Glycolysis Explained with Simple Animations

The first phase of glycolysis begins when a glucose molecule approaches the cell membrane.Inside the cell, an enzyme called hexokinase catalyzes the first reaction of glycolysis.This reaction requires energy in the form of ATP - adenosine triphosphate.Hexokinase transfers a phosphate group from ATP to glucose. This process is called phosphorylation.The ATP molecule, now missing a phosphate group, becomes ADP - adenosine diphosphate.The addition of the phosphate group to glucose forms glucose-6-phosphate. This molecule is now too large to leave the cell, effectively trapping it inside.This first step of glycolysis can be summarized as: glucose plus ATP yields glucose-6-phosphate plus ADP.With glucose now phosphorylated and trapped in the cell, it's ready for the next phase of glycolysis.Continuing our journey through glycolysis, glucose-6-phosphate undergoes its first structural change.The molecule is rearranged to form fructose-6-phosphate, changing the ring structure while maintaining the phosphate group.A second ATP molecule now invests more energy by adding another phosphate group.This forms fructose-1,6-bisphosphate, now containing two phosphate groups.Now comes the critical splitting step. The six-carbon molecule breaks into two identical three-carbon compounds called PGAL, or phosphoglyceraldehyde.This splitting marks a crucial turning point in glycolysis, as these three-carbon molecules will go on to generate ATP in the next phase.Now in the payoff phase, we'll see how each PGAL molecule generates energy through multiple steps.In the first energy-harvesting step, each PGAL molecule undergoes substrate-level phosphorylation, directly producing ATP.Next, each molecule helps convert NAD+ to NADH, storing additional energy for the cell.In the final energy-harvesting step, each molecule generates another ATP through substrate-level phosphorylation.Finally, the molecules are converted to pyruvate, the end product of glycolysis.Let's examine the energy balance. While phases one and two consumed two ATP molecules, the payoff phase produces four ATP and two NADH molecules, resulting in a net gain of two ATP and two NADH per glucose molecule.The overall equation shows that one glucose molecule yields two pyruvate molecules, along with two ATP and two NADH, representing the net energy gain from glycolysis.