Introduces the pentose phosphate pathway as a cytoplasmic alternative to glycolysis, then goes through its key enzymes in order, from glucose-6-phosphate dehydrogenase through to transketolase and transaldolase. It covers the pathway's roles in NADPH generation and ribose-5-phosphate supply, its regulation, and its links to disease, with a section on G6PD deficiency covering clinical features, mechanism, management and prevention. It ends with four multiple-choice questions, though their answers are left blank.
Topic 21 of 70 in the MU Sofia syllabus for Biochemistry (Medicine, Year 2). The free AceMed note covers it in 12 sections, about 951 words (7 min of reading), with 10 flashcards.
In this note
Introduction
Introduction to the Pentose Phosphate Pathway (PPP):
Key Enzymes and Reactions:
Functions of the Pentose Phosphate Pathway:
Regulation of the Pentose Phosphate Pathway:
Physiological and Pathological Implications:
Importance of the Pentose Phosphate Pathway (PPP):
Oxidative, Isomerase, and Transferase Reactions:
Glucose-6-Phosphate Dehydrogenase Deficiency:
Conclusion:
MCQs
Answers
Introduction to the Pentose Phosphate Pathway (PPP):
The PPP is a metabolic pathway occurring in the cytoplasm of cells.
It serves as an alternative route for glucose metabolism alongside glycolysis.
The pathway plays crucial roles in generating NADPH and providing ribose-5-phosphate for nucleotide synthesis.
Key Enzymes and Reactions:
Glucose-6-Phosphate Dehydrogenase (G6PD):
Catalyzes the first and rate-limiting step of the PPP.
Converts glucose-6-phosphate (G6P) to 6-phosphogluconolactone.
NADP+ is reduced to NADPH during this step.
6-Phosphogluconolactonase:
Hydrolyzes 6-phosphogluconolactone to 6-phosphogluconate.
6-Phosphogluconate Dehydrogenase:
Catalyzes the oxidative decarboxylation of 6-phosphogluconate.
Yields ribulose-5-phosphate and another molecule of NADPH.
Ribulose-5-Phosphate Isomerase:
Converts ribulose-5-phosphate to ribose-5-phosphate, an essential precursor for nucleotide synthesis.
Transketolase and Transaldolase:
Enzymes involved in interconversions between pentose phosphates and glycolytic intermediates.
Facilitate the production of various sugar phosphates used in biosynthetic pathways.
Functions of the Pentose Phosphate Pathway:
NADPH Generation:
NADPH serves as a reducing equivalent in biosynthetic reactions, particularly lipid synthesis and the detoxification of reactive oxygen species (ROS).
Critical for maintaining cellular redox balance and protecting against oxidative stress.
Ribose-5-Phosphate Production:
Ribose-5-phosphate is a precursor for the synthesis of nucleotides (purines and pyrimidines), which are essential for DNA and RNA synthesis.
Supports cell proliferation and growth by providing necessary building blocks for nucleic acid synthesis.
Reductive Biosynthesis:
The PPP generates reducing power in the form of NADPH required for the synthesis of fatty acids, cholesterol, and steroids.
Facilitates the regeneration of reduced glutathione (GSH), an important antioxidant molecule.
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