Membranes Flashcards
Are sodium ions extracellular or intracellular?
Extracellular.
Are potassium ions extracellular or intracellular?
Intracellular
Can ions move across capillaires?
Yes.
What molecules can cross the cell membrane?
Oxygen and carbon dioxide.
What function of the cell membrane helps with the transmission of nerve impulses?
The fact that the permeability can increase/decrease at different times.
Membranes are dynamic. What does this mean?
It means they are continually being formed and maintained or dismantled and metabolized according to the needs of the cell.
What is the lipid bi-layer composed of?
Thin double layers of sheets of lipids.
What makes membranes flexible?
Fatty acids which behave like oil.
What can membrane carbs attach to and what are they called when they attach?
Lipids- glycolipid
Protein- glycoprotein.
What are intergral proteins?
Proteins which span the hydrophobic core of the lipid-bilayer/whole membrane.
What are peripheral proetins?
Only span one side of the cell membrane.
Name five functions of membrane proteins.
- Receptors
- Transport (transporter and channel proteins).
- Enzymes
- Maintenance of cell structure (anchorage).
- Commuinication.
Are receptors integral or peripheral to the membrane?
Integral.
What do receptors allow?
Communication of an extracellular chemical signal to the intracellular space to create a response.
Are transporters integral or peripheral?
Integral.
What do transporters allow?
Movement of ions or molecules across the membrane.
Name the two form of transporters.
Channels and transporters.
What do channel proteins do?
Create a pore in which molecules, like water and ions, can flow.
If a channel protein is open, which molecules can pass through?
Water.
If a channel is gated, which molecules can pass through?
Ions.
When are transporters open to ECF/ICF?
Open to ECF, then ICF, but never at the same time.
Which larger molecules can transporters tranposrt?
Glucose.
What do enzymes do?
Catalyse chemical reactions on the cell membrane.
Which side of the membrane can enzyme reactions take place?
Both! External/intrernal.
What do structural proteins do?
Anchor the cell membrane to the intracellular skeleton, extracellular matrix and/or other cells.
What do glycoproteins act as?
Markers that tell the immune system whether a cell is one of our own or foeign.
Other types of protein can carry extracellular messages via hormones or drugs to the intracellular environment.
What do they convert extracellular signals into?
Intracellular response.
What is the protein content of Myelin?
18%.
What is the protein content of the plasma memrbane?
50%.
What is the protein content of other membranes involved in energy transduction such as the inner membranes of mitochondria?
75%.
Define electrochemical gradient.
The difference in charge and chemical concentration across a membrane
What do electrochemical gradients drive?
Mercedes :)
jk its the direction of passive movement
What is required if we want to move something against the electrchemical gradient?
Energy (it’s active transport).
Name the four mechanisms of movement across membranes.
- Diffusion
- Active transport
- Osmosis
- Filtration
Describe the different types of diffusion.
Passive diffusion goes through the lipid bilayer.
Facilitated diffusion moves through either protein channels or protein transporters.
Which movements occur across the membrane (e.g. between ICF & ECF)?
Diffusion, active transport and osmosis.
Which movement occurs between plasma and ISF?
Filtration.
What are the two mechanisms for moving macromolecules across membranes without disrupting them.
Endocytosis and Exocytosis.
What are the two mechanisms for moving macromolecules across membranes without disrupting them.
Endocytosis and Exocytosis.D
Describe the process of endocytosis.
There is invagination of the cell membrane to form a vesicle which eventually disintegrates on the cytoplasmic (inside) surface of the membrane, releasing contents which then migrate within the cell to their destination.
Define the process of exocytosis.
Exocytosis involves the reverse process. Many proteins manufactured in cells are released from those cells by the process of exocytosis.
Define diffusion.
Molecules go from regions of a high concentration to regions of a low concentration. In the body, diffusion occurs from one compartment to another providing the barrier between the two is permeable.
If molecules want to pass passively, what factors must they have?
Must be-
1. Uncharged
2. Small
3. Lipophilic (hydrophilic).
Define passive diffusion.
Substance moves directly through the lipid bilayer.
Define facilitated diffusion.
Substance requires assistance from membrane proteins to cross the lipid bilayer.
Name a molecule which may undergo passive diffusion.
Oxygen, carbon dioxide.
Name a molecule which may undergo facilitated diffusion.
Glucose.
Is passive diffusion a fast/slow process?
Fast.
What molecules may require facilitated diffusion?
Charged ions, larger molecules like glucose.
Describe voltage gated ion channels.
They open/close in response to changes in electrical potential across the membrane.
Where are voltage gated ion channels found?
Muscle and nerve cells.
Describe ligand gated ion channels.
They open/close in response to a chemical binds to a receptor binding site on the channel protein.
Name two chemicals which may bind and cause the opening of a ligand gated channel.
Hormones and neurotransmitters.
What causes ion channels to open/close?
A change in confromation.
What does the net direction of movement depend on?
The dominant force.
What is membrane potential?
The difference in electric potential between the interior and the exterior of a biological cell.
