Aerobic vs Anaerobic Glycolysis: Difference and Comparison

Glycolysis is the metabolic pathway that helps produce energy from the food we take in, especially carbs. The term glycolysis means the lysis of glucose, i.e., the breakdown of glucose.

The 6 carbon-containing glucose molecules we consume are broken down into pyruvates (3 carbon-containing molecules) by glycolysis, a ten-step pathway.

Glycolysis occurs in the cytoplasm and leads to the formation of two molecules of pyruvate from one glucose molecule. The classification of glycolysis into aerobic or anaerobic depends on the fate of this pyruvate formed.

Suppose this pyruvate is broken down further into simpler molecules in the presence of oxygen. In that case, glycolysis is termed aerobic glycolysis. Still, if the pyruvate is converted into other carbon-containing compounds without oxygen, glycolysis is termed anaerobic.

Key Takeaways

1. Aerobic glycolysis breaks down glucose with oxygen to produce energy, while anaerobic glycolysis breaks down glucose without oxygen.
2. Aerobic glycolysis produces more ATP, the primary energy source for cells, than anaerobic glycolysis.
3. Aerobic glycolysis occurs in the mitochondria of cells, while anaerobic glycolysis occurs in the cytoplasm.

Aerobic Glycolysis vs Anaerobic Glycolysis

The difference between aerobic glycolysis and anaerobic glycolysis is that aerobic glycolysis proceeds in the presence of oxygen and occurs in eukaryotic cells. In contrast, anaerobic glycolysis proceeds without oxygen and occurs in eukaryotic and prokaryotic cells.

Aerobic glycolysis continues in the mitochondria through Kreb’s Cycle or TCA and ETS, forming the final products, CO2 and water. In contrast, anaerobic glycolysis continues in the cytoplasm, forming the final product, ethanol or lactic acid, depending on the type of fermentation.

Comparison Table

Parameters of Comparison	Aerobic Glycolysis	Anaerobic Glycolysis
Oxygen involvement	Aerobic glycolysis proceeds in the presence of oxygen.	Anaerobic glycolysis proceeds in the absence of oxygen.
Occurs in	Aerobic glycolysis occurs only in eukaryotic cells.	Anaerobic glycolysis can take place in eukaryotic as well as prokaryotic cells.
Continues through	Aerobic glycolysis continues through the Kreb or tricarboxylic acid cycles and then the Electron Transport System.	Anaerobic glycolysis continues through either Lactic Acid Fermentation, as in muscle cells of humans, or Ethanol Fermentation, as in unicellular eukaryotes like yeasts and prokaryotes like bacteria.
Continues inside	Aerobic glycolysis continues inside mitochondria present in eukaryotes.	Anaerobic glycolysis continues inside the cytoplasm.
End products	Aerobic glycolysis leads to the Kreb cycle and ETS; the final products formed are CO2 and water.	Anaerobic glycolysis leads to ethanol fermentation or lactic acid fermentation; thus, the final products are ethanol or lactic acid.

What is Aerobic Glycolysis?

Aerobic glycolysis is a part of aerobic respiration that occurs in eukaryotes in the presence of oxygen and produces 2 GTP, 6 NADH, and 2 FADH_2, which undergo oxidative phosphorylation.

Aerobic glycolysis proceeds through the Krebs cycle, the tricarboxylic acid cycle, and the electron transport system within mitochondria. Aerobic glycolysis takes place exclusively in eukaryotic cells.

In aerobic glycolysis, one glucose molecule is broken down into two pyruvate molecules.

The pyruvate molecules are further converted into acetyl coenzyme A, passed on to the mitochondria to proceed with the Krebs or the TCA cycle, followed by Electron Transport System, finally giving rise to the end products CO₂ and water. 

What is Anaerobic Glycolysis?

Anaerobic glycolysis is a part of anaerobic respiration that occurs in the absence of oxygen and produces only 4 NADH molecules that are regenerated through substrate-level phosphorylation.

Anaerobic glycolysis can take place in eukaryotic and prokaryotic cells, and it takes place in the cytosol or the cytoplasm.

Anaerobic glycolysis proceeds through either of the two fermentation processes: lactic acid fermentation and alcoholic fermentation. These take place in the cytoplasm of prokaryotic or eukaryotic cells.

1. Lactic Acid Fermentation

Some cells of the eukaryotes, like the muscle cells, produce lactic acid from the 3-carbon molecule pyruvate produced at the end of glycolysis. The reducing agent for this process is NADH + H⁺, and the enzyme involved is lactate dehydrogenase.

Lactic acid fermentation occurs in muscle cells during strenuous workouts when enough oxygen cannot be provided to the muscle cells. It helps in muscle building.

2. Ethanol Fermentation 

In ethanol fermentation, pyruvate is converted into CO₂ and ethanol under anaerobic conditions. Ethanol fermentation takes place in unicellular eukaryotes like yeasts and many prokaryotes.

The enzymes involved in this process are pyruvic acid carboxylate and alcohol dehydrogenase, which catalyst these reactions. 

In both lactic acid fermentation and alcoholic fermentation, very little energy is released. Both are dangerous reactions, as we can see that either acid or alcohol is produced as the end product of the processes.

Main Differences Between Aerobic Glycolysis and Anaerobic Glycolysis

1. Aerobic glycolysis proceeds in the presence of oxygen, while anaerobic glycolysis proceeds in the absence of oxygen.
2. Aerobic glycolysis occurs in eukaryotic cells, while anaerobic glycolysis occurs in eukaryotic and prokaryotic cells. 
3. Aerobic glycolysis proceeds in mitochondria through the Krebs cycle, while anaerobic glycolysis proceeds in the cytoplasm through lactic acid fermentation or ethanol fermentation.
4. Aerobic glycolysis finally leads to the formation of CO₂ and water, while anaerobic glycolysis finally leads to the formation of ethanol or lactic acid.
5. The pyruvate formed is converted to acetyl coenzyme A in aerobic glycolysis, while it is converted to lactate or acetaldehyde in anaerobic glycolysis.

References

1. https://shapeamerica.tandfonline.com/doi/pdf/10.1080/02701367.1980.10609285
2. https://www.annualreviews.org/doi/abs/10.1146/annurev-cellbio-092910-154237
3. https://europepmc.org/article/nbk/nbk546695