CASE FILES: BIOCHEMISTRY
B IO C H E M IS T R Y PE A R L S
Most of the energy that the body requires for maintenance, work,
and growth is obtained by the terminal oxidation of acetyl coen-
zyme A (acetyl-CoA), which is produced by the catabolism of
carbohydrates, fatty acids, and amino acids.
The oxidation of acetyl-CoA is achieved by mitochondrial enzymes
that make up the tricarboxylic acid cycle (TCA cycle, also called
the citric acid cycle or the Krebs cycle).
When the ETS and oxidative phosphorylation are compromised by
a lack of O2, cytosolic levels of ATP drop, while ADP and AMP
The flow of glucose through the glycolytic pathway is increased
because of allosteric activation of phosphofructokinase and pyru-
vate kinase by the drop in ATP and rise in AMP concentrations.
The four carbon intermediates of the TCA cycle may be replenished
or increased by metabolites of the glucogenic amino acids enter-
ing at a-ketoglutarate, succinyl-CoA, or oxaloacetate. In addi-
tion, the C4 pool can also be increased by the carboxylation of
pyruvate to oxaloacetate catalyzed by pyruvate carboxylase.
Beattie DS. Bioenergetics and oxidative metabolism. In: Devlin, TM, ed. Textbook
of Biochemistry with Clinical Correlations, 5 th ed. New York: Wiley-Liss, 2002.
Harris RA. Carbohydrate metabolism I: major metabolic pathways and their con-
trol. In: Devlin TM, ed. Textbook of Biochemistry with Clinical Correlations,
5th ed. New York: Wiley-Liss, 2002.