Gluconeogenesis pathway steps

Biomolecules are synthesized as well as degraded, but the pathways for anabolism and catabolism are not the exact reverse of one another. Fatty acids are biosynthesized from acetate by an 8-step pathway, and carbohydrates are made from pyruvate by the 11-step gluconeogenesis pathway. 

The gluconeogenesis pathway for biosynthesis of glucose frorn pyruvate. The individual steps are explained in more detail in the text. 

Again, this occurs only under conditions of high ATP and NADH concentrations, which also drive the next several reversible steps to produce fructose-1,6-bisphosphate. The formation of this compound from fructose-6-P04 through glycolysis is irreversible therefore, in the second bypass reaction, the gluconeogenesis pathway utilizes a new enzyme, fructose diphosphatase, to irre-... 

FIGURE 22.11 A comparison of glycolysis and gluconeogenesis pathways. The pathways differ at the three steps indicated by red reaction arrows. 

However, carbon dioxide is incorporated into the organic substrate and converted into a carboxylate group in the six-carbon sugar derivative. The hydrolysis of the carboxylate (Step 4) affords two molecules of 3-phosphoglycerate, which are incorporated into the gluconeogenesis pathway of glucose synthesis. 

The gluconeogenesis pathway for the biosynthesis of giucose from pyruvate, individuai steps are expiained in the text. 

The complete route of gluconeogenesis is shown in Figure 23.1, side by side with the glycolytic pathway. Gluconeogenesis employs three different reactions, catalyzed by three different enzymes, for the three steps of glycolysis that are... 

Phosphoenolpyruvate carboxykinase (PEPCK) catalyzes a critical reaction in gluconeogenesis, which under many conditions is the rate-limiting step in the pathway. A cAlVfP response element (CRE) and a glucocorticoid response element (GRE) are each located upstream from the transcription start site. 

Propionyl CoA is converted to sucdnyl CoA, a dtric add cyde intermediate, in the two-step propionic add pathway. Because this extra sucdnyl CoA can form malate and enter the cytoplasm and gluconeogenesis, odd-carbon fatty adds represent an exception to the rule that fatty... 

The pathway for gluconeogenesis is shown in Figures 6.23 and 6.24. Some of the reactions are catalysed by the glycolytic enzymes i.e. they are the near-equilibrium. The non-equilibrium reactions of glycolysis are those catalysed by hexokinase (or glucokinase, in the liver), phosphofructokinase and pyruvate kinase and, in order to reverse these steps, separate and distinct non-equilibrium reactions are required in the gluconeogenic pathway. These reactions are ... 

The steps of the signaling pathway also distribute the signal to several response pathways in the cell (eg, glucagon action to increase glucose production by the liver is mediated by increases in both gluconeogenesis and glycogenolysis). 

FIGURE 15-15 Glycolysis and gluconeogenesis. Opposing pathways of glycolysis (pink) and gluconeogenesis (blue) in rat liver. Three steps are catalyzed by different enzymes in gluconeogenesis... 

Because the carbon atoms of acetate molecules that enter the citric acid cycle appear eight steps later in oxaloacetate, it might seem that this pathway could generate oxaloacetate from acetate and thus generate phosphoenolpyruvate for gluconeogenesis. However, as an examination of the stoichiometry of the citric acid cycle shows, there is no net conversion of acetate to ox-... 

The relationship of the pentose-phosphate pathway to glycolysis is shown in Figure 20-11. The steps involved in the pentose shunt are readily reversible, but there are several steps in glycolysis that are not. These are the phosphorylation steps (see Figure 20-9). Yet, there has to be a return route from pyruvate to glucose. This route is called gluconeogenesis and, in animals, takes place in... 

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