Citric acid cycle description

Q ttflif Identify the steps in the citric acid cycle that fit the following descriptions. 

A scientific and personal biography of Krebs by an eminent historian of science, with a thorough description of the work that revealed the urea and citric acid cycles. 

How the Citric Acid Cycle Was Determined The detailed biochemistry of the citric acid cycle was determined by several researchers over a period of decades. In a 1937 article, Krebs and Johnson summarized their work and the work of others in the first published description of this pathway. 

This reaction is important because it provides oxaloacetate for the citric acid cycle when the supplies have run low because of the demands of biosynthesis. It is also the enzyme that catalyzes the first step in gluconeogenesis, the pathway that provides the body with needed glucose in times of starvation or periods of exercise that deplete glycogen stores. But somehow these descriptions don t fill us with a sense of the importance of this enzyme and its jobs. It is not until we investigate a case study of a child born with pyruvate carboxylase deficiency that we see the full impact of this enzyme. 

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. 

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