The main difference between aerobic and anaerobic glycolysis is that aerobic glycolysis occurs in the presence of oxygen, whereas anaerobic glycolysis occurs in the absence of oxygen. Furthermore, aerobic glycolysis leads to a significantly efficient ATP production pathway, which proceeds through Krebs cycle and oxidative phosphorylation while anaerobic glycolysis leads to a less efficient ATP production pathway, which proceeds either through ethanol fermentation or lactic acid fermentation.
In brief, aerobic and anaerobic glycolysis are two initial pathways which lead to completely different types of cellular respiration pathways. However, both types of glycolysis start from glucose and end up with two pyruvate molecules. Also, 2 ATP molecules and 2 NADH molecules are produced in each type of glycolysis.
Key Areas Covered
1. What is Glycolysis
– Definition, Process, Importance
2. What is Aerobic Glycolysis
– Definition, Significance
3. What is Anaerobic Glycolysis
– Definition, Significance
4. What are the Similarities Between Aerobic and Anaerobic Glycolysis
– Outline of Common Features
5. What is the Difference Between Aerobic and Anaerobic Glycolysis
– Comparison of Key Differences
Key Terms
Aerobic Glycolysis, Aerobic Respiration, Anaerobic Glycolysis, Anaerobic Respiration, Glycolysis
What is Glycolysis
Glycolysis is the first step of cellular respiration in all living organisms. Generally, there are two types of cellular respiration that occur among living organisms. They are aerobic and anaerobic respiration. Glycolysis occurs in both types of respiration. It occurs in the cytosol, and is responsible for the breakdown of glucose into two molecules of pyruvate. Initially, a phosphate group is added to the glucose molecule by the enzyme hexokinase, producing glucose 6-phosphate. Then, glucose-6-phosphate undergoes isomerization, forming fructose-6-phosphate. After that, fructose 6-phosphate is converted to fructose 1, 6-bisphosphate, which further splits into dihydroxyacetone and glyceraldehyde by the action of the enzyme aldose.
Figure 1: Glycolysis
Furthermore, both dihydroxyacetone and glyceraldehyde are readily converted into dihydroxyacetone phosphate and glyceraldehyde 3-phosphate, which is then oxidized to 1, 3-bisphosphoglycerate. Here, the removing phosphate group is incorporated into NAD+, producing NADH by the action of glyceraldehyde 3-phosphate dehydrogenase. Also, one phosphate group from the 1, 3-bisphosphoglycerate is transferred to ADP to produce an ATP. Then, this produces a 3-phosphoglycerate molecule whose phosphate group is transferred into the second carbon position of the same molecule to form a 2-phosphoglycerate molecule. In addition to this, the removal of a water molecule from the 2-phosphoglycerate produces the phosphoenolpyruvate (PEP). Finally, the transfer of the phosphate group of PEP to an ADP molecule produces a pyruvate molecule. Most importantly, the overall reactions of the glycolysis produce two pyruvate molecules, two NADH molecules, two ATP molecules, and two water molecules.
What is Aerobic Glycolysis
Aerobic glycolysis is the type of glycolysis occurring in the presence of oxygen. Therefore, it leads to aerobic respiration, which is a type of cellular respiration taking place in the presence of oxygen. The two subsequent steps of aerobic respiration are the Krebs cycle and the oxidative phosphorylation. Pyruvate, which is the end product of the glycolysis, transforms into the matrix of mitochondria, forming acetyl-CoA from pyruvate by eliminating carbon dioxide in a process called oxidative decarboxylation. Basically, acetyl-CoA enters the Krebs cycle, which completely oxidizes a single pyruvate molecule into 3 carbon dioxide molecules along with a GTP, 3 NADH, and 1 FADH2 molecule. Furthermore, NADH and FADH2 molecules undergo oxidative phosphorylation to produce ATPs. The total yield of ATP in aerobic respiration is 30-32.
Figure 2: Aerobic Respiration
Sometimes, aerobic glycolysis also refers to a condition called the Warburg Effect in which glucose is converted to lactate in the presence of oxygen. Here, when oxygen is in short supply or when cells are undergoing aerobic glycolysis, NADH reduces pyruvate to lactate instead of re-oxidized in mitochondria by oxidative phosphorylation. Regrettably, this reduces the total yield of ATP in aerobic respiration. However, the clinical significance of aerobic glycolysis occurs within cancer stem cells in a tumour. Hence, extensive aerobic glycolysis has been indicative of aggressive cancer.
