[rleung]

Hi,

I know this isn't really too much of biochemistry, but I thought I would try my luck in this forum if anyone has an idea...It says in my textbook that direct active transport and indirect active transport can be differentiated by their requirement for metabolic energy, but I don't quite see that. Don't they BOTH require metabolic energy (since they both are forms of ACTIVE transport)? For example, direct active transport requires the energy that is liberated when ATP is hydrolyzed to ADP, while indirect active transport requires that one solute be moving DOWN its gradient in order to move the other solute AGAINST its gradient?

The only way that I can see that metabolic energy is required for one but not the other is if, by metabolic energy, they mean solely the free energy liberated by the hydrolysis of ATP and not free eenrgy generated from an ion going down its gradient....

Thanks so much!  I appreciate it

Ryan

[Yggdrasil]

That's the basic difference between direct and indirect active transport.  Direct active transport uses "metabolic energy" (e.g. energy from the hydrolysis of ATP) directly, while indirect active transport uses the metabolic energy indirectly because they are not directly powered by ATP hydrolysis.  So, "metabolic energy" is required for both forms of active transport; the difference is just in whether the transport is powered direcly by ATP or not.

It may seem like somewhat of a weird, arbitrary, or useless classification but that's how biology is 

[rleung]

ahhh..I see.  Thanks so much

[Equi]

I only know these as primary and secondary active transport.

Primary via: chemical reactions (redox, hydrolysis), photosynthesis
Secondary via concentration gradients (Protons, Sodium)