Glycolysis Glucose (C 6 ) is split to make 2 Pyruvates (C 3 ) –1 st : ATP energy used to phosphorylate glucose (stored energy) –2 nd : phosphorylated glucose broken down into two C 3 sugar phosphates –3 rd : the sugar phosphates are oxidized to yield electrons and H + ions which are donated to 2 NAD + → 2 NADH (stored electron and hydrogen for the Electron Transport Chain) –4 th : The energy from oxidation is used to make 4 ATP molecules (net 2 ATP) This is substrate level phosphorylation because an enzyme transfers phosphate to ADP making ATP Glycolysis produces very little ATP energy, most energy is still stored in Pyruvate molecules.