Chemistry 332 - Spring 1996
Elements of Organic Chemistry II
Homework, Chapter 17 - Metabolism
McMurry, pp 527-529:
Problems 17.10-21,24-29
Examine each of the 8 steps in the citric acid cycle shown on page 521.
For each step, identify whether the reaction involved includes one or more
of the following reaction types: oxidation, reduction, addition, elimination,
substitution.
For each step, identify the functional group(s) that undergo change in the
reaction.
For oxidation/reduction reactions, indicate what gets oxidized and what
gets reduced.
Note that some steps are actually a combination of more than one reaction,
and it would be most helpful to describe each one separately.
Example: Step 1 (oxaloacetate to citrate) is an addition - specifically
a nucleophilic addition of the alpha position of acetyl coA to the ketone
group of oxaloacetate.
Step 2 (citrate to isocitrate) is an isomerization of an alcohol group from
one position to another, but it is accomplished by a dehydration (elimination)
followed by a hydration (addition).
Step 3 (isocitrate to alpha-ketoglutarate) is an oxidation of an alcohol
to a ketone (NAD+ gets reduced to NADH) as well as a decarboxylation (elimination
of CO2).
Step 4 (alpha-ketoglutarate to succinyl CoA) is a decarboxylation (elimination
of CO2) and an oxidation of the ketone to a carboxyl group (NAD+ gets reduced
to NADH) and a substitution of CoA at the carboxyl group.
Step 5 (succinyl CoA to succinate) is a hydrolysis of the CoA thioester
group (substitution). The reaction releases energy and an ATP is made from
ADP.
Step 6 (succinate to fumarate) is an oxidation (or elimination of H2)
to put in the double bond (FAD gets reduced to FADH2).
Step 7 (fumarate to malate) is a hydration (addition of water).
Step 8 (malate to oxaloacetate) is an oxidation of an alcohol to a ketone
(NAD+ gets reduced to NADH).