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Which is the correct option

Wed Nov 07, 2007 7:31 am

Atp molecules combine with carrier molecules and allow passage of substances

a) along concentratio gradient

b) against concentration gradient

c) both a and b

I think it should be b but the book says it should be c

Please specify which option is correct

Wed Nov 21, 2007 8:25 pm

Hmmm. I know ATP is required to move a substance against the concentration gradient. I know it isn't necessary for the movement of substances down the concentration gradient. My question is "What does your book mean by along?" If it means moving a substance from one place to another without bringing it into or pushing it out of the cell, then I guess C could work, but I doubt that is what it means. I haven't learned anything about movement "along" a concentration gradient in Cell Biology or Micro. Maybe you ought to ask the professor.

Wed Nov 21, 2007 11:27 pm

atp activated gates and atp powered pumps.

Thu Nov 22, 2007 2:15 am

But what does along the concentration gradient mean?

Thu Nov 22, 2007 3:48 am

probably just means with the gradient rather than against it.

Thu Nov 22, 2007 8:20 am

to move something along a concentration gradient means to move it down its concentration gradient(from high concentration to low concentration).

PS: no idea why the book says it should be c...

Thu Nov 22, 2007 10:32 am

hmm...about the utilization of ATP to move substrates along the conc gradient, I think it's because some substrates must be activated in order to go forward the membrane gate protein. And one of the activation process is phosphorylation of the substrates/protein.

I think that the example is the maltose transporter in E. coli which is a periplasmic-binding-protein transport system. When maltose move through the outer LPS membrane into the periplasmic space, it's bound with the periplasmic protein. Then, if the cell want the maltose to be further transported into the cell, then a transmembrane protein in the cell membrane must be activated in order to bound with this periplasmic glucose-protein and get the glucose transported inside. This activation then requires ATP and is one of the active transport.

Any opinion about this?

Thu Nov 22, 2007 11:31 am

could be what the guy asking the question had in mind....

Thu Nov 22, 2007 12:18 pm

Another example that I could think of is a PTS (phosphotransferase system) which is also utilized mainly in Gram+ bacteria.
In this system, it uses phosphoenolpyruvate (PEP) instead of ATP to phosphorylate glucose and get the glucose in through the specific transmembrane gate protein. But it's known that PEP will generate 1 ATP if it's converted into pyruvate.
I read this in Brock Biology Of Microorganisms 10th Ed. by Madigan et al (2003).
I think this is a good pic :D
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