Pentose Phosphate Pathway
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– This is also called the Phosphogluconate pathway or Hexose monophosphate shunt
– Ribose 5-Phosphate – Precursor in Nucleotide Biosynthesis of RNA and DNA, NAD(P)+ and CoASH
-NOT REQUIRED FOR ENERGY PRODUCTION
• Net consumer of ATP
• 2 moles NADPH
• Ribose-5-phosphate (5-C sugar)- Recycling
• Dispersal of excess C-5 carbon units
• Glycolytic intermediates eventually produced
NADP+ is the electron acceptor
Although ring opening occurs in the absence of a catalyst, the lactonase speeds up the reaction
The OH at C3 (C2 of product) is oxidized to a ketone. This promotes loss of the carboxyl at C1 as CO2.NADP+ behaves as an oxidant, accepting H from the oxidised components
Pathway, it is the first step of the first phase. This enzyme is regulated by availability of the substrate NADP+.As NADPH is utilised in reducing synthetic pathways, the increasing concentration of
NADP+ stimulates the Pentose Phosphate Pathway, to replenish NADPH.
ribulose-5-P and xylulose-5-P.
Isomerase converts the ketose ribulose-5-P to the aldose ribose-5-P.
Both reactions involve deportation to an endiolate intermediate followed by specific re-protonation to yield the product.
Both reactions are reversible.
(GAP) and sedoheptulose 7- phosphate from two pentoses. It does this by transfering 2-C fragment from xylulose-5-P to ribose-5-P.Transketolase uses prosthetic group thiamine pyrophosphate (TPP), a derivative of vitamin B12
This produces Fructose-6- phosphate for glycolysis.
Glycolysis converts all g-6-p to GAP and f-6-p. Then phase 2 of pentose phosphate pathway can use these to make ribose-5 phosphate.MODE 2: needs of ribose 5-phosphate and NADPH balanced. Pentose Phosphate pathway mainly uses its oxidaWve part (phase 1) only.
MODE 3: more NADPH needed than ribose 5-phosphate (e.g. synthesis of faVy acids). All of pentose phosphate pathway used and the resultant GAP and f-6-p molecules synthesized back to g-6-p by gluconeogenesis.
MODE 4: both NADPH and ATP required. Same as Mode 3 except GAP and f-6-p go into glycolysis.
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