Pyruvic Acid
Before entering the Krebs cycle, the pyruvic acid produced from the breakdown
of glucose must be further processed by converting it to acetyl-coenzyme A.
This is accomplished by the enzyme complex pyruvate dehydrogenase. CO 2 is
removed from pyruvic acid and the product is an acetyl group (a two carbon
group). The acetyl group is attached to coenxzyme A and the product is called
acetyl-CoA. The removal of CO 2 is called decarboxylation.The Krebs Cycle
The Krebs cycle(Fig, 5-2) is a series of biochemical reactions that occur in the
mitochondria of eukaryotic cells and in the cytoplasm of prokaryotes. The Krebs(^94) CHAPTER 5 The Chemical Metabolism
Acetyl CoA
Citric acid
Pyruvic acid
NAD+
CO 2
Isocitric acid
Alpha -Ketoglutaric acid
Fumaric acid Succinic acid Succinyl CoA
Malic acid
Oxaloacetic acid
CO 2
NAD+
CO 2
CoA
FADH 2
CoA
NADH + H+
NADH
CoA
NAD+
FAD ADPATP
GDP
GTP
NADH + H+
NAD+
NADH + H+
Fig. 5-2. The Krebs Cycle: Citric Acid Cycle