Core Physiology

Question 1

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?

Answer 1

Carbs = 3%
Proteins 55%
Lipids = 42%

Question 2

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?

Answer 2

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

Question 3

Is potassium usually higher or lower inside of the cell (in the intracellular)?

Answer 3

It is usually higher inside than outside of the cell

Question 4

Is calcium usually in higher levels inside or outside of the cell?

Answer 4

Calcium is usually in a higher amount outside of the cell

This allows for their movement in during depolarisation

Question 5

Is potassium carbonate hco3- higher inside or outside of the cell?

Answer 5

Trick question. It is in relatively the same amounts inside and outside of the cell

Question 6

Chloride levels inside of the cell?

Answer 6

These are typically low inside the cell of 6mM

Outside is typically higher

Question 7

Is there a lot of phosphates inside of the cell? And why?

Answer 7

Yes!

This is because they form ATP

Question 8

Where can more proteins be found. Inside the cell (intracellular fluid) or in the bloods plasma (extracellular fluid)?

Answer 8

More can be found in the extracellular (in the plasma)

Question 9

What is the process of moving large molecules in and out of cells called?

Answer 9

Endocytosis

Question 10

What is the typical turnover rate of pumps?

Such as the sodium potassium pump

Answer 10

This is usually less. Than 100 ions into the cell per second

Question 11

What is secondary active movement

Answer 11

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.

Question 12

ATPase structures and characteristics? How many ions does it bring in and out? What is the pump described as electrogenic

Answer 12

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

Question 13

What is facilitated diffusion?

Answer 13

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

Question 14

What is the turn over rate of facilitated proteins? And what was the rate for a pump?

Answer 14

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

Question 15

What is meant when said that facilitated proteins have a cut off point?

Answer 15

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

Question 16

What are the three classes of facilitated proteins?

Answer 16

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

Question 17

What are conductive and non conduction ion channels?

Answer 17

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.

Question 18

Ion channel turn over rate? And how does this compare to the turn over rate of pumps and facilitated transporters?

Answer 18

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

Question 19

What does the patch clamp technique tell us?

Answer 19

It allows us to directly measure the function of one channel or lots of channels in the plasma membrane of a cell

Question 20

How do you do a patch clamp?

Stages up until the cell attached configuration:

Answer 20

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.

Question 21

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.

Answer 21

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

Question 22

Why do we clamp the membrane potential of a cell?

Answer 22

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.

Question 23

How can we use a patch clamp test to study mutated ion channels?

Answer 23

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.

Question 24

The equation for current across ion channels is:

I = N x Po x g (vmiEi)

What does each part stand for?

Answer 24

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.

Question 25

How does current affect open probability? Po?

Answer 25

The lower the open probability, the smaller the current

Question 26

What may affect the number of channels in a membrane?

Answer 26

Membrane shuffling.

Question 27

How many sub units do potassium, sodium, Ach and CFTR cl- channels have

Answer 27

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

Question 28

Potassium channels? Structure?

Answer 28

Have 4 sub units

Has a centre and a crystal structure

Question 29

Examples of electrogenic transporters?

Answer 29

Na / K ATPase
Na / glucose co transporter
Potassium channel