Glycolysis Transitional Reasoning Download PDF

Questions

1. 1.

   An investigator incubates a cell-free cytosolic extract with glucose, an initial pool of ATP, and all necessary cofactors except that inorganic phosphate ($\text{P}_i$) is completely omitted from the medium. The pathway successfully proceeds through the preparatory phase, converting glucose into two molecules of glyceraldehyde-3-phosphate, but halts at the subsequent oxidation step. Based on the biochemical progression of glycolysis, what is the resulting net ATP balance for each mole of glucose processed under these conditions?

   • A) A net gain of 2 moles of ATP, because substrate-level phosphorylation occurs prior to the oxidation of glyceraldehyde-3-phosphate.
   • B) A net gain of 0 moles of ATP, because the energy invested in hexose phosphorylation is recovered during triose isomerization.
   • C) A net loss of 2 moles of ATP, because the preparatory phase consumes energy while the arrest prevents all substrate-level phosphorylation steps.
   • D) A net gain of 4 moles of ATP, because cleavage of fructose-1,6-bisphosphate directly releases high-energy phosphate groups.