General view: Glucose(6-carbon sugar) being break down into:

==> 2 incomplete  pyruvates (3-carbon pyruvates)
==> 2 NADH + H+
==> 2 ATPs

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::: Glycolysis begins :::

::::::::::::::::::::::::::::::::::::::::::::::::Energy investing reactions (1 - 5):::::::::::::::::::::::::::::::::::::::::::::::::

Reaction 1:

ATP transfer a phosphate to C6H12O6 ==> glucose 6 phosphate (G6P)

Enzyme used:  Hexokinase

Reaction 2:

G6P ==> fructose 6 phosphate (F6P)

Enzyme: Phosphohexose isomerase

Reaction 3:

A 2nd ATP transfer a phosphate (ATP ==> ADP) ==> fructose 1, 6-biphosphate (FBP)

Enzyme: Phosphofructokinase

Reaction 4:

FBP ==> DAP + G3P (these 2 are isomers of each other)

Enzyme: Aldolase

Reaction 5: 

DAP ==> G3P (by rearrangement)       /       Now we have 2     G3Ps

Enzyme: Iomerase

++++++++ At this point :  2 ATP is invested

++++++++++++++++++  C6H12O6 ==> 2 G3Ps

++++++++++++++++++  No ATP is gained

++++++++++++++++++  Nothing is oxidized

::::::::::::::::::::::::::::::::::::::::::::::::Energy harvesting reactions (6-10):::::::::::::::::::::::::::::::::::::::::::::::::

Reaction 6:

2 G3Ps gain phosphate group and oxidized (very exergonic) ==> 2 NADH + H+

                                                                                                        ==> 2 BPGs

Enzyme:  Triose phosphate dehydrogenase

Reaction 7:

2 BPGs transfer phosphate group to ADP ==> ATP

                                                                         ==> 2 3PGs

Enzyme: Phosphoglycerate kinase

Reaction 8:

3PGs ==> 2PGs

Reaction 9:

2PGs lose H2O(water) ==> PEP (high energy phosphoenolpyruvates)

Enzyme: Enolase

Reaction 10:

2 PEPs transfer phosphate to ADP ==> 2 ATPs and 2 pyruvate!