Core Physiology Flashcards
Remember that the cell membrane has extracellular and intracellular compartments. Its made of carbs, lipids and proteins. What are the proportions of these 3 materials in the membrane?
Carbs = 3%
Proteins 55%
Lipids = 42%
What is the typical levels of sodium inside and out of the cell? In terms of higher and lower. And which enzyme ensures this balance?
Inside the cell sodium levels are low usually . This is the intracellular
Usually outside the cell levels are higher
This is maintained by the sodium potassium ATPase
Is potassium usually higher or lower inside of the cell (in the intracellular)?
It is usually higher inside than outside of the cell
Is calcium usually in higher levels inside or outside of the cell?
Calcium is usually in a higher amount outside of the cell
This allows for their movement in during depolarisation
Is potassium carbonate hco3- higher inside or outside of the cell?
Trick question. It is in relatively the same amounts inside and outside of the cell
Chloride levels inside of the cell?
These are typically low inside the cell of 6mM
Outside is typically higher
Is there a lot of phosphates inside of the cell? And why?
Yes!
This is because they form ATP
Where can more proteins be found. Inside the cell (intracellular fluid) or in the bloods plasma (extracellular fluid)?
More can be found in the extracellular (in the plasma)
What is the process of moving large molecules in and out of cells called?
Endocytosis
What is the typical turnover rate of pumps?
Such as the sodium potassium pump
This is usually less. Than 100 ions into the cell per second
What is secondary active movement
This is when an ion relies on passive diffusion
However this passive diffusion has been enabled by a pump for example (which uses ATP and active transport) to set up the diffusion gradient
For instance an ion may passively diffuse out of a cell, but it may require an ATP pump to firstly bring it into the cell.
ATPase structures and characteristics? How many ions does it bring in and out? What is the pump described as electrogenic
It has a ubiquitous structure - found everywhere in the body
It has a tetramer structure - 2 alpha and beta sub units
It brings in 3 sodium and moves out two potassium
The pump is electrogenic because it moves ions
What is facilitated diffusion?
Passive diffusion is when a ion passes through a channel down its concentration gradient
Facilitated diffusion is also when an ion moves down its concentration gradient through a channel. However in doing so it binds to an ion in the plasma membrane and causes it to undergo a conformational change
An example is a glucose co transporter
What is the turn over rate of facilitated proteins? And what was the rate for a pump?
The turnover rate is 10 ^2 to 10^3 ions per second.
This is because these proteins dont rely on ATP
Remember pumps turnover less than 100 ions per second. Thus this is LESS than facilitated proteins
What is meant when said that facilitated proteins have a cut off point?
They have a limit as to how many proteins they can transport
This is because the rate of transport is limited (to 10^2 or 10^3 ions per second) and the NUMBER of facilitated protein channels is limited
What are the three classes of facilitated proteins?
Uniporters
Symporters = these are involved in co transport of ions but these ions move in the same direction
Antiporters = move more than one ion but these ions move in OPPOSITE directions
What are conductive and non conduction ion channels?
No conductive channels dont rely on a flow of ions or a current (so they aren’t voltage gated basically, they’re ligand gated)
Conductive ion channels rely on ion flow and a current.
Ion channel turn over rate? And how does this compare to the turn over rate of pumps and facilitated transporters?
Ion channels have the highest turnover rate!!
10^6 to 10 ^8 ions per second.
Facilitated protein channels have the SECOND highest turnover rate of 10^2 - 10^3
Pumps are ATP DEPENDENT and thus have the lowest turnover rate of less than 100 ions per second
What does the patch clamp technique tell us?
It allows us to directly measure the function of one channel or lots of channels in the plasma membrane of a cell
How do you do a patch clamp?
Stages up until the cell attached configuration:
Seal a patch pipette onto a cells membrane surface but sucking on the back of the pipette to get the pipette to SEAL to the membrane
This diameter is 1 micron
This is the cell attachedconfiguration
You can measure the current across the cell membrane at this point to find the flow through a SINGLE channel. Do this using a bath in the pipette which has no current.
How do you get the whole cell configuration in a patch clamp experiment?
Remember the attached cell configuration was achieved but sucking up part of the cells membrane and then measuring the current.
You remove the whole membrane of the cell by sucking it up with a pipette
This is the whole cell configuration
You can now measure current levels across the whole cell
Why do we clamp the membrane potential of a cell?
This allows us to keep the membrane potential of a cell at a specific number so we can measure the change in membrane ion potential currents.
How can we use a patch clamp test to study mutated ion channels?
Do the patch clamp technique to whole cell and attached configurations. See if there are changes in ion flow in comparison the cells which aren’t mutated.
The equation for current across ion channels is:
I = N x Po x g (vmiEi)
What does each part stand for?
I = total current carried by a population of channels
N = number of channels
Po = open probability = this will vary from zero to one . One being channel is open all them time. This is affected by current
G = single channel conductance = number of ions travelling through a pore. This is a constant
Vm = membrane potential
Ei = eqm potential.
How does current affect open probability? Po?
The lower the open probability, the smaller the current
What may affect the number of channels in a membrane?
Membrane shuffling.
How many sub units do potassium, sodium, Ach and CFTR cl- channels have
Potassium channels have 6 sub units
Sodium has 24 - in groups of 4
Ach has 4 sub units
CFTR CL- channels have 2 lots of 6 transmembrane domains
Potassium channels? Structure?
Have 4 sub units
Has a centre and a crystal structure
Examples of electrogenic transporters?
Na / K ATPase
Na / glucose co transporter
Potassium channel
