5. Pentose phosphate
pathway
The pentose phosphate pathway is a metabolic pathway that plays a crucial
role in the production of biochemical molecules in the cell.
6. The Two Phases of the Pathway
1 Oxidative Phase
This phase generates NADPH and
ribose 5-phosphate, which are
required for nucleotide metabolism
and biosynthesis.
2
Non-Oxidative Phase
This phase involves the formation
and interconversion of 5 and 6
carbon sugars.
7. The Oxidative Phase: Enzymes and
Reactions
Glucose-6-
Phosphate
Dehydrogenase
The enzyme that catalyses
the oxidative decarboxylation
of glucose-6-phosphate to 6-
phosphogluconolactone.
6-
Phosphogluconat
e Dehydrogenase
The enzyme that catalyses
the oxidative decarboxylation
of 6-phosphogluconate to
ribulose-5-phosphate.
NADP+
The electron acceptor that is
reduced to NADPH during
the oxidative phase.
8. The Non-Oxidative Phase: Reactions
and Products
Transketolase
The enzyme that transfers
two-carbon units from a
ketose sugar to an aldose
sugar, leading to the
formation of ribose-5-
phosphate and
glyceraldehyde-3-
phosphate.
Transaldolase
The enzyme that transfers
three-carbon units
between ketose and
aldose sugars.
Products
The non-oxidative phase
generates a pool of
intermediates that can be
used for nucleotide and
amino acid biosynthesis.
9.
10. The Role of the Pathway in Nucleotide
Synthesis
DNA
The building block of DNA is
nucleotides, which are
synthesized from
intermediates of the pentose
phosphate pathway.
ATP
The pentose phosphate
pathway produces NADPH,
which is required for the
reduction of glutathione and
synthesis of ATP.
RNA
Ribose-5-phosphate, a
product of the non-oxidative
phase, is an important
precursor for RNA synthesis.
11. Regulation of the Pathway
The pentose phosphate pathway is regulated by the cellular demand for NADPH and ribose-5-
phosphate. It is also regulated by the activity of the enzymes glucose-6-phosphate dehydrogenase and
6-phosphogluconate dehydrogenase.
12. Conclusion and
Significance of the Pathway
in Metabolism
1 Metabolic Pathway
The pentose phosphate
pathway is an important
metabolic pathway that
connects glucose
metabolism to nucleotide
and amino acid
biosynthesis.
2 Redox Balance
The pathway plays a crucial
role in maintaining redox
balance in the cell by
producing NADPH, which
acts as an electron donor in
many metabolic reactions.
3 Disease States
Deficiencies in the enzymes of the pentose phosphate pathway can
lead to various diseases and disorders such as haemolytic anaemia
and glucose-6-phosphate dehydrogenase deficiency.
