Membranes as Permeability Barriers Flashcards
What is a semi-permeable membrane?
A layer or membrane which only allows specific molecules to pass.
What kind of molecules can pass the lipid bilayer? Give examples.
Hydrophobic molecules BONCO (O2, CO2, N2, Benzene)
Small uncharged polar molecules HUG (H2O, Urea, Glycerol)
What kind of molecules cannot pass the lipid bilayer? Give examples.
Large uncharged polar molecules (Glucose, sucrose)
Ions (H+, Na+, K+, Ca2+ etc…)
What is passive transport? What is it dependent on?
Transport that doesn’t need energy. It is also diffused across the membrane so doesn’t rely on a transporter.
It is dependent on the permeability of the membrane and the concentration gradient.
What are transport processes important for?
Maintenance of: ionic composition intracellular pH Regulation of cell volume Concentration of metabolic fuels and building blocks
How does voltage-gated ion channels work?
Membrane depolarisation brings conformational change which opens the channel.
What’s faster; facilitated diffusion or simple passive diffusion?
Facilitated.
What is active transport?
When energy is needed usually up a concentration gradient.
Is it active or passive transport when deltaG is positive?
Active transport.
A negative delta G means it’s passive transport.
Where is Na+ concentration highest? Intracellular or extracellular? By how much?
Higher extracellular. 145mM vs 12mM
Where is Ca2+ concentration highest? Intracellular or extracellular? By how much?
Higher extracellular. 1.5mM vs 100nM
Where is Cl- concentration highest? Intracellular or extracellular? By how much?
Higher extracellular. 123 mM vs 4.2mM
Where is K+ concentration highest? Intracellular or extracellular? By how much?
Higher intracellular. 155mM vs 4mM.
The only of the four that is higher intracellular is K+!
How does PMCA work?
PMCA stands for Plasma membrane calcium ATPase. It’s a pump which uses active transport. ATP hydrolysis is undergone to make ADP and inorganic phosphate. This causes Ca2+ to be pumped out of the cell.
What is uniport?
When only one type of ion/molecule is transported in or out.
What other types are there?
Symport and antiport
What is symport?
When two different molecules or ions are transported in or out via same channel at same time.
What is antiport?
When one molecule or ion is transported out, and another molecule or ion is transported in.
What is the Na+K+ATPase? How does it work?
It’s called in lay term Sodium pump. It’s an antiport which used ATP to pump 2K+ into the cell and 3Na+ out of the cell. It uses active transport.
Why is the Na+K+ATPase important?
It generates the ion gradients that are used to allow secondary active transport and action potentials. However it is only a small contribution to resting membrane potential.
What is the Na+Ca2+exchanger dependent on (NCX)?
On the Na+ gradient generated by the K+Na+ATPase.
The K+Na+ATPase is used for another sort of antiport as well. Which?
Na+H+ transporter. Na+ gradient generated from Na+K+ATPase is used to transport H+ out of the cell.
The K+Na+ATPase is also used for a symport. Which?
The Na+ gradient generated by K+Na+ATPase is used to transport Na+ into the cell again along with glucose.
Give examples of Co-transport systems.
Na+K+ATPase
NCX (Na+Ca2+exchange)
Na+H+ exchange
Na+Glucose co-transport
Give an example of a clinical setting where this principle is important.
In cystic fibrosis a channel called CFTR doesn’t work which makes Cl- leave the cell to go to the lumen of for example the vas deferens and lumen of pancreas. When Cl- isn’t able to leave there will be a lower concentration of Cl- extracellularly. This means that as much water as should follow the Cl- won’t follow and the vas deferens and lumen of pancreas ends up with less water and thicker mucous for example. Digestive enzymes get stuck in the pancreas or on their ways to the gut and semen gets stuck in the vas deferens rendering one infertile.
How do transporters work in diarrhoea?
Protein Kinase A is activated by an infection such as vibrio cholera. This makes the Cl- channel to be stimulated and more Cl- is transported out of the cell into the lumen of the small intestines. This makes water follow.
