The Krebs cycle is very important for the production of the electron carriers NADH and FADH₂. NADH is produced in a higher quantity, partially due to the fact that it is more energetically favorable during the electron transport chain. During one turn of the Krebs cycle, one acetyl-CoA is used to generate a CoA residue, three NADH, one GTP, one FADH₂, and two carbon dioxide. Each glucose molecule produces two acetyl-CoA, fueling two turns of the Krebs cycle and doubling these amounts.

The net products of glycolysis are 2 pyruvate, 2 ATP, and 2 NADH.

For every two molecules of pyruvate that enter the Krebs cycle, six molecules of NADH are generated. Only four molecules of carbon dioxide, two molecules of FADH₂, and two molecules of ATP (GTP) are produced. The reason this has significance is because NADH is an important electron carrier that will help produce large amounts of ATP during the electron transport chain. The primary purpose of the Krebs cycle is to generate large amounts of this electron carrier in order to fuel the electron transport chain and oxidative phosphorylation, which is eventually responsible for mass production of ATP.

Acetyl CoA (a two-carbon molecule) enters the Krebs cycle by joining with oxaloacetate (a four-carbon molecule) in order to create the six-carbon molecule citrate.

Oxidation is the process by which a molecule loses an electron, which is caused by an oxidizing agent. Reduction is the process by which a molecule gains an electron, which is caused by a reducing agent. Remember: OIL RIG (Oxidation Is Loss of electrons, Reduction Is Gain of electrons)

 and  are the only high energy intermediates produced in cellular respiration.  is produced instead in the light reactions of photosynthesis or in the pentose phosphate pathway. However, all three of these can pass on their high energy electrons to reduce other substrates. Even though  is produced in cellular respiration, it is not a high energy intermediate.  is the most oxidized form of carbon and cannot be tapped into for further energy by standard metabolic processes.

The acetyl group from the molecule acetyl CoA (two-carbons) is added to oxaloacetate to form citrate in the beginning of the citric acid cycle. Alpha-ketoglutarate (five-carbons), succinate (four-carbons), fumarate (four-carbons), and malate (four-carbons) are all intermediates of the citric acid cycle. Acetyl-CoA can come from various metabolic pathways including glycolysis (and subsequent pyruvate dehydrogenation) and beta-oxidation of fatty acids.

The decarboxylation of pyruvate results in the production of NADH. NADH can then pass its high energy electrons through the electron transport chain, which leads to ATP production. The other high energy intermediates, except for NADPH, are produced in other stages of cellular respiration (glycolysis and Krebs cycle). Cyclic AMP is an intracellular second messenger that is involved in signal transduction and regulation of many cellular processes.

The hydrolysis of ATP releases energy, making it an exergonic reaction. Endergonic reactions require energy from a source such as the hydrolysis of ATP. ATP will spontaneously hydrolyze to form ADP and Pi, this is because the products have greater entropy, lower free energy, and thus a negative . ATP is unstable because it has three negatively-charged phosphate groups that repel one another, and because upon hydrolysis, the phosphate group(s) exhibit resonance.

Lipids yield the most amount of ATP per gram because they contain the most reduced form of carbon. Alcohols, such as ethanol, are a close second because their carbons are more reduced than they are in carbohydrates. A general guide is that lipids produce about 9kcal per gram, alcohols produce about 7kcal per gram, carbohydrates and proteins produce about 4kcal per gram and nucleic acids produce about 2kcal per gram, although they are rarely used for energy.