Pentose Phosphate Pathway Flashcards
A 13-year-old boy is diagnosed with glucose-6-phosphate dehydrogenase (G6PD) deficiency after developing back pain following the consumption of a dish made with fava beans. G6PD is the rate determining enzyme in which of the following metabolic processes?
Pentose Phosphate Pathway
Main explanation
Glucose-6-phosphate dehydrogenase catalyzes the dehydrogenation of glucose-6-phosphate to yield 6-phosphogluconate in the pentose phosphate pathway (PPP). G6PD is the rate-determining enzyme of PPP. The key regulators of this enzyme include:
- Activator: NADP+
- Inhibitor: NADPH
Major takeaway
Glucose-6-phosphate dehydrogenase is the rate-determining enzyme of the pentose phosphate pathway. It is regulated by NADP+ (activator) and NADPH (inhibitor).
products of PPP: 2 NADPH & Ribose-5-phosphate (5 carbon sugar)
Biochemistry researchers are studying the pentose phosphate pathway (PPP) as an alternative route for the metabolism of glucose. Which of the following is a major function of PPP?
Main explanation
The pentose phosphate pathway is an alternative route for the metabolism of glucose. It does not lead to formation of ATP but has two major functions: (1) the formation of NADPH for synthesis of fatty acids and steroids and maintaining reduced glutathione for antioxidant activity and (2) the synthesis of ribose for nucleotide and nucleic acid formation.
Major takeaway
Pentose phosphate pathway is the source of NADPH and yields ribose for nucleotide synthesis.
Ribose is used to make nucleotides which are the building blocks of DNA & RNA
What are hte 2 phases of the Pentose Phosphate Pathway?
The sequence of reactions of the pentose phosphate pathway may be divided into two phases:
- An irreversible oxidative phase: Glucose-6-phosphate undergoes dehydrogenation and decarboxylation to yield ribulose-5-phosphate and NADPH.
- Reversible non-oxidative phase: Ribulose-5-phosphate is converted back to glucose-6-phosphate by a series of reactions involving mainly two enzymes: transketolase and transaldolase.
Both phases function independently depending on the cellular requirements.
transketolase = 2 carbon transfer
transaldolase = 3 carbon transfer
The pentose phosphate pathway takes place in the (location) ____________ of the cell.
cytoplasm
The final step in the oxidative phase of the pentose phosphate pathway is the oxidative decarboxylation of 6-phosphogluconate into …
ribulose-5-phosphate
The products of the ____________ in the cytosol of the cell are two NADPH, one carbon dioxide molecule, and ribose-5-phosphate to be used for the building of DNA and RNA.
pentose phosphate pathway
The first step in the oxidative phase of the pentose phosphate pathway is the oxidation of ____________ to 6-phosphogluconolactone.
glucose-6-phosphate
The product of the oxidative phase and first molecule of the non-oxidative phase of the pentose phosphate pathway, ________________ , is the precursor to the sugar that makes up DNA and RNA.
ribulose-5-phosphate
