Number of ATP molecules and NADH formed in each cycle of glycolysis?
**Core Concept**
Glycolysis is a metabolic pathway that converts glucose into pyruvate, generating a small amount of ATP and NADH in the process. This pathway is crucial for energy production in the cell, especially in the absence of oxygen.
**Why the Correct Answer is Right**
In each cycle of glycolysis, two ATP molecules are produced (one from substrate-level phosphorylation and the other from the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate). Additionally, two NADH molecules are formed as a result of the reduction of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate. This process is essential for the subsequent steps of cellular respiration, including the citric acid cycle and oxidative phosphorylation.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because glycolysis produces a net gain of 2 ATP molecules and 2 NADH molecules, not 4 of each.
**Option B:** This option is incorrect because glycolysis does not produce 1 ATP molecule and 1 NADH molecule per cycle; rather, it produces a net gain of 2 ATP molecules and 2 NADH molecules.
**Option C:** This option is incorrect because glycolysis produces 2 ATP molecules and 2 NADH molecules, not 3 of each.
**Clinical Pearl / High-Yield Fact**
Glycolysis is a key metabolic pathway that occurs in the cytosol of cells, producing a small amount of ATP and NADH. Understanding the steps and products of glycolysis is essential for appreciating the broader context of cellular respiration and energy production in the cell.
**Correct Answer: D. 2 ATP and 2 NADH.**