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Solving Feedback Regulation Problems

Solving Feedback Regulation Problems


Imagine that you are a biochemist studying the synthesis of glycine. Shown below are the structures of the chemical intermediates in the synthesis of glycine. You know that the pathway starts with 3-phosphoglycerate and ends with glycine.

a) Construct a reasonable pathway (it need not be the one actually used by living organisms) for the synthesis of glycine from 3-phosphoglycerate, showing the order of the given intermediates. Briefly describe the chemical transformations involved (you need not know the mechanism, "replace this OH with H" will be sufficient).

b) Given that 3-phosphoglycerate is used by several other cellular pathways, while the other molecules are unique to glycine synthesis: which enzymatic step(s) in your pathway would you expect to be inhibited by glycine?

The simplest assumption is that a group of atoms would not be put on, removed, and put back on later. This rule is true in this case, but not necessarily true in all cases. One possible pathway (and the one actually used) is listed below:

step 1 - 3-phosphoglycerate; turn H-C-OH to C=O

step 2 - 3-phosphohydroxypyruvate; turn C=O to H-C-NH3

step 3 - 3-phosphoserine; turn -(PO4)2- to -OH

step 4 - Serine; turn -CH2-OH to -H

b) Given that 3-phosphoglycerate is used by several other cellular pathways, while the other molecules are unique to glycine synthesis: which enzymatic step(s) in your pathway would you expect to be inhibited by glycine?

The first step unique to the synthesis of a particular product is usually inhibited by the end product. In this case, step 1 will be inhibited by glycine.


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