Transporters Flashcards
How have gene families of transporters evolved?
There are 1289 genes for transporters and channels, together termed the TRANSPORTOME (4%of genome) with 406 ion;883 transporters
These are organized into super families such as the solute carrier family (SLC)
What is the Michaelis-Menten equation
describes SATURABLE TRANSPORT.
V= Vmax x [S]/Km + [S]
[S] of the CIS face
At V max; all the binding sites are occupied.
At Km (the constant) 50% of all sites occupied.
How do Km and V max provide information about the transporters function?
Facilitate transport is more rapid than simple diffusion, BUT it is SATURABLE (at Vmax)
At low substrate concentration, lower than the Km value volume of solute taken up is proportional to solute concentration.
Where he solute concentration is greater the the Km value, volume will EQUAL VMAX
Competitive effects on the transporter
INCREASES Km; as graph is initially more steep;
NO Change in V max (as it levels off at same level as control)
Non-competitive effects on the transporter
DECREASES v max (as it levels off below the maximium volume of the control)
NO CHANGE in Km
Describe different channel types in the membrane
Diffusion, facilitative Cell membranes have LOW diffusional permeability to many vital biological solutes including inorganic ions, sugars and amino acids. via different types of channels:
TRANSPORTERS (carriers/permeases/pumps)
water filled (aqueous diffusion)
facilitative
active transport (ATP dependent)
COUPLED transport (exchange)
How can the flux equation J1-2 = D.A.(change in c)/x
be used to increase solute movement across the membrane?
INCREASE Area (microvilli, alveoli)
DECREASE x Thickness (membrane already thin!)
INCREASE CHANGE IN CONCENTRATION (cell metabolism helps generate gradients)
INCREASE D (alter bilayer composition OR introduce “pores”)
Give some characteristics of pores
1) specific for certain substrates
2) saturable
3) specific inhibitors too
4) mediates the FLUX of a solute
How doe the rate of an ion channel compare to the transporter?
ion channel is MORE rapid (10-8 ions/s) and transporters 10-4/s.
This is due to greater specificity of the ion channel
ATP pumps even slower.
Give an example of a voltage gated ion channel?
Voltage-gated K+ channel when activated to OPEN allows for FAST/High flux of selected K+ IONS (singlefile)
ions are hydrated when selected and as a result the radius swells and increases.
Selectivity determined by the ions CHARGE AND SHAPE
channels can change shape or be gated,
What is the realtionship between ion diameter and mobility?
The larger ions are less mobile.
Why do smaller ions increase more when hydrated?
The smaller the ion radius means there is greater ion charge and so the greater the lattice enthalpy i.e. more exothermic. This effectively means the ions are closer together, so the centres of charge are closer together, hence a greater attractive force and more water molecules are attracted
Where is the CIS and TRANS interfaces in terms of ion transport?
CIS face is the side the ION is delivered
TRANS side, on the opposite face.
Describe symport/antiport transport (transporters)
When activated through substrate binding, there is a SLOW AND SMALL solute flux.
Selectivity determined by solute and BINDING-site on carrier protein.
It is slow because the transported has to REORIENTATE which is rate limiting.
Thus the reason (ion) channels are faster than transporters.
However, the antiport is faster than uniport)
Give details of the characteristic properties of uniport substrate binding site on the CIS and TRANS faces?
Cis-effects:
Saturability:- substrate molecules COMPETE for transporter binding-sites.
Stereospecificity:- Certain stereoisomers are BETTER FIT to binding site; very high affinities (like glucose) always taken in.
Trans-effects:
Exchange diffusion:- trans-substrate accelerates exchange
Counter transport:- trans-acceleration by a different substrate (hetero-exchange)
