You are studying a new organism from the muck at the bottom of Columbia Lake, wh

Question

You are studying a new organism from the muck at the bottom of Columbia Lake,

which you have named Ipso facto. I. facto is able to take up ribose from the growth

medium by the ribose transport protein (RTP). Your data indicates that the ribose

that is taken up is converted to ribose-5-phosphate (R-5-P) as it is transported into

the cell, and the phosphate on the R-5-P is from ATP. The uptake of ribose is not

inhibited by compounds that inhibit the Na+-K+

ATPase (the Na+-K+ pump).

1a). Draw a schematic of the RTP in the membrane, showing the various individual

stepsin ribose transport. Be sure to indicate where the membrane is, the inside

and outside of the cell, and how the ribose is converted to R-5-P? In your

answer, show the transport process (the answer here is more complex than a

drawing of hole in the membrane). For the next part of your answer, show a

detailed chemical mechanism for the conversion of ribose to R-5-P by ATP

Explanation / Answer

The pump, while binding ATP, binds 3 intracellular Na+ ions.[1] ATP is hydrolyzed, leading to phosphorylation of the pump at a highly conserved aspartate residue and subsequent release of ADP. A conformational change in the pump exposes the Na+ ions to the outside. The phosphorylated form of the pump has a low affinity forNa+ ions, so they are released. The pump binds 2 extracellular K+ ions. This causes the dephosphorylation of the pump, reverting it to its previous conformational state, transporting the K+ ions into the cell. The unphosphorylated form of the pump has a higher affinity for Na+ ions than K+ ions, so the two bound K+ ions are released. ATP binds, and the process starts again.

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