Control of Cells Flashcards
(69 cards)
What are the components that make up a cell membrane?
Lipids = 42% weight Proteins = 55% weight Carbohydrates = 3% weight
What are the three categories of ion channels?
Carries, pumps and gated channels
What is the role of carriers?
Facilitate movement using passive diffusion
Binds ions/solutes causing a conformational change
Requires a concentration gradient
What is the role of pumps?
Use active transport to move ions against their concentration gradient
What is the role of gated channels?
Cylinder protein with a gated pore so not always open critical for physiology
What are the two driving forces for the movement of ions?
Potential (charge) and chemical (concentration)
What is the turnover of active transport?
<100/second - not very fast as molecules move down their concentration gradient and ATP has to be hydrolysed first so phosphate must be present
Where are sodium potassium pumps not found?
Red blood cells in dogs
What is the structure of sodium potassium atpase?
4 subunits - 2 alpha and 2 beta
What can block sodium potassium atpase?
Nitric oxide
What is meant by a secondary active transporter?
A carrier which relies on the activity of an ATPase in order to work eg sodium potassium atpase works to keep IC low
What is the turnover of a carrier?
10^2 to 10^3 molecules per second
What are the three classifications of carrier?
Uniporter, symporter and antiporter
What is the turnover of gates ion channels?
10^6 to 10^8 ions per second
Who developed the patch clamp technique?
Nehr and Sakman
What is the patch clamp technique used for?
To directly see or measure ion channels opening and closing in a cell
How is a patch clamp test carried out?
A glass pipette is used which contains a silver electrode and a salt solution of a known concentration
Another electrode is in an experimental bath
The glass pipette touches the back of the cell - when sucked it seals the membrane (cell attached configuration)
This allows the function of a single ion channel to be measured
If the membrane is broken the current through all channels can be measured (whole cell configuration)
What is the equation used to work out total current?
I = N x Po x g x (Vm-Ei) I = current N = no. of channels Po = open probability g = single channel conductance Vm = membrane potential Ei = Equilibrium potential of ion
How can ion channels be regulated?
Number of channels at membrane The open probability of the channel - affected by phosphoryl, calcium and g proteins etc The potential (Vm - Ei)
What is the general structure of a voltage gated potassium channel?
6 transmembrane spanning domains in each of the 4 subunits
What is the general structure of a kir protein?
2 transmembrane spanning domains in each of the 4 subunits
What is the general structure of a voltage gated sodium channel?
24 transmembrane spanning domains in 1 subunit
beta 1 and 2 regulate the ion channel
What is KcsA?
A bacterial K+ channel homologous to the kir mammalian family
How was Vm measured before the patch clamp technique was developed?
A glass electrode is filled with solution (1m KCl) and a silver electrode is also used with respect to zero Vm
The diameter of the tip used is much smaller than that used in patch clamping (1x 10^-6) and is very sharp
This measures Vm but does not tell us what causes it
