Summary
Highlights
Glycolysis is the process where the energetic glucose molecule, a primary energy source for cells, is broken down into two pyruvate molecules. This sequence of enzyme reactions extracts energy and requires an initial energy investment, delivered by ATP, primarily sourced from mitochondria through aerobic respiration.
The first enzyme transfers a phosphate from ATP to glucose, forming glucose 6-phosphate. The second enzyme rearranges this into fructose 6-phosphate. The third enzyme uses a second ATP molecule to create fructose 1, 6-bisphosphate, preparing the six-carbon sugar for cleavage.
The fourth enzyme splits the fructose 1, 6-bisphosphate into two three-carbon sugars: glyceraldehyde 3-phosphate and dihydroxyacetone phosphate. Only glyceraldehyde 3-phosphate can continue directly in glycolysis; dihydroxyacetone phosphate must first be converted into glyceraldehyde 3-phosphate through isomerization by the fifth enzyme.
The sixth enzyme adds a second phosphate to glyceraldehyde 3-phosphate, creating 1, 3-bisphosphoglycerate. In this step, two electrons are transferred to NAD+, reducing it to NADH. At this point, the cell has consumed two ATP molecules and is now ready to generate energy.
The seventh enzyme transfers a phosphate from 1, 3-bisphosphoglycerate to ADP, forming ATP. The eighth enzyme rearranges the phosphate group. The ninth enzyme catalyzes dehydration, increasing the potential energy. Finally, the tenth enzyme transfers the remaining phosphate to ADP, producing ATP and the three-carbon sugar, pyruvate. Glycolysis results in a net gain of two ATP and two NADH per glucose molecule.