what types of membrane proteins are in the lipid bilayer of the cell membrane?
1) carrier proteins
how do carrier proteins work?
operate in cycles
bind solutes (i.e. their substrates), undergo conformational changes that convey the solutes across the membrane, & return to the initial conformation
each has a characteristic Km & Vmax
how do channels work, broadly?
allow for higher rates of movement across membranes than do carrier proteins
do not tightly bind solutes or operate in cycles; provide a TM pore through which specific solutes can diffuse down their electrochemical gradients
what do carrier proteins establish across cell membrane? what is return?
thus ionic composition of cytoplasm of any cell is very diff from that of surrounding extracellular space
what do ion gradients represent? what happens within/outside of cell?
represent a form of potential energy
free energy of a system will decrease as ions move from region of high concentration to low concentration
how is transmembrane voltage/potential generated?
ions moving through the membrane produce a transmembrane voltage/potential
opening & closing channels that are selective for particular ions allows cells to regulate the voltage across the cell membrane
high rates of charge transfer can produce dramatic voltage fluctuations
what are the terms, their symbol, unit for ions moving through membranes?
what is the membrane potential?
the inside voltage relative to the outside
typically = -70 mV
what are typical ion concentrations of K+, Na+, Ca2+, and Cl- inside/outside the cell?
which channels provide predominant membrane conductance?
explain the relationship between the concentration gradient and electrostatic force for K+ channel?
1) concentration gradient wants K+ to leave the cell b/c there is 150 inside and 4 mM outside, so K+ goes out per concentration gradient. The electrostatic force does not yet act bc there is no voltage gradient
2) As K+ continues to leave the cell, generate a negative force across the voltage gradient. Concentration gradient still pulling K+ out. Electrochemical gradient slightly wants it to stay in but not that strongly
3) Now if get to -91 mV gradient. Electrostatic gradient really kicks in and wants K+ ions to stay in the cell, big time! No net movement of K+ in/out of the cell - do have movement in and out but not net movement
Get to Vm, the point where electrostatic attraction and concentration gradient are equal
what is the equilibrium potential?
the value of Vm where the concentration gradient and electrostatic forace are balanced
what is Veq for Na+, K+, Ca2+, and Cl-?
Na+: +67 mV
K+: -91 mV
Ca2+: +125 mV
Cl-: -78 mV
what is "outward current"?
what is effect on membrane?
the movement cations out of the cell
what is inward current?
what is effect on membrane?
movement of cations into the cell
depolarizes the membrane
what is current?
what is it determined by?
rate of charge transfer from 1 point to another
large current means that many charges (ions) are moving through the membrane per unit time
1) electrochemical gradient for this ion
2) ease w/ which this ion can pass through the membrane
what is the driving force of an ion?
driving force = |Vm - Veq|
changes in response to variatiosn in membrane potential
what is conductance?
the ability of a material to carry a current
expressed in siemens
what is resistance?
inverse of conductance (which is ability of a material to carry a current)
unit = ohm
"how good a barrier a medium presents to ions/charges"
how is the resistance of biological membranes?
what is Ohm's law?
what is its slope?
I = g*V
if there are fewer ion channels open in a membrane, will the membrane potential change be great or small in response to application of a current?