What is the Difference Between Cytosolic and Chloroplastic Glycolysis

The main difference between cytosolic and chloroplastic glycolysis is that cytosolic glycolysis is a linear pathway that occurs continuously in the cytosol, whereas chloroplastic glycolysis occurs in glucose at higher concentrations inside the chloroplasts.

Cytosolic and chloroplastic glycolysis are two processes that break down glucose into two pyruvate molecules. Both processes use the energy of glucose for the production of ATP.

Key Areas Covered

1. What is Cytosolic Glycolysis
     – Definition, Structure, Function
2. What is Chloroplastic Glycolysis
     – Definition, Structure, Function
3. Similarities Between Cytosolic and Chloroplastic Glycolysis
     – Outline of Common Features
4. Difference Between Cytosolic and Chloroplastic Glycolysis
     – Comparison of Key Differences

Key Terms

Chloroplastic Glycolysis, Cytosolic Glycolysis

What is Cytosolic Glycolysis

Cytosolic glycolysis is the process of converting glucose into two pyruvate molecules. It occurs inside the cytosol. It is the first step of cellular respiration in all living organisms. That means glycolysis occurs in both aerobic and anaerobic respiration. Glycolysis, occurring in the cytoplasm, is responsible for the breakdown of glucose into two molecules of pyruvate. The enzyme hexokinase adds a phosphate group to the glucose molecule and thus producing glucose 6-phosphate. The glucose-6-phosphate is then isomerized to fructose-6-phosphate. Meanwhile, the fructose 6-phosphate is converted to fructose 1, 6-bisphosphate.

Figure 1: Glycolysis

Furthermore, fructose 1, 6-bisphosphate is split into dihydroxyacetone and glyceraldehyde by the action of the enzyme aldose. Both dihydroxyacetone and glyceraldehyde are readily converted into dihydroxyacetone phosphate and glyceraldehyde 3-phosphate. Furthermore, glyceraldehyde 3-phosphate is oxidized to 1, 3-bisphosphoglycerate. One phosphate group from the 1, 3-bisphosphoglycerate is transferred to ADP to produce an ATP. This produces a 3-phosphoglycerate molecule. The phosphate group of the 3-phosphoglycerate is transferred into the second carbon position of the same molecule to form a 2-phosphoglycerate molecule.  The removal of a water molecule from the 2-phosphoglycerate produces phosphoenolpyruvate (PEP). The transfer of the phosphate group of PEP to an ADP molecule produces pyruvate. The overall reactions of the glycolysis produce two pyruvate molecules, two NADH molecules, two ATP molecules, and two water molecules.

What is Chloroplastic Glycolysis

Chloroplastic glycolysis is the type of glycolysis that occurs in the chloroplasts. The glycolysis process of chloroplastic glycolysis is similar to the normal glycolysis process of the cell. But in plant cells, chloroplast also undergo glycolysis in the presence of higher glucose concentrations. It occurs in the cytosol. The Krebs cycle occurs inside the chloroplast. The Krebs cycle of cytosolic glycolysis occurs inside the mitochondria.

Figure 2: Chloroplast

Moreover, the breakdown of glucose molecules in chloroplastic glycolysis results in the production of two pyruvate molecules along with two NADH molecules and two ATP molecules, similar to cytosolic glycolysis.  

Similarities Between Cytosolic and Chloroplastic Glycolysis

• Cytosolic and chloroplastic glycolysis are two processes that involve the breakdown of glucose molecules into two pyruvate molecules.
• It produces ATP.
• Several enzymes are involved in both processes.
• Both undergo Krebs Cycle.
• They occur in the cytosol.

Difference Between Cytosolic and Chloroplastic Glycolysis

Definition

Cytosolic glycolysis refers to a metabolic pathway that creates ATP without the use of oxygen but can occur in the presence of oxygen, while chloroplastic glycolysis refers to the process of oxidizing hexoses to provide ATP, reducing power and pyruvate, and producing precursors for anabolism.

Occurrence

Cytosolic glycolysis occurs in the cytosol, while the Krebs cycle of chloroplastic glycolysis occurs inside the chloroplast.

Importance

Moreover, cytosolic glycolysis occurs continuously, while chloroplastic glycolysis occurs in the presence of glucose in higher concentrations.

Conclusion

In brief, cytosolic and chloroplastic glycolysis are two processes that occur in the cytosol. Their function is to break down glucose molecules into two pyruvate molecules to use in the Krebs cycle. Cytosolic glycolysis is a linear process that occurs continuously in the cytosol in the presence of glucose. The Calvin cycle of cytosolic glycolysis occurs inside the mitochondria. On the other hand, chloroplastic glycolysis is the energy production process of chloroplast; the Krebs cycle of the process occurs inside the chloroplast. Moreover, this occurs in the presence of higher concentrations of glucose in the chloroplast. Therefore, this is the main difference between cytosolic and chloroplastic glycolysis.

References:

1. “Glycolysis.” Wikipedia. Wikimedia Foundation. 
2. Anoman AD, Flores-Tornero M, Rosa-Telléz S, Muñoz-Bertomeu J, Segura J, Ros R. The specific role of plastidial glycolysis in photosynthetic and heterotrophic cells under scrutiny through the study of glyceraldehyde-3-phosphate dehydrogenase. Plant Signal Behav. 2016;11(3):e1128614. doi: 10.1080/15592324.2015.1128614. Erratum in: doi: 10.1104/pp.15.00696. PMID: 26953506; PMCID: PMC4883961.

Image Courtesy:

1. “Glycolysis metabolic pathway 3 annotated” By Thomas Shafee – Own work (CC-BY 4.0) via Commons Wikimedia
2. “Scheme Chloroplast-en.” By User:Miguelsierra, adapted by User:Vossman – Own Work (CC-BY SA 4.0) via Commons Wikimedia