Membrane Permeability Flashcards
What properties/types of molecules are more permeable to pass through membranes?
Small, uncharged, polar. Hydrophoic
Why can H2O pass through membranes often really easily?
Even though it is hydrophilic, because it is so small and polar, its small enough to pass through.
List some molecules and why they cant pass through the membrane that easily?
Ions- K+, Na+, Cl-. As they have a full charge. Large polar uncharged molecules eg glucose- because theyre so big.
What do transport processes allow to happen? What is their role?
Maintaining pH, ionic composition maintenance, regulate cell volume, generate ionic gradients, control conc of metabolic fuels
Thermodynamically, what is the difference between active and passive transport?
Active: requires energy (+ΔG) Passive: gives off energy (-ΔG)
List some basic ways a molecule can be transported through a membrane
Via a gated pore, ligand gated ion channels, voltage gated ion channels, gap junctions.
Describe what happens with a gated pore.
The transporter protein undergoes a conformational change to move the substrate from one side of membrane to the other
Describe process that happens with ligand gated ion channels
Ligand (eg transmitter or hormone) binds meaning the channel can then open. Eg nicotinic ACh receptor
Describe process of how a voltage gated ion channel works
Membrane is usually -ve on inside and +ve on outside, if this changes causes ion channel to open
What are gap junctions, how do they work?
Aggregate of intercellular channels, directly connects the cytoplasm of two cells. They allow the movement of various molecules between them
Whether the movement across a membrane needs energy depends on….
- concentration ratio (if you move against, needs energy)
- membrane potential (if you move an ion to an area of the same charge, needs energy)
List the three types of ‘porters’ and what they do
Uniport, symport, antiport. Uni- transports 1 thing, Sym- moves 2 at the same time from one side to the other, Anti- moves 1 from one side and 1 from another (opposites)
When are transporters referred to as pumps?
When they are primary ATP transporters. (Ie ATP binds to transporter and hydrolysis occurs directly on it)
What does active transport enable you to do?
Overcome unfavourable chemical or electrical gradients. They must be coupled to a thermodynamically favourable reaction.
Which transporters are involved in the transport of calcium?
PMCA, SERCA, NCX, mitochondrial Ca2+ uniports
For Na, K, Cl, Ca, state whether their conc is higher inside or outside the cell.
Na+ higher outside the cell. K+ higher inside the cell. Cl- higher outside. Ca2+ higher outside cell.
What does PMCA stand for?
Plasma membrane Ca2+ ATPase
What does PMCA do?
Pumps (1°) Ca2+ from inside cell to outside. Needs Mg2+, ATP hydrolysed directly on it. Has high affinity for Ca2+ but low capacity.
What does SERCA stand for?
Sarco/endoplasmic reticulum Ca2+ ATPase
What does SERCA do?
Pumps (1°) i Ca2+ into cell and H+ out. Has high affinity (stores residual Ca2+) but low capacity.
What do mitochondrial Ca2+ uniports do?
Operates at high [Ca2+] to buffer Ca2+ levels. NOT ACTIVE TRANSPORT!!! Moves Ca2+ into mitochondria
What does NCX stand for?
sodium (Na), Calcium eXchanger
What does NCX do?
Antiporter, transports 2Ca out of the cell and transports 3Na in. Its a 2° transporter as ATP is hydrolysed elsewhere. Has low affinity, high capacity.
When can NCX reverse? What results?
If the cell becomes depolarised, the 3Na+ cant be pumped to an area of +ve TF 2Ca+ are brought into the cell and 3Na+ are transported out. High levels of [Ca] are toxic to cells though
