Biochemistry 440
Fall 2008
Problem Set 7
1. Formal oxidation numbers:
1a. Give the formal oxidation number of the carbon in the following compounds.
CH4, CH3OH, and CO2. Which is the most reduced form of carbon?
1b. Assign oxidation numbers to each carbon in glucose.
1c. Assign oxidation numbers to each carbon in pyruvate. Compare the oxidation state of
pyruvate to that of glucose.
2. In the fourth step of glycolysis, fructose 1,6 bisphosphate is cleaved to glyceraldehyde 3-
phosphate and dihydoxyacetone phosphate. Is this an oxidation? Why or why not? Explain
in terms of the oxidation numbers of the carbons.
3. The book calls the summed, overall standard free energy change of the first five steps of
glycolysis "endergonic". When these reactions happen in a cell, are any of them endergonic?
Explain.
4. You feed cells glucose that is labeled on the first carbon with 14C. Which carbon(s) of
pyruvate will be labeled after glycolysis is completed? Do the same for each carbon of
glucose.
5. This exercise will help you understand glycolysis: Suppose you set out to alter the glycolytic
scheme for the purpose of eliminating what appears at first glance to be an unnecessary
complication, namely the aldolase reaction in which the six-carbon fructose 1, 6-phosphate is
split into two three-carbon fragments. Such a notion has apparent merit. Since the
phosphorylation of fructose 6-phosphate to fructose 1, 6-bisphosphate is a preparatory step
for the aldolase reaction, it, too, could be eliminated, thus avoiding the expenditure of one
ATP.
Notice that glucose 6-phosphate can be considered analogous to glyceraldehyde 3-phosphate
(it just has more of an interior chain). Thus, this new scheme could involve a dehydrogenase
reaction analogous to that catalyzed by glyceraldehyde 3-phosphate dehydrogenase. Instead
of converting glyceraldehyde 3-phosphate to 1, 3 bisphosphoglycerate, this new
dehydrogenase would convert glucose 6-phosphate to 1, 6-bisphosphogluconate. We would
have:
A. Starting with glucose, devise a new glycolytic scheme whose first two steps are given above
and whose subsequent steps are to be exactly analogous to those of the real glycolytic
scheme, ending up with a compound whose oxidation state is identical to pyruvate. State for