When is electrochemical equilibrium met?
When the electrical and chemical gradients are in balance.
Is the inside of a cell usually positively or negatively charged compared to the outside of the cell?
Negatively.
If a molecule is too big to be transported across a membrane, how can they be transported across?
Will use carrier-mediated transport proteins or “transporters”.
If electrochemical gradient favours direction of movement, movement occurs by diffusion and no energy input is required.
What process is required?
Facilitated diffusion.
If the electrochemical gradient opposes movement then energy in the form of ATP is required to move the molecule against this gradient.
What process is required?
Active transport.
Define active transport.
Molecules are transported against their electrochemical gradient.
Cells want to maintain electrochemical gradients.
How do they do this in regards to sodium and potassium pumps?
[Na+] is higher outside the cell, and [K+] concentration higher inside and the cell likes to keep it this way. Na+/K+ ATPase occurs in ALL cells and helps maintain this difference by continually pumping out 3 Na+ ions and pumping in 2 K+ ions (both against concentration gradients) for each molecule of ATP hydrolysed.
How much of resting energy of the body is used by Na+/K+ ATPase?
40%.
Describe the difference between osmosis and diffusion.
Osmosis is the net movement of H2O from regions of high H2O concentration to regions of low H2O concentration.
Diffusion is the net movement of solute from regions of high solute concentration to regions of low solute concentration.
Osmosis occurs where there is a membrane…
that is only permeable to water.
In what process is there a change in volume?
Osmosis.
If we have diffusion, do we have osmosis too? Why?
Yes- water and solute move, in opposite directions.
If we have osmosis, do we have diffusion too? Why?
Not necessarily- if the membrane is only permeable to water, then water moves but the solute does not (so no diffusion).
How many moles of water will be displaced if 1 mole of NaCl is added to 1L H2O?
2 moles/litre.
This is because you have 6.02 x 1023 molecules= 1 mole for the sodium and 6.02 x 1023 molecules=1 mole for the chlorine hence the 2 mole/litre.
(6.02 x 1023 molecules of NaCl in solution
Will give
6.02 x 1023 molecules of Na+
and
6.02 x 1023 molecules of Cl-)
Osmolarity measures the concentration of?
Biological solutions.
What unit is osmolarity measured in? And what, as biologists, do we measure it in?
Osmoles but milliosmoles, because biological solutions are so weak.
What is the osmolarity of human plasma?
285 mOsmol/l
Is rounded up to 300mOsmol/l
In the ECF, which molecules act as non-penetrating solutes?
Sodium and chlorine.
In the ICF, which molecule acts as a non-penetrating solute?
Potassium.
What does osmolarity describe?
Total number of particles in solution
What does tonicity describe?
The number of non-penetrating particles in solution
An isosmotic solution has…?
the same number of solute particles as normal ECF.
Solutions with fewer total solute particles are …?
Hypo-osmotic.
Solutions with greater number of total solute particles are…?
Hyper-osmotic.
An isotonic solution has…?
The same number of non-penetrating solute particles as normal ECF (plasma).
Solutions with fewer non-penetrating solute particles are?
hypotonic
Solutions with greater number of non-penetrating solute particles
hypertonic.
What determines osmolarity?
Penetrating PLUS non-penetrating particles
Give an example of a non-penetrating particles.
Ions.
Give an example of a penetrating particle.
Urea
Why is the osmolarity of our ICF and ECF the same?
Because there are no barriers to the movement of water.
Water moves to ensure the number of molecules are the same on both sides of the membrane.
Most of the 285 mosmol/litre can be attributed to which molecules?
Sodium and chlorine.
What do plasma samples come back with information on?
The osmolality of the blood sample.
What can the composition of osmolality be used to tell us?
The composition of osmolarity can be used to predict the tonicity of the cells as well as cellular volume.
What do cells in hypotonic solutions do? Why?
Swell.
Water enters down an chemical gradient.
What do cells in hypertonic solutions do? Why?
Shrink.
Water leaves down an chemical gradient.
What is the condition of Intravascular haemolysis and what could be the consequences?
Red blood cells burst. Could cause death.
What do you never transfuse a patient with?
Pure water.
If you put a normal cell in a beaker of water, what will happen? Why?
It will swell up and burst.
Although the penetrative molecules will move to create equilibrium but the non-penetrative molecules will cause water to enter the cell.
What would happen if you put a red blood cell in a beaker of water? Why?
It would swell and burst due to water moving in by osmosis (due to presence of non-penetrating ions in the ICF).
Are membrane carbohydrates extracellular, intracellular or both?
Extracellular
Which type of cell’s membrane has a low protein content?
Myelin (18%)
What is the major component of myelin?
Lipid
Which cells have the most protein?
Cells involved w energy transduction like the inner membrane of the mitochondria (75%)
Why do gases easily pass through the cell membrane?
They are small and uncharged.
Name two gases which are lipophilic.
Oxygen and nitrogen.
Where are voltage gated ion channels often found?
In nerve and muscle cells.
Define electrogenic pump.
The net movement of positive charge out of the cell.
