HMP shunt and its significance

• The HMP shunt (Hexose Monophosphate), also known as the Pentose Phosphate Pathway (PPP), is a crucial cytoplasmic pathway that supports cellular functions such as NADPH production and ribose-5-phosphate synthesis.
• It is essential for biosynthetic processes and protection against oxidative stress.

HMP Shunt Pathway / Phases of the HMP Shunt

• The pathway is bifurcated into two main phases: the oxidative phase, which generates NADPH, and the non-oxidative phase, which produces ribose-5-phosphate and allows for the interconversion of sugar phosphates.

1. Oxidative Phase:

   • Glucose-6-phosphate Dehydrogenation: Converts glucose-6-phosphate to 6-phosphoglucono-δ-lactone, producing NADPH.
   • Lactonase Action: Converts 6-phosphoglucono-δ-lactone to 6-phosphogluconate.
   • Decarboxylation: 6-phosphogluconate is decarboxylated to ribulose-5-phosphate, generating more NADPH.

2. Non-Oxidative Phase:

   • Interconversions: Converts ribose-5-phosphate, ribulose-5-phosphate, and xylulose-5-phosphate.
   • Formation of Glycolytic Intermediates: Transketolase and other enzymes convert sugar phosphates into glycolytic intermediates like fructose-6-phosphate and glyceraldehyde-3-phosphate.

Significance of the HMP Shunt

1. NADPH Production:

   • Supports anabolic processes like fatty acid and cholesterol synthesis.
   • Maintains reduced glutathione, protecting cells from oxidative stress.

2. Ribose-5-phosphate Production:

   • Essential for nucleotide and nucleic acid synthesis, critical for rapidly dividing cells (e.g., immune and bone marrow cells).

3. Metabolic Flexibility:

   • Allows cells to balance between energy production (via glycolysis) and the need for biosynthetic precursors, providing adaptability in response to metabolic demands.

• This streamlined overview highlights the importance of the HMP shunt in cellular metabolism and defense against oxidative damage.

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