential/electrochemical gradient for K+?
-90mV
it occurs for potassium.
What causes the electrical gradient?
as the concentration gradient pushes K+ out of the cell the outside of the cell becomes more positive relative to the inside, especially since the anions (-) is impermeable so that makes it even more neg inside.
So what happens when you have a concentration and electrical gradient?
they push in opposite directions and that’s how you get the gradient at -90mV
does the electrical force exactly oppose the chemical force?
yes!
explain the electrochemical gradient?
initially the concentration gradient is greater but the move towards more towards +90mV outside (more positive), the elect gradient kicks in and they will be equal and opposite .
Na+ ____ gradient tends to drive Na+ INTO the cell.
concentration
the electrical gradient tends to move Na+___ of the cell.
out
what is the electrochemical gradient for Na+?
+60mV
which equation is used to determine equilibrium potentials?
the Nernst equation
What is the resting membrane potential potential?
-70mV
What is the resting membrane potential potential?
-70mV
why is membrane potential -70mV
K+ is the main mediator of the membrane potential because of all of the K+ leak channels so the membrane so that is why the potential is closer to that of K+. the little bit of Na+ that leaks in offsets the -90mV to -70mV
why is membrane potential -70mV
K+ is the main mediator of the membrane potential because of all of the K+ leak channels so the membrane so that is why the potential is closer to that of K+. the little bit of Na+ that leaks in offsets the -90mV to -70mV
