Why does active transport need energy?

[ItIsYaBoyGaryOak]

For a Na K pump, as per wikipedia's diagram, the binding of sodium opens an ATP binding site. ATP hydrolysis changes the pump conformation and releases the sodium. The new conformation binds potassium, which when bound, releases the phosphate and reverts the conformation starting it over again.

 

What is the ATP hydrolysis step for? I understand that the kinase is moving the phosphate from ATP to the transporter, but is that required for a conformational change? would an ionic interaction or some other binding that doesn't involve chemical change work to change the conformation as well?

Enzymes can change conformation from just binding, in this case potassium binding changing the ATP active site thus releasing the phosphate.

Why can't the system just use inorganic phosphate or some other ligand instead of ATP?

For example:

Na binds, opening up Pi site, Pi binds changing conformation, Na released, K binds, K binding releases Pi, conformation reverts.

Obviously if passive transport up a concentration gradient were possible everything would do it

what is the ATP hydrolysis doing to cause a conformational change that couldn't be achieved without energy / with a regular ligand?

 

 

In an example protein, it binds A, B, and C, but only A sites are open to begin with and C is bound.

When A binds, C is ejected and B sites open. When B binds, A is ejected and C sites open. When C binds, B is ejected and A sites open.

This system has a constantly changing conformation that doesn't need energy or a reaction to change shape.

Why can't that be applied to transporters so that transport only goes in one direction?

 

Simplest form of my argument:

Conformational change does not always require energy

Transport only requires conformational change

Transporters that only work one way are mechanistically possible

why is energy usage required for transporters to only work in one direction if regular binding without energy usage can change conformation?

[Vmedvil2]

12 hours ago, ItIsYaBoyGaryOak said:

For a Na K pump, as per wikipedia's diagram, the binding of sodium opens an ATP binding site. ATP hydrolysis changes the pump conformation and releases the sodium. The new conformation binds potassium, which when bound, releases the phosphate and reverts the conformation starting it over again.

 

What is the ATP hydrolysis step for? I understand that the kinase is moving the phosphate from ATP to the transporter, but is that required for a conformational change? would an ionic interaction or some other binding that doesn't involve chemical change work to change the conformation as well?

Enzymes can change conformation from just binding, in this case potassium binding changing the ATP active site thus releasing the phosphate.

Why can't the system just use inorganic phosphate or some other ligand instead of ATP?

For example:

Na binds, opening up Pi site, Pi binds changing conformation, Na released, K binds, K binding releases Pi, conformation reverts.

Obviously if passive transport up a concentration gradient were possible everything would do it

what is the ATP hydrolysis doing to cause a conformational change that couldn't be achieved without energy / with a regular ligand?

 

 

In an example protein, it binds A, B, and C, but only A sites are open to begin with and C is bound.

When A binds, C is ejected and B sites open. When B binds, A is ejected and C sites open. When C binds, B is ejected and A sites open.

This system has a constantly changing conformation that doesn't need energy or a reaction to change shape.

Why can't that be applied to transporters so that transport only goes in one direction?

 

Simplest form of my argument:

Conformational change does not always require energy

Transport only requires conformational change

Transporters that only work one way are mechanistically possible

why is energy usage required for transporters to only work in one direction if regular binding without energy usage can change conformation?

The simplest terms to think about it in are this "Some chemical reactions require energy to initiate the reaction" , with enzymes and proteins some reactions that they catalyze require energy too. To pump something the opposite direction as the gradient requires energy as well. This is because it requires work to be done on the item of interest to produce the function of the protein, anytime this is the case ATP will be used to release the energy required to do the work. It is because the chemical reaction or movement requires energy that ATP is used, proteins do not just generate energy from nothingness, let's say that the reaction requires 10 millijoules to initiate the reaction then the enzyme/protein will use 10 millijoules worth of ATP to make the reaction happen if that is the function of that protein, the active site may lower the amount of energy required to do that reaction as a catalyst however energy may still be required to actually initiate the reaction. This can be applied to transport as well, if the protein requires 10 millijoules of energy to move the item of interest up a 10 millijoule gradient then 10 millijoules of ATP will be used to move the item of interest up that gradient by the protein. The reason it works that way is because of evolution and how the proteins evolved to work in that way. In a alternate biochemistry, we may find that they work in no way like Terran proteins work dealing with active transport and energy requiring reactions. This being said, if you have found a way to construct a more efficient biochemical pathway or protein then that is found in nature it may be worth actually constructing it in real life using DNA synthesis. If it works to do active transport without energy I am sure someone someday will genetically modify themselves to express that protein or biochemical pathway.

Edited October 13, 2020 by VictorMedvil