Question

What is the net gain of ATP molecules derived from the reactions of glycolysis?

Short answer

The net gain of ATP molecules derived from the reactions of glycolysis is 2.

Step-by-step solution

Understand Glycolysis

Glycolysis is a series of reactions that extract energy from glucose by splitting it into two molecules of pyruvate. This process occurs in the cytoplasm of the cell.

Identify ATP Consumption

In the initial steps of glycolysis, two ATP molecules are consumed to phosphorylate glucose and convert it into a form that can be split into two three-carbon molecules.

Identify ATP Production

During glycolysis, four ATP molecules are produced through substrate-level phosphorylation. These ATP molecules are generated in the later steps of the pathway.

Calculate Net Gain

The net gain of ATP is determined by subtracting the ATP consumed from the ATP produced. Therefore, the net gain is: Net ATP gain = ATP produced - ATP consumed Net ATP gain = 4 - 2

Compute the Result

Compute the net gain by performing the subtraction: Net ATP gain = 4 - 2 = 2

Key concepts

ATP consumption

During the initial stages of glycolysis, the cell uses two ATP molecules. This may seem counterintuitive since we are accustomed to thinking about energy production. Here’s why it’s necessary: The process begins with one glucose molecule, which is relatively stable. To break this down into smaller, more reactive molecules, the cell invests energy in the form of ATP. These initial two ATP molecules phosphorylate glucose, converting it into a molecule that can be split into two three-carbon compounds. This initial investment is crucial as it sets the stage for the energy payoff that follows.

ATP production

As glycolysis continues, the initial investment of ATP starts to pay off. Later in glycolysis, four ATP molecules are generated through a process known as substrate-level phosphorylation. This occurs when a phosphate group is directly transferred from a substrate to ADP, forming ATP. Each of the two three-carbon molecules created in the initial stages of glycolysis undergoes further reactions that produce two ATP molecules each, totaling four ATP. This production phase is key to understanding how cells generate energy quickly and efficiently in the cytoplasm.

substrate-level phosphorylation

One of the pivotal ways ATP is generated in glycolysis is through substrate-level phosphorylation. This method directly forms ATP by transferring a phosphate group from a high-energy substrate to ADP. It's different from oxidative phosphorylation, which occurs in the mitochondria and relies on a proton gradient. In glycolysis, substrate-level phosphorylation happens in the cytoplasm. Specifically, it occurs twice for each three-carbon molecule, resulting in the production of four ATP molecules from each glucose molecule.

glycolysis process

Glycolysis is a fundamental metabolic pathway that all living cells use to extract energy from glucose. This ten-step process occurs in the cytoplasm and does not require oxygen, making it an anaerobic process. Here’s a simplified overview:

• Starts with a glucose molecule
• Consumes 2 ATP molecules initially
• Breaks down glucose into two three-carbon pyruvate molecules
• Generates 4 ATP molecules via substrate-level phosphorylation
• Produces 2 NADH molecules

The net result is a small, but important, net gain of 2 ATP molecules per glucose molecule, which cells use for various energy-requiring activities.

cytoplasm

All the reactions of glycolysis take place in the cytoplasm of the cell. The cytoplasm is the interior fluid of the cell where many metabolic reactions occur. This location is significant because the substrates and enzymes required for glycolysis are readily available in this compartment. The cytoplasmic location also allows for rapid response to changes in energy demands, as it does not rely on the transport of molecules into the mitochondria. Therefore, glycolysis can quickly supply ATP when immediate energy is needed.