Difference between channel proteins and carrier proteins

[Dory]

I tried reading my textbook, looking it up online, and asking a private teacher. Most explanation were vague, contradicting, or non-elucidating. I need help figuring out the difference straight and clear.

Anyone?

[Feck]

any of this book help ?

http://www.ncbi.nlm.nih.gov/sites/entre ... &bname=mcb

[natselrox]

There can be whole threads on this. But to be short, a carrier protein is one that after binding to its substrate, changes it's conformation so as to make the substrate face the other side of the membrane. The channel proteins are like gates that can be opened by a specific mechanism (voltage gated, ligand gated etc.) so that they allow the passage of a specific type of substance.

[Dory]

There can be whole threads on this. But to be short, a carrier protein is one that after binding to its substrate, changes it's conformation so as to make the substrate face the other side of the membrane. The channel proteins are like gates that can be opened by a specific mechanism (voltage gated, ligand gated etc.) so that they allow the passage of a specific type of substance.

Amusingly enough that was my initial theory until I was confused by my private teacher. He seems smart, but he was way off then. He claimed that carrier proteins were either outside (intracellular fluid) or inside the membrane (cytoplasm), but not within the membrane like the channel proteins.

[Dory]

He also claimed that all transport proteins change their conformation.

[natselrox]

He also claimed that all transport proteins change their conformation.

At least that part is true.

[natselrox]

I'll send a PM to GfL. He is the pro on this one.

[GenesForLife]

Well, AFAIK the definitions involved are solely functional, in that carrier proteins bind to a substrate and help it to be transported , whether this is intracellular or intercellular doesn't matter, and they are basically capable of independent movement (hence the ability to carry their substrates), they can however, be integral transmembrane domains too, and can function like a kind of rotating door..

Channel proteins are always localized in membranes, and span them, they allow the channeling of substances in and out but don't themselves carry any substrate in the way carriers do, these are also usually involved in passive diffusion, in which case the proteins involved are called Porins.

So, it would appear...

1) Carrier proteins involve a complete change in orientation, usually after the substrate is bound, and this change in orientation leads to substance transport.

2) Channel proteins don't involve a complete change in the orientation of the whole protein, just a change between an open conformational state and a closed one, usually based on third party stimuli (voltage gated channels come to mind)