Question

How many ATPs can be produced from one molecule of glucose anaerobically? Aerobically?

Short answer

2 ATPs anaerobically, approximately 38 ATPs aerobically.

Step-by-step solution

Understand Glycolysis

Glycolysis is the process where one molecule of glucose is broken down into two molecules of pyruvate. During glycolysis, a net gain of 2 ATP molecules is produced.

ATP Production Anaerobically

Anaerobic glycolysis refers to the breakdown of glucose in the absence of oxygen. In this process, only glycolysis takes place, which results in a net gain of 2 ATP molecules per glucose molecule.

ATP Production Aerobically

In the presence of oxygen, glucose metabolism involves glycolysis, the citric acid cycle, and the electron transport chain. Glycolysis produces 2 ATP, the citric acid cycle produces 2 ATP, and the electron transport chain produces about 34 ATP. The total ATP produced aerobically per glucose molecule is approximately 38 ATP.

Key concepts

Glycolysis

Glycolysis is the first step in both anaerobic and aerobic respiration. It occurs in the cytoplasm of the cell and does not require oxygen. During glycolysis, one molecule of glucose is broken down into two molecules of pyruvate. This process generates a net gain of 2 ATP molecules and 2 molecules of NADH (nicotinamide adenine dinucleotide).

• The glucose molecule (C₆H₁₂O₆) is converted to 2 molecules of pyruvate (C₃H₄O₃).
• Each molecule of glucose converted results in a net gain of 2 ATP and 2 NADH.
• Two molecules of ATP are consumed during the initial steps of glycolysis, but 4 ATP are produced in the latter steps, yielding a net production of 2 ATP.

Understanding glycolysis is critical because it is a fundamental pathway that leads to further stages of metabolism, whether oxygen is available or not.

Anaerobic Respiration

Anaerobic respiration happens when oxygen is not available. In this case, only glycolysis occurs, and the pyruvate produced is typically converted into lactate (in animals) or ethanol and carbon dioxide (in yeast).

• Since it only involves glycolysis, anaerobic respiration yields a net gain of 2 ATP molecules per glucose molecule.
• The conversion of pyruvate to lactate or ethanol helps regenerate NAD⁺, which is essential for glycolysis to continue.
• This process is less efficient than aerobic respiration because it does not produce additional ATP from the electron transport chain or the citric acid cycle.

Even though anaerobic respiration produces much less ATP than aerobic respiration, it is crucial for cells to survive in low-oxygen environments.

Aerobic Respiration

Aerobic respiration requires oxygen and involves multiple steps: glycolysis, the citric acid cycle, and the electron transport chain.

• Glycolysis, as mentioned, yields a net gain of 2 ATP.
• The pyruvate from glycolysis then enters the mitochondria, where it is used in the citric acid cycle (also known as the Krebs cycle). This cycle produces 2 more ATP per glucose molecule, along with additional NADH and FADH₂.
• The NADH and FADH₂ produced during glycolysis and the citric acid cycle donate electrons to the electron transport chain, located in the inner mitochondrial membrane.
• The electron transport chain generates about 34 ATP through oxidative phosphorylation, making it the most ATP-productive phase.

In total, aerobic respiration produces approximately 38 ATP per glucose molecule. This makes it much more efficient in energy production compared to anaerobic respiration.