biochem mini lecture Pentose Phosphate Pathway (PPP)

Overview of the Pentose Phosphate Pathway (PPP)

  • Commonly referred to as BPP or Triple P.

Key Concepts

  • Understanding NADPH:
    • NADPH (Nicotinamide adenine dinucleotide phosphate): A crucial molecule for biosynthesis, particularly in fatty acid and cholesterol synthesis.
    • Structure comparison with NADH:
      • NADPH has a hydroxyl group at the first nucleotide, while NADH contains a hydrogen atom.

Function of Pentose Phosphate Pathway

  • Produces NADPH and ribose-5-phosphate.
  • Ribose-5-phosphate is essential for nucleic acid synthesis and can contribute to the synthesis of fatty acids.

Phases of the Pentose Phosphate Pathway

  • Occurs in the cytosol of liver and adipose tissues.
  • Two main phases of the pathway:
    1. Oxidative Phase (first two steps, irreversible):
    • Key processes involve oxidation reactions of metabolites.
    1. Non-oxidative Phase (reversible processes):
    • Utilizes sugars to produce intermediates for glycolysis.

Details of the Oxidative Phase

  1. Convert glucose-6-phosphate (G6P) into 6-phosphogluconate.
  2. Convert 6-phosphogluconate to ribulose-5-phosphate via oxidative decarboxylation using 6-phosphogluconate dehydrogenase.

Non-Oxidative Phase Steps

  1. Isomerization of ribulose-5-phosphate to xylulose-5-phosphate.
    • Conversion of ketone to aldehyde without enzyme negativity; a necessary reaction.
  2. Combination of xylulose-5-phosphate and ribose-5-phosphate to produce intermediates necessary for glycolysis, including G3P (glyceraldehyde-3-phosphate) and fructose-6-phosphate.
    • Critical for cellular energy needs and entering the TCA cycle.

Importance of Intermediates and Regulation

  • NADPH production is critical; regulated primarily by the first step of the oxidative phase.
  • Enzyme: Glucose-6-phosphate dehydrogenase (G6PD) is activated by NADP+ and inhibited by NADPH.

Xylulose-5-Phosphate

  • Major byproduct of non-oxidative steps, can influence metabolic pathways depending on its presence or absence:
    • High levels can stimulate glycolysis and fatty acid synthesis while regulating glycogen production in the liver.
    • Plays a key regulatory role in the flow of metabolites based on cellular sugar levels.