What is the process of facilitated diffusion?
In: Biology
Facilitated diffusion offers the advantage of resourcefulness. Such a Form of transport allows the cell to make use of concentration gradients. If a molecule is very highly concentrated outside the cell, you don’t need to carry each molecule and waste energy on it, you can just open a channel in the membrane and it goes through. But what if the molecule is big? Opening or keeping open a channel would thus allow the mobility of other smaller molecules or ions that you don’t want in the cell. The solution is a transporter or a carrier protein or uniporter, it grabs your molecule on the outside and flips it to the other side before releasing it. That way your transporter is passive yet specific. What about if you want to transfer something in but it’s slightly more concentrated inside, diffusion would result in efflux you can’t use that. But you also don’t want to spend extra energy, so.. You could just couple this to another process, say you happen to have an ion that is highly concentrated outside, and you have mechanisms to pump it out if it gets too much inside. So you couple your molecule of interest to enter along with the ion, so the gradient of the ion drives your molecule of interest against its concentration gradient. That’s a symporter. You can also use antiporters. Another advantage of such a system is that it can be wired to be dynamic. Say you only want to bring molecule X into the cell if Y is high enough outside (because the metabolism of X is dependent on extracellular Y). If you have a symporter, you would stop taking X in when Y is low, and this could useful. This happens all over the kidney, you transport so many ions along or against their gradients with other ions to create a well balanced result.
Edit: I realized I misread your question as “what is the importance of facilitated diffusion”. I answered with its advantages, if the definition is not readily obvious I can explain further.
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