ATP and ADP play critical roles in glycolysis, serving as energy currency for the cell. Glycolysis is the metabolic pathway that converts glucose into pyruvate.
ATP in Glycolysis
Investment Phase: In the initial steps of glycolysis, ATP is consumed. Specifically, two ATP molecules are used:
- In step 1, hexokinase uses ATP to convert glucose into glucose-6-phosphate.
- In step 3, phosphofructokinase (PFK) uses another ATP to convert fructose-6-phosphate into fructose-1,6-bisphosphate.
These steps essentially "prime" the glucose molecule for subsequent breakdown.
Yield Phase: Later in glycolysis, ATP is produced. A net of two ATP molecules are generated:
- 1,3-bisphosphoglycerate transfers a phosphate to ADP, forming ATP and 3-phosphoglycerate.
- Phosphoenolpyruvate transfers a phosphate to ADP, forming pyruvate and ATP.
Although 4 ATP molecules are produced, 2 ATP molecules are initially invested, resulting in a net gain of 2 ATP molecules per glucose molecule undergoing glycolysis.
ADP in Glycolysis
ADP is formed when ATP is used to provide energy for the initial steps of glycolysis.
ADP then accepts phosphate groups in the later steps of glycolysis to regenerate ATP.
The availability of ADP is important for regulating glycolysis. When ATP levels are high and ADP levels are low, the reactions that produce ATP are less likely to occur.