ATP is called as a "Universal energy currency" since all the energy transactions of the cell use this molecule.
In terms of efficiency, aerobic respiration is more efficient than the anaerobic respiration which yields only two molecules of ATP. Both these modes of respiration share the initial Glycolysis step, which occurs in cytoplasm. After, the glycolysis, other reactions of the aerobic respiration, Krebs (Citric acid cycle) and oxidative phosphorylation takes place in mitochondria.
Of the four different isozymes, type IV enzyme is not amenable to feedback inhibitory mechanism and is specific to liver and pancreas. During elevated levels of blood glucose, excess amount of Glucose-6-phosphate is made for conversion to glycogen for future use in liver (Table 1).
2. The second reaction of this cascade is catalyzed by phosphoglucose isomerase leading to interconversion of glucose-6-phosphate to fructose-6-phosphate during glycolysis and gluconeogenesis (Table 1).
3. Third step in the glycolysis in another priming reaction leading to the addition of another phosphate group by an enzyme called phosphofructokinase 1. This is a unidirectional reaction committing the cells to glycolysis. A phosphatase called fructose bisphosphatase is required for the reverse reaction. A balance of enzymatic activities of phosphofructokinase and fructose bisphosphatase determines whether the reaction proceeds towards glycolysis or gluconeogenesis. This reaction is activated by AMP and also fructose 2,6-bisphosphate which is a product of the reaction catalyzed by phosphofructokinase 2. These enzymes are downregulated by glucagon at the transcriptional level. Fructose bisphosphatase is inhibited by fructose 2,6 bisphosphate (Table 1).
4. The fourth step in the process of glycolysis is the reversible cleavage of fructose 1,6 bisphosphate to form two different triose phosphates, both of which continue through glycolysis, by an enzyme termed aldolase. The different isozymes of aldolase have different catalytic functions: aldolases A and C are mainly involved in glycolysis, while aldolase B