CBG 30 Flashcards
Inward current?
becomes more +: more + in or - ions out
what is outward current?
less positive: more - in or + ions out
What is the inside membrane resting potential?
-70mV
what are the equilibrium potentials of NA+,K+ and Cl-?
+40
- 100
- 60
what is reversal potential teh same as?
equilibrium potential
define depolarisation,repolarisation and hyperpolarisation?
Depolarisation-the membrane potential becomes less negative, occurs when sodium channels open and Na+ ions enter the cell.
reploarisation-return of membrane towards resting potential of cell. Na channels close .In addition, additional potassium channels open allowing K+ ions to exit the cell.
hyperpolarisation- overshoot and membrane become more -ve.The additional K channels stay open even when the membrane potential reaches the resting level. So, the potential goes even more negative than resting
what is the rearranged Nernst equation? (logged)
E=0.058/z log [X]1/[X}2
why does internal calcium levels have to be kept low?
interfer with signalling otherwise
what is electric charge (Q) measured in?
C coulombs
What is voltage and what is it measured in?
electromotive force EMV /electric potential between 2 points expressed in V ie resting potential
What does ohms law state?
current is proportional to the voltage and inversely proportional to the resistance V=IR
what is the flow of charge ?what direction is flow?
Current (I) measured in amperes A. flow is direction positive charge moves
what is resistence, what is it measured in and what is a biological example?
property that hinders flow of current and measured in ohms.
plasma membrane with ion channels closed (high resistance) and when open (low resistance)
what is the difference between capacitance and conductance?
conductance (G) is the recipricol of resistence and is measured in siemens (s)
capacitance is the property of a non conductor to store electric charge. measured in farads. ie plasma membrane stores electricsal charge because of all the charged proteins and potential difference between outside and inside.
I
current
ohms
measurement of resistance
G
conductance measured in siemens S
S
measure of conductance
C
capacitance (farads)
farads
measurement of capacitance
V=IR
ohms law
V or E
voltage measured in V
Q
electric charge measured in C coulombs
farads
measurement of capacitance
usually ratio of Na/K+ pumped in /out?
3 Na+ out
2 K+ in
why does the membrane have a capacitance?
lipid core is an insulator and it can store charge.
what i the ion channel in the circuit analogy?
a resistor
what does the membranes ionic conductance depend on?
presence of open ion channels
T or F there is lots of membrane negativity in the neighbourhood of the membrane?
false. there is mostly electrical neutrality in the neighborhood of the membrane.
why is there mostly electrical neutrality in membrane neighborhood?
cell membrane separates charges with cations and anions forming a diffuse layer on opposite sides of the mebrane. charges are held in a narrow thin region due to electrostatic interactions but the bulk solution on either membrane side is electronically neutral.
uniporter
transports single ion in one direction
symporter
transports 2 ions in the same directioj
antiporter
transports 2 ions in opposite directions
what is an example of an antiporter?
Na+/ca2+ which uses force of Na+ flowing in cell to transport Cl AGAINST conc gradient OUT of the cell (ca interferes with signalling)
what are said to be rheogenic and why?
ionic pumps that produce a net charge.
they produce a transmembrane electric current
what is said to be electrogenic?
the pump if its current produces a large effcect on the voltage across the membrane
cardiac glycoside ouabain?
a drug that blocks NA+/K+ ATPase by competing for K+ binding site. (inhibits active transport)
what blocks NA+/K+ ATPase by competing for K+ binding site?
cardiac glycoside oubain
what does the ATPase in the na/k pump have wrt aa types?
501 LYSINE
369 ASPARTATE
where does the enmergy for active transport come from?
hyrolysis of ATP by ATPases present in the membrane
what is the Na+/k+ radient the pump has to work against?
10:1 gradient
what does cyanide do?
prevents production of ATP–> brings active transport to a halt
does NA+/K+ ATPase transport Li+?
no,active transport systems exhibit a high degree of selectivity (despite Li+ having similar characteristics of Na+)
Briefly describe the basic action of the 3Na+/2K+ ATPase pump?
1) transporter binds 3Na+ from cytosol
2) phosphorylation by ATP favours conformational change allowing Na+ to be released
3) Na+ is released and K+ binds
4) dephosphorylation favours original conformation
5) K+ is released to cytosol and cycle can repeat
