First, Glucose (sugar molecule) gets converted into Glucose-6-phosphate (G6P) by an enzyme called hexokinase (in liver, the enzyme is called glucokinase), a highly regulated enzyme. Afterwards, G6P gets isomerized into Fructose 6 Phosphate (F6P) by an enzyme called phosphofructokinase (PFK1), which is another highly regulated enzyme. F6P then gets cut in half into two products: DHAP and G3P by an enzyme called aldolase. DHAP then transformes into G3P. So now we have 2 G3P. The 2 G3P both become phosphorylated to become 1,3 bisphophogylcerate (1,3 BPG) by an enzyme called G3P dehydrogenase, which uses 1 inorganic phosphate per G3P and produces 1 NADH per G3P. Now we have 2 1,3BPG. This is where oxidative phosphorylation occurs, where 1 phosphate gets plucked off 1,3 BPG by phosphoglycerate kinase, yielding 3PG. This yields 1 ATP per 1,3BPG. Now, our bodies then change the 3PG to 2PG by phophoglyceromutase. 2PG then gets reduced to phosphoenolpyruvate (PEP) by enolase. Finally, the PEP becomes pyruvate by the third highly regulated enzyme, pyruvate kinase. The conversion of PEP to pyruvate also yields ATP.
The 3 highly regulated enzymes in this reaction are:
hexokinase (glucokinase in liver)
These enzymes not only facilitate irreversible reactions but are also key sites for control of the glycolytic pathway.
It boggles my mind that an act as simple as eating a candy bar can elicit so many metabolic reactions without us consciously knowing.