The purpose of the citric acid cycle is to produce energy (both directly via GTP, and indirectly via NADH and . As such, energy can be though of to be on the products side of the sum of the reactions of the Krebs cycle. From Le Chatelier's principle, we know that if we want to inhibit a forward reaction, we can increase the concentration of the products. This will inhibit the forward reaction, and push the equilibrium to the left. Thus, in a high energy state, the ratio of ATP:ADP, like that of NADH: is high since both ATP and NADH are products of metabolism.

The entry point for acetyl CoA in the Krebs cycle is oxaloacetate. Acetyl-CoA and oxaloacetate combine to form citrate, which then continues through the cycle. Oxaloacetate is a carbohydrate, and so without carbs the acetyl-CoA can not enter into the Krebs cycle.

The regulated steps of the citric acid cycle are citrate synthase, isocitrate dehydrogenase, and alpha-ketoglutarate dehydrogenase. These steps are inhibited and stimulated by various products and reactants within the citric acid cycle. Succinate dehydrogenase is not regulated by products or reactants, and is therefore not rate limiting.

The citric acid cycle is amphibolic—that is, both anabolic and catabolic. Anabolism occurs when the citric acid cycle generates reduced factors, such as NADH and FADH₂. Catabolism occurs when the citric acid cycle oxidizes the two carbon atoms of acetyl CoA to carbon dioxide (CO₂).  

Glycolysis involves the conversion of glucose into pyruvate. Recall that glucose is a six-carbon molecule, while pyruvate is a three-carbon molecule. Thus for each molecule of glucose that undergoes glycolysis, two molecules of pyruvate are yielded. Next, pyruvate is converted into acetyl-CoA via the pyruvate dehydrogenase complex. Finally, acetyl-CoA enters the citric acid cycle, combining with oxaloacetate as the first step.

Enolase is the enzyme responsible for catalyzing the conversion of 2-phosphoglycerate into phosphoenolpyruvate. This reaction takes place during glycolysis. All other enzymes are involved in the sequence of reactions known as the citric acid cycle.

This is the correct sequence of intermediates in the citric acid cycle. Note that both citrate and cis-aconitase are substrates for the same enzyme, aconitase. The net yield of one turn of the citric acid cycle is: , and . The electron carriers then participate in the electron transport system along the inner mitochondrial membrane.

The citric acid cycle starts with the combination of a four-carbon molecule (oxaloacetate) and a two-carbon molecule (acetyl-CoA) to form a six-carbon molecule (citrate). Since the citric acid cycle is indeed a cycle, oxaloacetate must be regenerated. Thus, two molecules of carbon dioxide are produced throughout the citric acid cycle. The first molecule of carbon dioxide is produced during the conversion of isocitrate into alpha-ketoglutarate. This reaction is catalyzed by isocitrate dehydrogenase. Alpha-ketoglutarate, a five-carbon molecule, is then converted into the four-carbon molecule succinyl-CoA via alpha-ketoglutarate dehydrogenase, yielding another molecule of carbon dioxide. The remaining steps of the citric acid cycle do not involve any more production of carbon dioxide since both succinyl-CoA and oxaloacetate are both four-carbon molecules.

The enzyme alpha-ketoglutarate dehydrogenase catalyzes the conversion of alpha-ketoglutarate (5 carbons) to succinyl-CoA (4 carbons). During this step, one carbon is lost as carbon dioxide and one molecule of  is produced. This step is the second, and last step in the Krebs cycle in which carbon dioxide is formed. Recall that the starting material, oxaloacetate, is also 4 carbons long.

During the step in which one of the carbons of isocitrate is lost as carbon dioxide, one molecule  is also produced. This reaction is catalyzed by isocitrate dehydrogenase. This leaves a five-carbon molecule known as alpha-ketoglutarate. In the next step, alpha ketoglutarate dehydrogenase acts upon alpha-ketoglutarate and a carbon is lost as carbon dioxide and another molecule of  is produced. Later in the cycle, succinate dehydrogenase catalyzes the conversion of succinate to fumarate. This reaction produces one molecule of . The enzyme fumarase then converts fumarate to malate. The final step in the citric acid cycle is the regeneration of oxaloacetate from malate. Malate dehydrogenase catalyzes this reaction, which produces the third molecule of . Note that this is for one turn of the citric acid cycle i.e., for one molecule of acetyl-CoA. Each molecule of glucose yields two molecules of acetyl-CoA via glycolysis and pyruvate dehydrogenase complex.