Transport

Memory Hack💡

Active transport: You need energy to be active and move around much like how active transport requires energy input. 

Passive transport: Think of a "passive" person, who just goes with the flow, as passive transport does not require energy input and will move freely as a gradient. 

Notes

Active transport requires energy to move something against its gradient. Think… if you are being active, you are going to need an energy input. This is the same for active transport! I also sometimes need a nudge to start exercising… so I think of active transport as moving something against what they want to do. 

There are two kinds of active transport. Firstly, primary active transport, which utilizies ATP as the energy source to move molecules. An example of this is the Na+/K+ pump. 

• This pumps 3 Na+ molecules in, and 2 K+ molecules out. 

• To do this, ATP gets dephosphorylated (gives us our energy input!)

• Why is it important? It allows for the maintenance of the membrane potential. 

On the other hand, secondary active transport uses one natural gradient to drive the transport of another molecule without a natural gradient. This can be done using a  symporter (sym→ same), meaning both gradients move in the same direction. Or, an antiporter (anti→ different) which moves them in opposite directions. For example, if you were utilizing a symporter, both molecules would be transported into the membrane, where an antiporter would have one going on and one coming out. 

Example: Na+ glucose symporter (remember, this means it moves in the same direction!) 

• The natural Na+ gradient wants to move Na+ to the other side of the membrane, so, glucose, which does not want to be transported to the other side, “buddies up” with him, and passes over. 

  • • In this scenario, imagine that you are taking public transport that requires you to scan a card and pass through a gate (like the T in Boston). If the person in front of you scans their card, and you move fast enough, you can squeeze in as one person. This is true for secondary active transport. The first person (Na+) scans their card (energy from gradient) and you (the glucose) squeeze in on their dime to save money (energy). 

Passive transport: To move something along a gradient with no energy barrier. 

• For passive transport, I like to think of my older brother. He is super “passive”, and will just go wherever you take him as long as he doesn’t have to be in big crowds. Passive transport is the same, as long as they are going somewhere they wouldn’t mind being (energetically moving down a gradient) they will do it, and it takes no energy input for them to do so.