Energy And Passive Transportation:

[Mr.Smoke]

Since, we know that If one goes up, or along force P.E stored in body. In order to clearify this statement I am giving an example:
If we go upto the stairs, P.E stored in our body.
Similarly, when molecules are at high chemical gradient than (P.E should be present in Molecules ) why not it consist of energy, a.c to above example there must be P.E.

Give your Comments,
I need It.

Mr.Smoke.

[Mr.Smoke]

And according to Physics in order to do something, cover a distance... work must be done, and work can't do without energy. So how can molecules be transported in Passive transportation with-out energy.

[blazerUAB]

First off there their are different forms of potential energy. In your stair example the potential is due to gravity. The potential across a membrane is do not to Gravity, Elasticity but to Entropy. The second? law of thermo states that our universe proceeds in a direction to increase Entropy or Randomness. A concentration gradient is not random and will omve in a direction that will increase Entropy unitl equilibrium is reached. Equalibrium is maxium entropy.

[blazerUAB]

Entropy is not a form of potential energy but a general law that drives many chemical and biological process. Sometime the potential across a membrane can be due to the charges on the atoms present. This is a form of electric potential and is measures in Volts.

[2810712]

see in passive transport we don't use ATP-energy...but energy is required... which may be provided by electrostatic forces and in absence of any such force the proability that the molecules will remain on one side is very very less[ this is what 2nd law of thermodynamics tells us].

[Mr.Smoke]

Thanks, Means My Brain started working.
Gud to know that Passive transport required energy but not in ATP form but in electrostatic forces. Can you give me reference of this statement from any book. Because my teacher stated that there is no requirement of energy in Passive Transport.
Well blazer can you tell me about Entropy further, can we say it is a form of energy.
Thanks

[MrMistery]

there is no requirment of energy from the outside. Energy is still needed, but it comes from the substances that are moving according to entropy. It is the same thing that happens when a gas is let into a room. It's molecules spread across the whole room. Same thing, if the membrane is permeable for that particular substance then the molecules will tend to fill all the space they can and reach termodynamic energy.
Actually, passive transport causes the release of free energy, which can be used in some special purposes by the cell: ATP synthesis, secondary active transport etc
Free energy released by passive transport can be calculated from the following formula: ΔG=ΔGc+ΔGm
ΔGc=-RTln(c2/c1)
ΔGm=-nFΔψ

ΔGc is the free energy rezulted from the chemical gradient. in the formula, R is the universal gas constant and T is temperature measured in kelvins.All molecules with an uneven distribution have a concentration gradient.

ΔGm is the free energy rezulted from the electrical gradient. The F is the Faraday constant and the Δψ is the difference in potential measured in milivolts. Only ions have an electrical gradient.

Tell that to your teacher, and you'll probably get an A

[2810712]

That was v. nice reply Andrew.
And now it is clear that atleast one of the gradients[ electrical & chemical] need to be followed to get the process of diffusion feasible.
IT can also be put like only one may also be enough to have passive diffusion, u just need ΔG {=ΔGc+ΔGm } negative...

one clearence required for me-
i think the total free energy released is not absorbed by the secondary ion transporters or the ATPizers...otherwise the net process will not be feasible. is this corect. or it occurs like an equilibrium thing ΔG = 0, which would be better from efficiency pt. of view... if itsnot the case then, why?

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hrushikesh

[MrMistery]

Yes, you are right. A substance can diffuse down it's concentration gradient if it's a very big gradient while actually difusing up it's electrical gradient(if one delta G is more negative than the other delta G is positive, so to speak)

I don't know exactly if all the free energy released is used by the secondary active transport. But my experience with cell biology tells me that nothing in a cell has a 100% efficiency. So, my answer, strictly as an opinion would be that no, delta G is not 0, it is a little positive...

[2810712]

means in ideal case the Gchange is 0? i thought it will be still less than zero...and not an equilibrium like thing...




hrushikesh

[MrMistery]

yeah.. sorry, i meant a little negative. I agree with you..