Minimals: membrane transport Flashcards
What does it mean that lipids are amphipathic?
They consist of hydrophobic and hydrophilic parts
What is the permeability constant?
The permeability constant is the amount of material transported through the membrane per unit surface in unit time due to unit concentration
What are the possible forms of motion of a lipid molecule in a membrane?
Lateral diffusion
Rotational diffusion
Transmembrane flip-flop
Flexible motion of fatty acid side chains
What are the possible phase states of biological membrane?
Gel phase
Liquid crystal/fluid phase
What changes in the properties of the fatty acid side chains increase the transition temperature of a membrane?
Increase in the saturation of fatty acid carbon-carbon bonds
Increase in the length of the fatty acid side chains
How does cholesterol change the fluidity of lipid membrane?
Below the phase transition temperature it usually increase, above the phase transition temperature it decreases
What is the magnitude of the lateral diffusion constant of lipids and proteins in biological membranes?
Lipids 10^-8 ~ 10^-9 cm^2/s
Proteins 10^-9 ~ 10^-12 cm^2/s
Which methods can be used to measure the lateral diffusion of proteins in biological membranes
Fluorescence recovery after photobleaching (FRAP)
Single particle tracing (SPT)
Fluorescence correlation spectroscopy (FCS)
For what kind of molecules is the permeability of biological membranes the highest?
For small, uncharged, apolar molecules.
Eg. O2 N2
How can membrane proteins be classified based in their function
Transport and channel protein
Receptor and signal transducing protein
Enzymes
Structural membrane proteins
What is passive transport
Transport processes driven by the electrochemical potential gradient which do not need active metabolism
What is active transport
Transport processes that results in material flow against their electrochemical potential gradient at the expense of energy utilization.
What is primary active transport
The transporter pumps ions/molecules across the membrane against their electrochemical gradient using energy from ATP hydrolysis o
What is secondary active transport
Secondary active transport moved ions/molecules across the membrane against their gradient using energy stored in the gradient of another ion created by primary active transport mechanism
What is simple diffusion across biological membrane
The passive transport of small and lipid-soluble molecules across the membrane
What is facilitated diffusion
The passive transport of meme brand impermeant ions/molecules across the membrane aided by transport proteins(ion channels or carriers) molecules
What are the properties of facilitated or carrier mediated diffusion?
Transporter proteins specifically bind the transporter molecules
The transport can be selectively inhibited
The flux of transport can be saturated over a given concentration of the transported material
What kind of ion channels do you know based in their mode of activation
Ligand gated ion channels Voltage gated ion channels Second messenger gated ion channels Mechanical deformation (stretch) activated ion channels
What is the function of ionophores
They promote the selective transport of ions through lipid membrane
How can ionophores be grouped according to the mechanism of ion transport
Carrier ionophores
Channel forming ionophores
List the factors contributing to the maintenance of quiescent membrane Potential
Diffusion potential
Donnan potential
Active transport by ion pumps
What is the equilibrium potential of an ion?
The membrane potential where the net flux of the given ion is zero.
The system is in thermodynamic equilibrium for the given ion.
Are the ions on the two sides of the membrane of a living cell in thermodynamic equilibrium? Why?
No. There is no thermodynamic equilibrium because the net passive flux of a given ion is not zero at the resting membrane potential.
Give the definition and the unit of flux
Flux (J) is the amount of transported items across unit cross section area per unit time. Unit: mol/(m^2s)
Give the definition and unit of conductivity
G(conductivity)=1/R
R is resistance
Unit: 1/omega=Siemens(S)
Define the action potential and interpret the ionic basis of its generation.
The action potential is a characteristic, time-dependent change in the membrane potential as a result of time and membrane potential dependent changes in the ion permeability so of the membrane. In the depolarization phase the Na+ permeability is dominant, the subsequent depolarization is the result of concurrent decrease in Na+ permeability and an increase in Ka+ permeability.
