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-
