Session 3: Membrane Permeability, Transporters and Ion Channels Flashcards
What is a semi-permeable membrane?
A layer through which only certain molecules can pass
What types of molecules can permeate a lipid bilayer?
Hydrophobic molecules
Lipophilic molecules
Non-polar molecules
What cells have a lipid bilayer?
ALL cells
Passive transport of molecules through a membrane is dependent on what two things?
Permeability
Concentration gradient
Give 3 examples of the important roles of transport processes in the body
Maintaining intracellular pH
Maintaining ionic concentrations
Regulation of cell volume
Expulsion of metabolic waste and toxic substances
Generation of ion gradients in excitable cells
Why would reciprocating “flip-flop” and rotating carriers be very unlikely in a cell transport protein?
Thermodynamically not likely as it would take too much energy to achieve
Is a gated pore that carries out “ping pong” transport an efficient method of movement molecules across a membrane?
No, it is very slow
What can membrane transport proteins do instead of using inefficient “ping pong” transport?
Form channels which can open to allow molecules to pass in and out of the cell via facilitated diffusion
Channels that open in response to agonist binding are known as what?
Give an example
Ligand-gated ion channels
Nicotinic Acetylcholine Receptor
Channels that open in response to changes in ion current are called?
Give an example
Voltage-gated ion channels
Sodium (Na+) channel
On a Michaelis- Menten curve. How would you find the Vmax and the Km
The Vmax is the maximum velocity or rate
The Km is the concentration at half of the Vmax
What can we use to give a more accurate measure of Vmax and Km?
A double reciprocal plot
In relation to change in Gibbs free energy, passive transport is ______ and active transport is _______.
- change is passive transport (-deltaG)
+ change is active transport (+deltaG)
Whether molecules move across the membrane by active or passive transport is dependent on what two things?
The concentration ratio
The membrane potential
Active transport allows the transport of _______ and molecules _________ an unfavourable concentration and or electrical gradient
ions
against
True or false: Active transport can be direct or indirect
True
How does direct active transport differ from indirect active transport?
Direct active transport involves the transporters directly binding ATP and using the energy produced. Indirect active transport uses the energy stored in the concentration gradient that has been set up by direct active transport of an ion.
How does simple diffusion differ from facilitated diffusion?
Simple diffusion involves a molecule being transported across the lipid bilayer whereas facilitated diffusion involves a channel or a carrier to transport the molecule across
What are the approximate intracellular and extracellular concentrations of Na+?
Intracellular: 12mM
Extracellular: 145mM
What are the approximate intracellular and extracellular concentrations of Cl-?
Intracellular: 4.2mM
Extracellular: 123mM
What are the approximate intracellular and extracellular concentrations of Ca2+?
Intracellular: 10^-7 M
Extracellular: 10^-3 M
What are the approximate intracellular and extracellular concentrations of K+?
Intracellular: 155mM
Extracellular: 4mM
Transport of an ion/molecule can be described as what three things depending on the number of ions and the direction of their movement?
Uniport
Symport
Antiport
Symport is a type of co-transport that does what?
Transports different ions/molecules across the membrane at the same time, in the same direction
