Carbohydrate metabolism 5 - Pentose phosphate pathway

Overview of the Pentose Phosphate Pathway

Introduction to the Pathway

• The pentose phosphate pathway (PPP) is introduced as a crucial metabolic route, depicted in a simplified master diagram.

• It consists of two major variations that play distinct roles in cellular metabolism.

Key Functions and Products

• A significant function of both variations is the transfer of electrons from carbon to NADP+, resulting in the production of NADPH, an essential electron carrier for biosynthetic pathways.

• The fate of unoxidized carbon atoms differs between the two variations: they either enter glycolysis or are converted into ribose 5-phosphate for nucleotide synthesis.

First Variation: ATP Production

• In conditions where cells require both NADPH and ATP, glucose 6-phosphate is diverted from glycolysis to oxidize carbon into CO2 while generating NADPH.

• For every three glucose 6-phosphate molecules processed, three carbons are oxidized to CO2, yielding six NADPH molecules. The remaining carbons become intermediates in glycolysis leading to pyruvate production.

Second Variation: Nucleotide Synthesis

• The second variation prioritizes nucleotide synthesis; some carbon is still oxidized to CO2 for NADPH production.

• Here, instead of re-entering glycolysis, remaining carbons are transformed into ribose 5-phosphate, which serves as a building block for nucleotides.

Summary of Net Reactions