Session 2 Flashcards
What can pass through membranes?
Hydrophobic molecules
Small, uncharged polar molecules
What cannot pass through membranes?
Large, uncharged polar molecules
Ions
What passive diffusion?
It is dependent on permeability and concentration gradient.
The rate of passive transport increases linearly with increasing concentration gradient.
What is facilitated diffusion?
Has specific proteins in the bilayer that allow molecules through.
What are the two carrier molecules in models for facilitated diffusion?
Carrier molecules, usually gated pores (use ping pong transport)
Protein channels
What is active transport?
Allows the transport of ions or molecules against unfavourable concentrations and/or electrical gradients. Uses energy from the hydrolysis of ATP.
How do voltage gated ion channels work?
There is a voltage sensor, when the optimal voltage is detected, the channel opens to allow ions through.
How do ligand gated ion channels work?
A molecule will bind (the ligand) which causes the channel to open and let the ion through.
What are Co-Transporters?
A membrane transporter than can move more than one molecule per reaction cycle.
What are the 3 types of transporters? (Classified by how many molecules they can carry)
Uniport - Single molecule. One direction
Symport - Two molecules. Same direction.
Antiport - Two molecules. Opposing direction.
How does the Na+ Glucose co transport system work?
Extra point - Where is it in the body?
Entry of Na+ provides energy for the entry of Glucose against the gradient. (Symport)
Extra Point - Small intestine and Kidney.
What are the 2 subunits of Na+/K+ ATPase?
Alpha - binding sites for K+, Na+, Ouabain and ATP
Beta - Glycoprotein for directing the pump to the surface.
Does Na+/K+ ATPase use active or passive transport?
Uses ATP to pump ions so active transport.
What molecule inhibits the Na+/K+ ATPase?
Ouabain binding to the alpha subunit.
What type of co transport does the Na+/K+ ATPase pump use?
Antiport - 2K+ in ans 3Na+ out.
What is the importance of Na+/K+ ATPase?
It forma Na+/K+ gradients which are necessary for other things such as electrical excitability.
Also drives secondary active transport which has many roles eg control of pH, cell volume, Ca2+ concentration and nutrient uptake.
What is the main role of K+ channels?
They allow K+ (High concentration from Na pump) to diffuse down the concentration gradient. They are the main cause of membrane potential being -70mV.
What is the main role of Ca2+ ATPase?
Extra point - Does it use active or passive transport?
It controls the resting Ca2+ concentration
Extra point - It uses active transport.
What is the main role of Plasma membrane Ca2+ ATPase?
Extra point - What are the 3 main points about the exchanger?
It removes residual Ca2+ from the cell and bring in H+
Extra point - It is active, an antiport and high high affinity low capacity.
What is the main role of SERCA?
Extra point - What are the 3 main points about the exchanger?
It removes residual Ca2+ into the S/ER in exchange for H+
Extra point - Active, Antiport, high affinity low capacity.
What is the main role of the Na+/Ca2+ exchanger?
Extra point - What are its important properties?
It expels 1Ca2+ from the cell for 3Na+ in using the Na+ gradient set by the Na+/K+ ATPase (removes most of the Ca2+)
Extra point - It uses secondary active transport, Antiport, low affinity high capacity, Electrogenic (Current flows in the direction of the Na+ gradient) and activity is membrane potential dependent.
What happens to the Na+/Ca2+ exchanger in Ischaemia?
Extra point - Why?
The exchanger reverses so Na= in and Ca2+ out (Ca2+ is highly toxic)
Extra point - ATP is depleted so the Na+ pump is inhibited which causes it to accumulate in the cell –> depolarisation.
What are the acid extruders of a cell?
Na+/H+ exchanger.
NBC
What are the base extruders of a cell?
Anion exchanger Cl-/HCO3-
How does the Na+/H+ exchanger work?
It is electroneutral with 1Na+ in and 1H+ out.
Uses the concentration gradient set by Na+/K+ ATPase.
raises intracellular pH
What activates and inhibits the Na+/H+ exchanger?
Activated by growth factors
Inhibited by Amiloride.
How does the NBC exchanger work?
Uses the concentration gradient set by the Na+/K+ ATPase to bring Na+ and HCO3- in and H+/Cl- out. So raises the intracellular pH and regulated cell volume.
How does the Anion exchanger work?
It acidifies the cell by removing base.
Involved in cell volume regulation.
How can ion transport regulate cell volume?
Osmotically active ions are transported in or out of the cell and water follows.
What are the osmotically active ions and organic osmolytes?
Osmotically active ions are Na+ K+ Cl-
Organic osmolytes are amino acids.
What happens to the ions if the cell is swelling?
They move out of the cell so water follows and is lost.
What happens to the ions if the cell is shrinking?
They move into the cell so water follows and is gained.
What is the goal of renal anti hypertensive therapy?
To reduce the reuptake of Na+ so less water is reabsorbed. Therefore reducing blood volume.
How does aquaporin (A protein) work in the kidneys?
Extra point - What causes its inclusion in the membrane?
It allows water to cross the membrane more easily into the cells.
Extra point - Anti diuretic hormone
How do Loop diuretics prevent the movement of water back into the renal cells?
They prevent Na+ reuptake in the thick ascending limb.
How does Amiloride prevent the movement of water back into kidney cells?
It prevents Na+ uptake in the distal convoluted tubule and proximal tubule.
What does Aldosterone do to the Na+ transporters in the kidneys?
Extra point - What can be used to treat high levels of it?
It up regulates the transporters.
Extra point - Spironolactone
What does a faulty CFTR protein cause?
An accumulation of Cl- in a cell so water moves into the cell via osmosis resulting in sticky mucus in the lumen.
What happens to cause Diarrhoea?
CFTR is phosphorylated by Protein Kinase A which causes it to become overly active.
Therefore Cl- is transported into the kumen (excessively)
Water follows by osmosis resulting in symptoms.
