What occurs during the preparatory phase of glycolysis?

During the preparatory phase of glycolysis, glucose undergoes a series of enzymatic reactions leading to its conversion into fructose 1,6-bisphosphate. Initially, glucose is phosphorylated, a process that involves the addition of a phosphate group from ATP, resulting in glucose-6-phosphate. This first phosphorylation step is crucial as it traps glucose within the cell and prepares it for subsequent transformations.

Following this initial reaction, glucose-6-phosphate is isomerized to fructose-6-phosphate and then further phosphorylated by another ATP molecule to form fructose-1,6-bisphosphate. The conversion of glucose to fructose-1,6-bisphosphate is essential for effectively splitting the six-carbon sugar into two three-carbon molecules later in the glycolysis pathway. This preparatory phase is critical for the overall energy yield from glycolysis, even though it consumes energy initially. It sets the stage for the payoff phase of glycolysis, where ATP and NADH are produced.

The other options do not accurately describe what occurs in the preparatory phase. For instance, the conversion of pyruvate occurs later, after glycolysis has processed glucose. The oxidation of NADH is also not part of this initial phase