Krebs cycle energy yield

By combining the glycolytic pathway, the Krebs cycle, and oxidative phosphorylation, the energy yield from the aerobic degradation of glucose will be... 

The a-keto acids formed by transamination of amino acids are further broken down in the citric acid (Krebs) cycle. This process yields energy, and the body s energy needs can be met with protein if sufficient carbohydrates or fats are not available. 

Most of the metabolites that serve as energy sources for aerobic organisms are broken down (catabo-lized) by various pathways to yield substrates for the central, energy-yielding citric acid cycle (also known as the tricarboxylic acid cycle or the Krebs cycle). The citric cycle is a sequence of enzymatic steps whose net reaction consists of the oxidation of acetate to carbon dioxide. 

The citric acid cycle, also known as the tricarboxylic acid cycle or the Krebs cycle, is the final oxidative pathway for carbohydrates, lipids, and amino acids. It is also a source of precursors for biosynthesis. The authors begin Chapter 17 with a detailed discussion of the reaction mechanisms of the pyruvate dehydrogenase complex, followed by a description of the reactions of the citric acid cycle. This description includes details of mechanism and stereospecificity of some of the reactions, and homologies of the enzymes to other proteins. In the following sections, they describe the stoichiometry of the pathway including the energy yield (ATP and GTP) and then describe control mechanisms. They conclude the chapter with a summary of the biosynthetic roles of the citric acid cycle and its relationship to the glyoxylate cycle found in bacteria and plants. 

Glycolysis, an anaerobic process, oxidizes glucose to yield a 3-carbon compound, pyruvic acid. Obviously, a large part of the chemical energy stored in the glucose molecule remains unavailable for cellular metabolism. Fortunately, there exists a biochemical device capable of oxidizing pyruvic acid to CO2 and water in the presence of oxygen. It is known as the Krebs cycle, the tricarboxylic acid cycle, or the citric acid cycle [69-73] (see Fig. 1-13). 

The chemical energy liberated during oxidation of the Krebs cycle substrates is captured in the electron transport chain and delivered in small packages to yield the energy-rich phosphate bond of ATP. 

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