ICPP - Membrane Permeability Flashcards
What is a semi permeable membrane?
A layer through which only allowed substances can pass.
Why do human eyes sometimes appear red in photos?
The pupil normally absorbs light, but sometimes it will reflect back red light.
Which of these molecules can pass through the membrane easily? Hydrophobic molecules, small uncharged polar molecules, large uncharged polar molecules, ions.
Hydrophobic and small uncharged polar molecules.
H2O has a very high permeability coefficient. What does this mean in regards to the amount of time it takes for a molecule of H2O to pass through the membrane?
It does not take long.
Which two factors does the rate of passive transport depend on?
Permeability and concentration gradient.
True or false - the rate of passive transport decreases linearly with increasing concentration gradient.
False - it increases.
What are the roles of transport processes?
Maintenance of ionic composition, pH and volume of cell; expulsion of waste products; concentration of metabolic fuels and generation of ion gradients (for action potential).
Why are the reciprocating and rotating models of membrane transport proteins generally regarded as wrong?
They require a huge amount of energy and are therefore thermodynamically unlikely.
Which sort of ion channel is a nicotinic acetylcholine receptor?
Ligand-gated ion channel (ACh binds to it)
In an ATP sensitive K+ channel, ATP binds to the channel which causes it to close. What sort of ion channel is this?
Ligand-gated ion channel
Which takes longer - simple or facilitated diffusion of glucose?
Simple
If delta G is positive, is the transport active or passive?
Active
What two things decide whether transport is active or passive?
Concentration ratio and membrane potential.
What is active transport?
The transport of ions or molecules against an unfavourable concentration and/or electrical gradient, which requires energy from ATP.
Give a disadvantage of a carrier compared to a channel.
Carriers are slower and less efficient.
One of these ions (Na+, K+, Cl-, Ca2+) is the odd one out and has a higher concentration inside the cell than outside. Which one?
K+
What is the conc. of Na+ inside vs outside the cell?
Inside - 12 mM
Outside - ~145 mM
What is the conc. of Cl- inside vs outside the cell?
Inside - 4.2 mM
Outside - 123 mM
What is the conc. of Ca2+ inside vs outside the cell?
Inside - 10^-7 M
Outside - 1 to 1.5 mM
(Much higher outside).
What is the conc. of K+ inside vs outside the cell?
Inside - 155 mM
Outside - 4mM
What does Ca2+ ATPase (PMCA) do?
It transports Ca2+ ions to the outside of the membrane, which uses ATP. It is a PRIMARY ACTIVE TRANSPORTER.
What does ATP synthase do?
It forms ATP from ADP as H+ ions pass through it. It is used in oxidative phosphorylation.
What is uni-transport?
One molecule being transported through a membrane at a time.
What is co-transport?
When more than one type of ion or molecule is transported through the membrane transporter per reaction cycle.
What is the difference between symport and antiport?
They are both types of co-transport - symport is two molecules travelling in same direction together, antiport is two molecules travelling in different directions at same time.
What does Na+K+-ATPase (sodium pump) do?
Pumps 3 Na+ ions out for every 2K+ ions in to cell, which is very important for action potential. Found in membrane, uses ATP (active transport), 25% of basal metabolic rate used for this pump.
How many subunits does a sodium pump have?
Two - alpha contains binding sites and beta contains glycoproteins and directs pump to cell surface.
Why are sodium pumps important in relation to action potentials?
They create a high intracellular K+ which maintains resting membrane potential.
What does Ca2+Mg2+ATPase transport? What sort of transport is it?
It transports Ca2+ out of the cell using active transport. This is “uniport”. It has a HIGH affinity, but LOW capacity.
What does Na+Ca2+ exchanger transport? What sort of transport is it?
Inward flow of 3 Na+ down conc gradient drives outward flow of one Ca2+ up gradient. This is antiport, and has LOW affinity but HIGH capacity.
What is the function of Na+H+ exchange?
Inward flow of Na+ down its concentration gradient leads to cell alkalinisaion by removing H+ (antiport).
Where does Na+glucose co-transport occur? What happens during it?
Small intestine and kidney, entry of 2 Na+ provides energy for entry of one glucose molecule against conc. gradient.
Which disease occurs due to the CFTR protein not opening? Why?
Cystic fibrosis - Cl- ions cannot flow through so mucus is thick and sticky.
Which diseases occurs when the CFTR protein stays open too long?
Cholera - flow of Cl- ions lowers water potential of lumen of intestine so diarrhoea occurs.
