Glucose Degradation via the Hexose Monophosphate Pathway (Pentose Phosphate Pathway)

Glucose Degradation via the Hexose Monophosphate Pathway (Pentose Phosphate Pathway)

The Hexose Monophosphate Pathway (HMP), also known as the Pentose Phosphate Pathway, is a metabolic pathway for glucose that occurs alongside glycolysis. This pathway does not directly produce ATP energy but focuses on producing NADPH and Ribose-5-phosphate.

# Main Reactions:

Step 1:

• 3 molecules of Glucose-6-phosphate (G-6-P) react with 6 molecules of NADP+ and 3 molecules of water to produce 2 molecules of G-6-P, 1 molecule of Glyceraldehyde-3-phosphate (P-glyceraldehyde), 6 molecules of NADPH+H+, and 3 molecules of CO2.

• This reaction is catalyzed by the enzyme Glucose-6-phosphate dehydrogenase.

Step 2:

• P-glyceraldehyde can be converted to G-6-P (equivalent to 1/2 G-6-P) to continue the cycle.

# Why is it called the Pentose Pathway?

The Pentose Phosphate Pathway is named as such because it is a closed loop where the final products are used as raw materials for subsequent reactions. It is called the Pentose pathway because it generates 5-carbon sugars (pentoses) like Ribose-5-phosphate.

# Pentose Pathway and the Hexose Diphosphate Pathway:

The Pentose Phosphate Pathway runs parallel to the Hexose Diphosphate Pathway (glycolysis). These two pathways can exchange intermediate products with each other.

# Percentage of the Pentose Pathway:

The Pentose Phosphate Pathway accounts for approximately 7-10% of the glucose degraded in the body.

# The Most Important Significance of the Pentose Phosphate Pathway:

• Production of NADPH+H+: NADPH+H+ is a specific coenzyme that acts as a hydrogen donor in the synthesis of fatty acids, cholesterol, and steroid hormones.

• Protecting cells from oxidative stress: NADPH+H+ helps convert oxidized Glutathione to its reduced form, facilitating the breakdown of H2O2 (Hydrogen Peroxide) into H2O. This reaction is crucial in red blood cells to protect the cell membrane from oxidation and destruction, preventing hemolysis.

# Where does the Pentose Pathway take place?

The Pentose Phosphate Pathway occurs in the cytoplasm of cells because the enzymes catalyzing the pathway are located in the cytoplasm.

# Where is the Pentose Pathway predominant?

The Pentose Phosphate Pathway is predominant in liver cells, red blood cells, and mammary glands.

# Significance of the Pentose Phosphate Pathway:

In addition to producing NADPH+H+ and protecting cells from oxidative stress, the Pentose Phosphate Pathway plays a vital role in:

• Nucleic acid synthesis (DNA and RNA): Ribose-5-phosphate is a key raw material for DNA and RNA synthesis.

# Conclusion:

The Pentose Phosphate Pathway is a crucial metabolic pathway that plays an essential role in producing NADPH+H+, protecting cells from oxidative stress, and synthesizing nucleic acids.