<Table> <Tr> <Th> (show) Metabolism of common monosaccharides, including glycolysis, gluconeogenesis, glycogenesis and glycogenolysis </Th> </Tr> <Tr> <Td> </Td> </Tr> </Table> <Tr> <Th> (show) Metabolism of common monosaccharides, including glycolysis, gluconeogenesis, glycogenesis and glycogenolysis </Th> </Tr> <P> While most steps in gluconeogenesis are the reverse of those found in glycolysis, three regulated and strongly endergonic reactions are replaced with more kinetically favorable reactions . Hexokinase / glucokinase, phosphofructokinase, and pyruvate kinase enzymes of glycolysis are replaced with glucose - 6 - phosphatase, fructose - 1, 6 - bisphosphatase, and PEP carboxykinase / pyruvate carboxylase . These enzymes are typically regulated by similar molecules, but with opposite results . For example, acetyl CoA and citrate activate gluconeogenesis enzymes (pyruvate carboxylase and fructose - 1, 6 - bisphosphatase, respectively), while at the same time inhibiting the glycolytic enzyme pyruvate kinase . This system of reciprocal control allow glycolysis and gluconeogenesis to inhibit each other and prevents a futile cycle of synthesizing glucose to only break it down . </P> <P> The majority of the enzymes responsible for gluconeogenesis are found in the cytosol; the exceptions are mitochondrial pyruvate carboxylase and, in animals, phosphoenolpyruvate carboxykinase . The latter exists as an isozyme located in both the mitochondrion and the cytosol . The rate of gluconeogenesis is ultimately controlled by the action of a key enzyme, fructose - 1, 6 - bisphosphatase, which is also regulated through signal transduction by cAMP and its phosphorylation . </P>

Where do glycogenesis and gluconeogenesis occur in the cell