Beginning a study of metabolic pathways with the reactions of glucose is more
than just a tradition—it reflects the central position of glucose metabolism
in virtually all cells. In this chapter we will use the major glucose pathways
(glycolysis, glycogen synthesis and degradation, gluconeogenesis, and the pentose
phosphate pathway) to illustrate the first of several general themes of metabolism.
Specifically, we will show that pathways are series of chemical reactions in which
specific enzymes catalyze the transformation of specific metabolic intermediates.
some of these molecular transformations are metabolically irreversible and serve
as regulatory points for the entire pathway.