TBR CBT 2 Question

Haha I was wondering this too! But I have just sort of committed it to memory! Someone help us please! As for the antiport symport, I know that anitport is secondary active transport for sure because at least one of the ions is moving across its concentration gradient. As for symport, that confused me. I did some reading on the symporter and discovered that it is also considered to be a method of secondary active transport; although both ions/molecules are pushed in the same direction, one is still flowing against its concentration gradient while the other is flowing down its concentration gradient.

 

Doesn't the secondary active part of the sym/anti port depend on the energy of facilitated diffusion? Maybe that's what it's referring to.

 

They can be for both! The primary/secondary transport, you have to look at where the energy is coming from and how the gradient is being set. If you have two things that are going down the same channel, down their own concentration gradients, it's facilitated diffusion. If you have energy being used to elsewhere to create the gradient for either ion, it's secondary active. Does that help? Let me know if I'm unclear (or wrong!) lol

 

Someone else want to explain the beta linkage conundrum i.e. why we can't digest cellulose but some of us can digest lactose via the lactase enzyme? I know we can digest alpha linkages like starch

 

I feel like an antiporter has to be an example of active transport because the definition of active transport is moving something against its concentration gradient and because that is always happening for at least one of the molecules in an antiport system, then it has to be active transport, specifically secondary active transport because there is no DIRECT coupling to ATP. Thoughts?

 

This is often a problem if you memorize very general comments and try to apply them universally. We lack the enzyme to cleave a beta-1,4-linkage between glucose residues. This does not mean we lack an enzyme for other beta-1,4-linakges.

Lactase cleaves the 1,4-beta linakge from galactose to glucose, so we do have at least one enzyme in our body that can cleave beta linkages.

 

Nope. Not everything has the same concentration gradient. Think about Na/K in neuronal cells. Na comes in, K goes out. If you had them going through the same channel, and imagine that ATP is not creating the gradient, then you don't have secondary active. You have facilitated. Secondary active/active is all about whether energy is being used or not.

 

Hmmm, I'm confused. There is still energy but it's in the form of the electrochemical gradient of the ion. Isn't that why the often call secondary active transport ion-coupled transport?