How do molecules "know" how to move within a living cell?

Question

This is a simple question but one I find puzzling.

Tiny molecules go through our blood, and capiliaries, and within the cells themselves.
How do they get guided to the right place?

For example, if a tiny mitochondria accepts and produces various proteins (which are extremely small, even on the cell level) How do they get guided to the right place?

I don't buy the argument that they bounce around inside a cell until they attach correctly to some other structure...its too unlikely....what is guiding these molecules to the right place?

Any creative insights would be greatly appreciated.
thanx!

Answer 1

Living cells have much more complicated structure than one might expect.

There a lot of different factors guiding the molecules to different parts of the cell and even of the whole organism. Not all have been dicovered and there are more than one theories for some mechanisms.

There are many driving forces e.g. osmotic pressure, membrane potential, electrochemical gradients, oligomerization/polymerization, etc. Usually guiding something towards a certain direction requires energy and usually this means ATP hydrolysis in cells.
The way you guide it depends on the system.

The argument of simple diffusion that you mention does not always apply. The best example of this is the way proteins which bind to specific sites in the DNA manage to find their target.
Simple diffusion cannot account for what we see experimentally;simply too inprobable to bind with the speed we see, and thus "facilitated" diffusion is thought to occur.
This means that the protein might be diffusing in the cell (assume prokaryotic cellfor the sake of simplicity) but once it encounters DNA it binds to it very weakly through electrostatic forces and H-bonds, even if it is not its target site.
Then with different mechanisms like hopping, sliding etc it scans the DNA molecule until it finds its site. Thus it doesn't lose time by diffusing far away from the DNA as the simple diffusion model might suggest.

Similar mechanisms are thought to be possible for some protein-protein or protein-ligand interactions .
This is a bit different to what we are used as chemists working with small molecules: two small molecules collide and react only if they have the right energy and orientation;otherwise they bounce away. Here we are saying that they don't bounce far away but stay close enough to scan each other through weak interactions, searching for a possible reaction site.

Answer 2

That is the riddle of life, and the aim of biochemistry and anatomy. The cell is not just soup, it is quite highly organised, and little happens by accident when functioning well. Diseases happen when not functioning well. "The endoplasmic reticulum" is a ribbon winding through a cell that gives it basic structure. There are organelles, like mitochondria, and golgi bodies. The blueprint for everything living is the DNA that contains the genes in the nucleus: adenine, guanine, thymine, and cytoceine are all that is neccessary to contain the plans for life, with deoxyribose sugar as the rail in a double helix (spiral). The spiral staircase of life.
There is the outer cell mebrane. There are fluids and hormones and electrolytes and many other things that interact by flow, shape and electrical charge:
http://www.en.wikipedia.org/wiki/cell_metabolism
will start you out. Enzymes will also give clues. They help hold molecules in the right orientation to react together. Then they detach, and do it again!
http://www.brightplanet.com/deepcontent/tutorials/search/
will give you the tools to go as long as your curiosity
does not flag. Happy exploring!

Answer 3

First of all there are billions upon trillions of molecules in our bodies so it is VERY likely that they get where they are going. And second, the cells themselves guide the molecules to the right place inside them.

Answer 4

They do bounce around until they get to the right place.
For many molecules, efficiency is increased by selective mechanisms based physical or chemical properties such as size or charge. Their origin may also play a role in localisation.

Answer 5

actualy they do bounce around untill they attach correctly, i dont see why is that so hard to expect. but!, they do have litlle help by forces that interact among them. the thing is, every proces hapens so that total amount of energy in sistem would get lower. so if the molecul gets close to the correct position, it will turn around under influence of these forses so that the reaction would become posible, cause that will lower the energy within the sistem.

Answer 6

Hey! give somthing seedlike for creativeness,does seed know there is nothing more within his containing boundary, and it has to grow and go outside?.

Answer 7

ive been puzzled on this just as well, what is 'guiding'? hah, just like gravity, what is it???? whats actually pullin or pushing? but i think its God man for real. ima go research it a bit, peace...

Answer 8

they have macro brains! GASP!!

or they just have a nose that smells certain liquids till it finds the right scent