What is secondary active transport?

[sameeralord]

Hello,

Ok I researched it but I don't understand. What I understand is that when one molecule normally diffuses(high to low) another molecule from a (low to high gradient) attaches to the carrier protein. How does this molecule attach without ATP? I don't get it. Any help would be appreciated. I'm talking about membrane transport of course!

 

[Smachine]

Im not sure which part of the mechanism are you not understanding, but the general idea is quit simple. ATP energy is spent to create concentration and possible also electrical gradient for one substance across cell membrane and the other substance is transported together with the first substance by using this stored energy. Good example is SGLT1 glucose transporter protein, that moves Na⁺ ions in the direction of their electrochemical gradient and glucose molecules against their concentration gradient. Energy for this still comes from ATP, but is stored as electrochemical gradient and then its used for transport purpose.