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Team:Paris Bettencourt/Modeling/Assisted diffusion
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=== Starting from an analogy === | === Starting from an analogy === | ||
| - | Immagine two bottles of gaz connected by a tube. The fist one have an higher pressure than the second one. In the first one, diluted in the gaz, there are a few molecules of another nature | + | Immagine two bottles of gaz connected by a tube. The fist one have an higher pressure than the second one. In the first one, diluted in the gaz, there are a few molecules of another nature. We follow the destiny of these molecules. |
| - | When you open the tape, the bottle with a higher pressure will equillibrate with the other one my moving a certain quantity of it's | + | When you open the tape, the bottle with a higher pressure will equillibrate with the other one my moving a certain quantity of it's particles through the tube in the direction of the second bottle. These moving molecules will drag with them the copoment diluted in the gaz and a few of these molecules will be transported to the other bottle. |
=== From the analogy to the biology === | === From the analogy to the biology === | ||
Revision as of 18:28, 1 September 2011
Contents |
Introduction to the model
The diffusion through the nanotubes is a fast process. This speed can be partially explained by the passive diffusion through the tubes. But what if it is faster? The article from Dubey and Ben-Yehuda suggests that the diffusion is an active process. Several points can be opposed to this statement:
- First, the diffusion is happening with molecule of different natures, that have nothing to do with the natural compoments of a cell
- Unlike the mamalian cells, the tube seems to have no "railroad" design for such a transport
The question is: can we immagine a process that is faster than passive diffusion but does not rely on specific interractions?
The answer is probably yes, and in this page we propose a new model, really challenging for the mind, but that can play a role in the diffussion process through the nanotubes.
General physical concepts and Hypothesis
Starting from an analogy
Immagine two bottles of gaz connected by a tube. The fist one have an higher pressure than the second one. In the first one, diluted in the gaz, there are a few molecules of another nature. We follow the destiny of these molecules.
When you open the tape, the bottle with a higher pressure will equillibrate with the other one my moving a certain quantity of it's particles through the tube in the direction of the second bottle. These moving molecules will drag with them the copoment diluted in the gaz and a few of these molecules will be transported to the other bottle.
From the analogy to the biology
Of cource, the cell is not a bag of liquid under pressure. The water is equillibrated at both sides of the exterior membrane. the pressure we are dealing with is not water or osmotic pressure (that is a "passive diffusion thermodynamical pressure"). There is a part of the cell we do not immediately think about that can undergo a huge variablilty of pressure: the membrane!
Let's evaluate the constraints that the membrane underdo. First, as it is a gramm positive bacteria, the external sugar envelopp impose the shape of the bacteria. On the other hand, the osmotic pressure is pushing the membrane against the sugar wall. Inside the membrane, the number of phospho-lipids is fixed by the state of division on the cell.
Though, a phospholipid is somehow behaving as a gaz trapped in a bottle. The ospotic pressure and the sugar layer are the bottle, and the number of particle trapped is giving thhe pression. This variation of pression can be important if the cell has just devide or if the cell is about to devide.
When the cell enter of communication, a flow of molecule can pass from the cell that have the highest membrane pressure to the other one. This is happening, when phospholipids are running around the tube.
But the tube is small and water has its own viscosity. If the pipe is moving, the water inside willfollow, with a Poiseuil shape sliding. Constituents diluted in water will move from one cell to another unidirectionally and faster than simply diffusing. This is a fast process that we have named after the "active" and "passive" diffusion, the "assisted diffusion"
