How many ATP molecules are used and produced per molecule of glucose during glycolysis? a. The first half of glycolysis uses 2 ATPs, and the second half of glycolysis produces 4 ATPs. b. The first half of glycolysis produces 2 ATPs, and the second half of glycolysis uses 4 ATPs. c. The first half of glycolysis uses 4 ATPs, and the second half of glycolysis produces 2 ATPs. d. The first half of glycolysis produces 4 ATPS, and the second half of glycolysis uses 2 ATP
The Correct Answer and Explanation is:
Correct answer: a. The first half of glycolysis uses 2 ATPs, and the second half of glycolysis produces 4 ATPs.
Explanation:
Glycolysis is the first stage of cellular respiration, where one molecule of glucose (a six-carbon sugar) is broken down into two molecules of pyruvate (each with three carbon atoms). This process takes place in the cytoplasm of cells and does not require oxygen. It involves a series of ten enzymatic steps that can be grouped into two main phases: the energy investment phase and the energy payoff phase.
In the energy investment phase (first half of glycolysis), the cell spends energy to prepare glucose for splitting. Specifically, two molecules of ATP are used to phosphorylate glucose and its intermediates. These phosphorylation steps are crucial because they help trap glucose in the cell and activate it for further reactions.
In the energy payoff phase (second half of glycolysis), four ATP molecules are produced by substrate-level phosphorylation. This occurs as the three-carbon intermediates are converted into pyruvate. In addition to ATP, this phase also generates two molecules of NADH, which can be used later in the electron transport chain to produce even more ATP under aerobic conditions.
Therefore, although 4 ATP molecules are produced during glycolysis, 2 ATP molecules are used in the earlier steps. This results in a net gain of 2 ATP molecules per glucose molecule.
To summarize:
- ATP used: 2 (energy investment phase)
- ATP produced: 4 (energy payoff phase)
- Net ATP gain: 2
This balanced energy exchange highlights the importance of glycolysis as a rapid but limited source of energy, especially in anaerobic conditions where further ATP production is not possible through oxidative phosphorylation.