What is Anaerobic Glycolysis
Anaerobic glycolysis is the type of glycolysis occurring in the absence of oxygen. Thus, it leads to anaerobic respiration. Basically, there are two types of anaerobic respiration: ethanol fermentation and lactic acid fermentation. Ethanol fermentation mainly occurs in yeast and lactic acid fermentation occurs in mammals. In addition, in bacteria, lactate is replaced by different substances such as propionate. Furthermore, in ethanol fermentation, pyruvate, which is the end product of glycolysis, is converted into acetaldehyde by pyruvate decarboxylase, releasing carbon dioxide. Then, the action of alcohol dehydrogenase converts acetaldehyde into ethanol. However, in the absence of sufficient amounts of oxygen in muscle cells, lactic acid fermentation takes place by reducing pyruvate into lactate.
Figure 3: Ethanol Fermentation
Moreover, there is another type of anaerobic respiration, occurring in prokaryotes, and the final electron acceptor is sulfate or nitrate at the end of the electron transport chain. Also, in methanogens, the final electron acceptor is carbon dioxide. However, the main feature of anaerobic respiration, as well as fermentation, is the less efficient production of ATP. Generally, the total ATP production is 2 in the type of cellular respirations staring from anaerobic glycolysis. Essentially, these 2 ATP molecules are from the glycolysis.
Similarities Between Aerobic and Anaerobic Glycolysis
- Aerobic and anaerobic glycolysis are the two types of glycolytic pathways found in different cellular respiration pathways.
- Especially, both are the initial steps of each type of cellular respiration.
- They occur in the cytosol.
- Usually, they start with glucose and convert it into two pyruvate molecules while producing 2 ATP and 2 NADH molecules.
Difference Between Aerobic and Anaerobic Glycolysis
Definition
Aerobic glycolysis refers to the type of glycolysis that occurs in the presence of oxygen while anaerobic glycolysis refers to the type of glycolysis which occurs in the absence of oxygen.
Occurrence
In general, aerobic glycolysis occurs inside eukaryotic cells while anaerobic glycolysis occurs in both prokaryotic and eukaryotic cells.
Leads to
Moreover, aerobic glycolysis proceeds through the Krebs cycle and oxidative phosphorylation while anaerobic glycolysis proceeds either through ethanol fermentation or lactic acid fermentation.
Involvement of Mitochondria
Aerobic glycolysis further proceeds inside the mitochondria while anaerobic glycolysis further proceeds in the cytosol.
Fate of Pyruvate
Furthermore, aerobic glycolysis is responsible for oxidizing pyruvate into acetyl-CoA while anaerobic glycolysis is responsible for reducing pyruvate either into lactate in the lactic acid fermentation or acetaldehyde in the ethanol fermentation.
End Products
The end products of aerobic glycolysis are carbon dioxide and water while the end products of anaerobic glycolysis can mainly be lactic acid or ethanol.
Cofactors
Collectively, aerobic respiration produces 2 GTPs, 6 NADH and 2 FADH2, which undergo oxidative phosphorylation, while anaerobic respiration produces only 4 NADH molecules, which regenerate through substrate-level phosphorylation.
Production of ATP from Cofactors
Cofactors in aerobic respiration involve the production of ATP while the cofactors in the anaerobic respiration do not involve the production of ATP.
ATP Production
Besides, aerobic glycolysis leads to a significantly efficient ATP production pathway, which produces 32 ATPs per glucose molecule, while anaerobic glycolysis leads to a less efficient ATP production pathway, which produces 2 ATPs per glucose molecule.
Conclusion
Aerobic glycolysis is the type of glycolysis occurring in the presence of oxygen. Therefore, it leads to aerobic respiration, which occurs in eukaryotic cells. Hence, aerobic glycolysis leads to significantly efficient production of ATPs. In comparison, anaerobic glycolysis is the type of glycolysis, occurring in the absence of oxygen. Thus, it leads to either lactic acid fermentation or ethanol fermentation with very low production of ATPs. Therefore, the main difference between aerobic and anaerobic glycolysis is their requirement of oxygen and allowance to produce ATPs.
References:
1. Naifeh J, Varacallo M. Biochemistry, Aerobic Glycolysis. [Updated 2018 Dec 20]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2019 Jan-. Available Here.
2. “Anaerobic Glycolysis.” Anaerobic Glycolysis – an Overview | ScienceDirect Topics, Available Here.
3. “Anaerobic Glycolysis.” Wikipedia, Wikimedia Foundation, 28 Nov. 2019, Available Here.
Image Courtesy:
1. “Glycolysis including irreversible steps” By Lkate2014 – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “CellRespiration” By RegisFrey – Own work (CC BY-SA 3.0) via Commons Wikimedia
3. “Ethanol fermentation” By David B. Carmack Jr. – Own work (CC BY-SA 3.0) via Commons Wikimedia
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