Glucose Degradation via the Hexosediphosphate Pathway

Glucose Degradation via the Hexosediphosphate Pathway

Glucose degradation is the process of breaking down glucose to release energy. There are two main pathways for glucose degradation: the hexosediphosphate pathway (also known as the pentose phosphate pathway) and the hexosemonophosphate pathway. This article will focus on the hexosediphosphate pathway.

The Hexosediphosphate Pathway:

• Where does it occur? Cytoplasm of the cell.

• Initial step: Glucose is converted to glucose 6-phosphate (G6P) by the enzyme glucokinase or hexokinase.

• Next step: G6P is converted to fructose 6-phosphate (F6P) by the enzyme phosphohexose isomerase.

• Continuing: F6P is converted to fructose 1,6-bisphosphate (F1,6BP) by the enzyme phosphofructokinase.

• Splitting: F1,6BP is split into dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (G3P) by the enzyme aldose.

• G3P metabolism:

• G3P is converted to 1,3-bisphosphoglycerate (1,3BPG) by the enzyme glyceraldehyde 3-phosphate dehydrogenase.

• 1,3BPG is converted to 3-phosphoglycerate (3PG) by the enzyme phosphoglycerate kinase.

• 3PG is converted to 2-phosphoglycerate (2PG) by the enzyme phosphoglycerate mutase.

• 2PG is converted to phosphoenolpyruvate (PEP) by the enzyme enolase.

• PEP is converted to pyruvate (enol) by the enzyme pyruvate kinase.

• Pyruvate (enol) spontaneously converts to pyruvate (ketone).

Further Degradation Pathway:

• Anaerobic: Oxygen-deficient environment, primarily occurring in muscle and bone tissue.

• Pyruvate is converted to L-lactate by the enzyme lactate dehydrogenase, NADH+ is oxidized to NAD+.

• Pyruvate can also be fermented to ethanol (alcohol) through acetaldehyde, a process that occurs in some yeasts.

• Aerobic: Oxygen-rich environment, occurring in mitochondria.

• Pyruvate is converted to acetyl coenzyme A (acetyl-CoA) by the pyruvate dehydrogenase enzyme complex.

• Acetyl-CoA participates in the Krebs cycle to produce ATP, CO2, and H2O. NADH and FADH2 generated in the Krebs cycle enter the electron transport chain.

Note:

• From F1,6BP, the hexosediphosphate pathway splits into two branches, and the subsequent metabolic steps are doubled.

• Energy obtained from glucose degradation:

• Anaerobic: 2 ATP (from glucose), 3 ATP (from glycogen)

• Aerobic: 38 ATP (from glucose), 39 ATP (from glycogen)

• Glycogen degradation is more efficient than glucose degradation because glycogen is directly broken down into G1P, which is then converted to G6P, saving 1 ATP.

• Muscle fatigue: Due to lack of oxygen, the body switches to anaerobic glucose degradation, producing lactic acid accumulation, which causes muscle fatigue.

• Coconut water contains lactic acid and can cause muscle fatigue.

• Blood lactate levels can be tested to assess tissue oxygen deficiency or infection.

Significance of Glucose Degradation via the Hexosediphosphate Pathway:

• Provides energy for the cell.

• Generates intermediates for various other metabolic processes.

• Lactate is recycled for glucose synthesis.

Conclusion

The hexosediphosphate pathway is a crucial pathway in glucose degradation, providing energy for cells and producing intermediates for numerous other metabolic processes. This pathway can occur in two ways: anaerobically and aerobically, each offering its own benefits and limitations. Understanding the mechanisms of the hexosediphosphate pathway will help us better comprehend energy metabolism in the body.