CASE FILES: BIOCHEMISTRY
Figure 14-2. The conversion of pyruvate to lactate by the enzyme pyruvate
dehydrogenase. The reaction, which is reversible, uses the reducing equiva-
lents from NADH and regenerates NAD+ for the continuation of the glycolytic
pathway when oxygen is limiting.
used by the cell. Energy needs must be met by catabolism of carbohydrates
through the glycolytic pathway. However, since under these anaerobic condi-
tions, pyruvate dehydrogenase, the TCA cycle and oxidative phosphoryla-
tion are compromised, only a fraction of the chemical energy that is obtained
from the oxidation of glucose under aerobic conditions is produced. Glucose
that is completely oxidized to CO2 and H2O under aerobic conditions will pro-
duce between 36 and 38 mol of ATP per mole of glucose depending on the
shuttle used to transport cytosolic reducing equivalents to the mitochondria.
Only 2 mol of ATP are produced per mole of glucose converted to lactate
through anaerobic glycolysis. The ATP needs of the cell are met by the
increased rate of the glycolytic pathway.
C O M P R E H E N SIO N Q U E ST IO N S
[14.1] Phil Hardy has decided to train for an upcoming marathon. Nearing the
age of 50, Phil figures that after he trains he should be able to maintain
a 9 minute-per-mile pace, which would mean that he would finish the
race in approximately 4 hours. Given that he would be adequately
hydrating himself at the various water stations along the way, as he is
about to finish the 26 mile 385 yard course, what is the primary fuel
that his leg muscles would be using?
A. Fatty acids from the blood
B. Glycerol from the blood
C. Glycogen stored in muscle
D. Glucose from the blood
E. Ketone bodies from the blood