glycolysis - stage 1 

• 10 reaction sequence converting glucose to 2 3-carbon molecules of pyruvate
• glucose + 2ADP + 2P + 2NAD+ >> 2 pyruvate + 2ATP + 2NADH + 2H+ + 2H2O
• can be performed by all organisms (doesn't require oxygen or special organelles)
• metabolism evolves by adding reactions to each other, so glycolysis was never replaced

priming - 1st half of glycolysis; makes 2 3-carbon glyceraldehyde 3-phosphates from glucose  

• 5 reactions
• step A - glucose priming
  • 3 reactions changing glucose into a compound that can be readily cleaved into 3-carbon phosphorylated molecules
  • 2 of the reactions require use of ATP
• step B - cleavage/rearrangement
  • 2 reactions break up 6-carbon molecule into 2 3-carbon molecules
  • 1st of 2 reactions forms G3P and another molecule that turns into G3P through the 2nd reaction

substrate-level phosphorylation - 2nd half of glycolysis; makes pyruvate from G3P 

• 5 reactions
• step C - oxidation
  • 2 electrons, 1 proton transferred from G3P to NAD+ to make NADH
• step D - ATP generation
  • 4 reactions convert G3P to pyruvate, generating 2 ATP
• in total, 4 ATP per glucose molecule produced
• 2 ATP used in beginning, so glycolysis has net ATP gain of 2
• harvests 24 kcal/mol of glucose, about 3.5% of chemical energy in glucose

regeneration of NADH - only a small amount of NAD+ exists in cells 

• necessary that the H on NADH be transferred somewhere else
• aerobic respiration - uses oxygen as electron acceptor (takes the H to become H2O); oxidizes pyruvate to acetyl-CoA
• fermentation - uses organic molecule (like acetaldehyde) in place of oxygen; reduces all or part of pyruvate