Final answer:
In glycolysis, there is a net gain of two ATP molecules per glucose molecule broken down. This net gain can vary under different conditions, and the NADH produced can also contribute to ATP production if used in the electron transport chain.
Step-by-step explanation:
Net Gain of ATP in Glycolysis
The process of glycolysis begins with a glucose molecule and results in the production of two pyruvate molecules. During this metabolic pathway, there is an initial investment of two ATP molecules; however, four ATPs are subsequently produced in Stage 2 of glycolysis. This leads to a net gain of two ATP molecules that the cell can use for energy.
It's important to note that two molecules of NADH are also generated in glycolysis, which can be further utilized in the electron transport chain to produce more ATP under aerobic conditions. However, the actual yield of ATP can differ based on the type of cell and the shuttle system used to transport NADH into the mitochondria. For instance, in muscle cells, the glycerol phosphate shuttle is employed, using the two ATP produced in glycolysis to transport the NADH, leading to a net zero ATP gain specifically from glycolysis. Conversely, with the malate-aspartate shuttle, which is more efficient, the net gain of ATP can reach higher values when NADH is oxidized in the electron transport chain.
When considering anaerobic conditions, such as in muscle cells during intense activity, ATP production is solely from glycolysis, yielding a net gain of two ATP per glucose molecule. This is because the pyruvate is converted to lactate, and the NADH produced in glycolysis is used to convert pyruvate to lactate, rather than being shuttled to the mitochondria for further ATP production.