Role of the Pentose phosphate pathway
- produce NADPH
- generate ribose-5-phosphate (a five carbon sugar, name of the pathway) - sugar component for nucleotides (DNA and RNA)
Currency of reducing power for most reductive biosynthetic reactions
NADPH
Starting point of the pathway
Glucose 6 P
(Interconnects PPP w glycolysis)
PPP carried out in the ____
Cytosol
Equivalent of PPP in plants (to make NADPH)
Photosynthesis
(In animals, PPP active in tissues where the synthesis of biomolecules occurs at high rates)
Oxidative phase
G6P gets oxidized and NADPH is produced (NADP+ reduced)
- G6P —> 6-Phosphogluconolactone —> 6-Phosphogluconate —> Ribulose-5-Phosphate + CO2
- Enzymes:
(1) G6P Dehydrogenase: oxidized G6P, NADP+ reduced to NADPH
(2) Lactonase
(3) 6-phosphogluconate dehydrogenase: another NADPH produced
Non oxidative phase
- Ribulose-5-P converted to Ribose-5-P
- interconversion of 3-, 4-, 5-, 6-, and 7-carbon sugars (a way for the excess 5 carbon sugars to be converted to glycolysis intermediates)
- no NADPH formed
Second major product of the pathway
Ribose-5-P
Number of NADPH produced for every G6P entering the ppp pathway
2
Ribulose-5-P
5 carbon sugar, end product of the oxidative phase
What enzyme converts ribulose5P to Ribose5P
Phosphopentose isomerase
