Facilitated Diffusion Q

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This is probs a pretty basic question, but I haven't taken biochem yet so I'm a bit confused with facilitated diffusion involving a carrier protein. So the way I understand it, the solute binds to the carrier and induces a conformational change in the carrier. The chances of the solute binding is determined by the concentration of the solute, which is why the substance flows down a concentration gradient (more likely to bind on one side if there is more solute on that side). What I am confused about is where the energy for the conformational change is coming from. Doesn't the conformational change at least require heat energy? Because it is a form of passive transport, no energy expenditure is needed...but without energy how does the carrier protein go about changing shape?

Thanks!

Originally Posted by MedHopeful114

This is probs a pretty basic question, but I haven't taken biochem yet so I'm a bit confused with facilitated diffusion involving a carrier protein. So the way I understand it, the solute binds to the carrier and induces a conformational change in the carrier. The chances of the solute binding is determined by the concentration of the solute, which is why the substance flows down a concentration gradient (more likely to bind on one side if there is more solute on that side). What I am confused about is where the energy for the conformational change is coming from. Doesn't the conformational change at least require heat energy? Because it is a form of passive transport, no energy expenditure is needed...but without energy how does the carrier protein go about changing shape?

Thanks!

http://highered.mcgraw-hill.com/site...ion_works.html

Originally Posted by MedHopeful114

This is probs a pretty basic question, but I haven't taken biochem yet so I'm a bit confused with facilitated diffusion involving a carrier protein. So the way I understand it, the solute binds to the carrier and induces a conformational change in the carrier. The chances of the solute binding is determined by the concentration of the solute, which is why the substance flows down a concentration gradient (more likely to bind on one side if there is more solute on that side). What I am confused about is where the energy for the conformational change is coming from. Doesn't the conformational change at least require heat energy? Because it is a form of passive transport, no energy expenditure is needed...but without energy how does the carrier protein go about changing shape?

Thanks!

Any kind of passive transport works with the GRADIENT. By that I mean the "energy" so speak of comes from the formation of gradient. the gradient means that you do not need to input any energy and the delta G of the reaction is negative. The only time you use ATP is during active transport such as Na/K ATPase

So does the actual conformational change ITSELF require energy? I'm assuming that the overall effect of facilitated diffusion is an increase in entropy by "spreading out" the solute as much as possible, but at times doesn't the solute move from an area of lower concentration to an area of higher concentration, just not at as fast as the rate of solute moving from a higher concentration to a lower concentration? I guess I'm kind of thinking about it like a chemical reaction, where reactants are being converted to products and products to reactants, but not necessarily at the same rate. So when the protein undergoes a conformational change, is this isolated process favorable?

Originally Posted by MedHopeful114

This is probs a pretty basic question, but I haven't taken biochem yet so I'm a bit confused with facilitated diffusion involving a carrier protein. So the way I understand it, the solute binds to the carrier and induces a conformational change in the carrier. The chances of the solute binding is determined by the concentration of the solute, which is why the substance flows down a concentration gradient (more likely to bind on one side if there is more solute on that side). What I am confused about is where the energy for the conformational change is coming from. Doesn't the conformational change at least require heat energy? Because it is a form of passive transport, no energy expenditure is needed...but without energy how does the carrier protein go about changing shape?

Thanks!

Right. Any sort of transport pertaining to diffusion or passive transport, by definition, does not involve use of ATP hydrolysis either directly or indirectly.

The conformational change that occurs when the ligand binds to the membrane transporter protein is "powered" by the protein simply seeking its most thermodynamically stable orientation.

Given the various factors within the cell, the transport protein's affinity for the ligand could be quite high on the side of the membrane with the larger concentration of the ligand. This would make it more favorable to bind to the ligand.

One this binding takes place, however, the membrane transporter protein could alter its physical structure due to induced-fit binding or just a conformational change. Now, the protein may no longer have the same affinity for the ligand. Another consequence of this conformational change is that the transporter protein now may be able to achieve its most thermodynamically stable state by releasing the ligand on the other side of the membrane.

This long and enduring explanation just restates how natural processes seek out their most stable thermodynamic state and, as they seek this state, free energy may become available.