Energy yield:

Early  in  glycolysis there are  two  ATPs  are  needed  for  the  conversion  of  glucose  to glucose   6-phosphate   through  hexokinase   and  for  the  conversion   of  fructose   6- phosphate  to fructose 1,6-bisphosphate  by PFK. Moreover,  fructose 1,6-bisphosphate  then  provides  increase  to two  three-carbon  units,  each  of that  generates  two ATPs in subsequent  steps (catalyzed  through pyruvate kinase and phosphoglycerate kinase) providing a net yield of two ATPs per original glucose molecule described in the figure. The whole reaction is:

Note that, under aerobic conditions the two NADH molecules which are synthesized  are  re-oxidized  through  the  electron  transport  chain  producing  ATP. Providing  the cytoplasmic  situation  of these  NADH  molecules,  each is re-oxidized through the glycerol 3-phosphate  shuttle and produces around two ATPs during oxidative phosphorylation  or through the malate-aspartate shuttle and produces  approximately  three ATPs during oxidative  phosphorylation.