The production of ATP through glycolysis is fundamentally the same under both aerobic and anaerobic conditions, but the subsequent processes differ significantly, leading to different overall ATP yields. Here's a comparison of glycolysis under these two conditions in animals:
Glycolysis Overview:
- Glycolysis occurs in the cytoplasm and involves the breakdown of glucose (a six-carbon sugar) into two molecules of pyruvate (a three-carbon compound), producing a net gain of 2 ATP molecules and 2 NADH molecules per glucose molecule.
Glycolysis Under Aerobic Conditions:
- Pathway: Glycolysis occurs as usual, producing 2 ATP and 2 NADH from 1 glucose molecule.
- Oxygen Availability: Adequate oxygen is present, allowing further processing of pyruvate.
- Products:
- Pyruvate: Enter the mitochondria where it is converted into acetyl-CoA in the presence of oxygen.
- NADH: The NADH produced in glycolysis is oxidized in the electron transport chain (ETC).
- ATP Yield:
- The NADH generated in glycolysis can lead to the production of approximately 2.5 ATP (via oxidative phosphorylation) per NADH when it enters the ETC.
- Total ATP yield:
- Glycolysis: 2 ATP
- From NADH (2 NADH x 2.5 ATP): 5 ATP
- Total ≈ 7 ATP per glucose under aerobic conditions.
Glycolysis Under Anaerobic Conditions:
- Pathway: Glycolysis also occurs, producing 2 ATP and 2 NADH from 1 glucose molecule.
- Oxygen Availability: In the absence of oxygen, pyruvate does not enter the mitochondria and cannot be fully oxidized.
- Products:
- Pyruvate: Amasses in the cytoplasm and is converted into lactate (lactic acid) through lactic acid fermentation.
- NADH: NADH cannot be oxidized through the ETC due to the lack of oxygen, so it must be reoxidized in the cytoplasm.
- ATP Yield:
- The net ATP yield from glycolysis remains at 2 ATP.
- NADH is converted back to NAD+ during the conversion of pyruvate to lactate, but no additional ATP is generated via the electron transport chain.
- Total ATP yield: 2 ATP per glucose under anaerobic conditions.
Summary Comparison:
-
Aerobic Glycolysis:
- Net ATP: 7 ATP (2 ATP from glycolysis + ~5 ATP from NADH)
- End products: Pyruvate converted to acetyl-CoA, enters the Krebs cycle.
-
Anaerobic Glycolysis:
- Net ATP: 2 ATP (from glycolysis only)
- End products: Pyruvate converted to lactate, which may accumulate in muscles leading to fatigue.
Key Differences:
- Oxygen Requirement: Aerobic conditions require oxygen, while anaerobic does not.
- End Products: Aerobic metabolism leads to complete oxidation of glucose, while anaerobic results in lactate.
- ATP Yield: Aerobic conditions yield significantly more ATP due to further oxidation via the electron transport chain.
Understanding these differences is crucial for comprehending cellular energy production, particularly in muscle physiology during exercise when oxygen availability can fluctuate.