Pentose Phosphate Pathway

Pentose Phosphate Pathway - o Adjustments according to cell...

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Pentose Phosphate Pathway (aka hexose monoP shunt or Pgluconate pathway) o cells require NADPH for reductive biosynthetic rxns o this pathway allows glu to provide reducing power (e- in form of NADPH) and carbon compounds for biosynthetic rxns o liver is major site o provides NADPH required for fatty acid synthesis in cells o steps (first steps are oxidative) 2 oxidative rxns provide NADPH for biosynthesis non-oxidative rxns provide ribose-5-P for biosynthesis of nucleotides The products of the non-oxidative branch (fructose-6- phosphate and glyceraldehyde-3-phosphate) can be returned to glycolysis or gluconeogenesis 1: NADP + reduced to NADPH 3: generates NADPH 4+: series of molecular rxns that generate fruct-6-P and glyceraldehydes-3-P o NADPH (and intermediates of fatty acid biosynthesis) allosterically inhibits glu-6-P dehydrogenase [this and other mechanisms help partition glu btwn glycolysis and pentose P pathway according to cell’s requirements]
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Unformatted text preview: o Adjustments according to cell requirements: • when both ribose-5-P and NADPH are required • oxidative part of pentose pathway dominates & ribose-5-P and NADPH are used for biosynthesis (no C to glycolysis) • when more ribose-5-P than NADPH is required • fruct-6-P and glycrealdehyde-3-P from glycolysis are fed into non-oxidative part of pentose P pathway (runs in reverse to make ribose-5-P w/ no generation of NADPH; no C to glycolysis) • when more NADPH than ribose-5-P is required • rxns o 6 glu-6-P + 12 NADP + 6 ribose-5-P + 12 NADPH + 6 CO 2 (pentose pathway) o 6 ribose-5-P 4 fruct-6-P + 2 glyceraldehyde-3-P o 4 fruct-6-P + 2 glyceraldehyde-3-P 5 glu-6-P (gluconeogensis) • net rxn: glu-6-P + 12 NADP + 6 CO 2 + 12 NADPH • when both NADPH and ATP are needed, but ribose-5-P isn’t • like above, except fruct-6-P & glyceraldehyde-3-P are fed into glycolysis to make ATP...
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This note was uploaded on 02/09/2010 for the course BIOL 3361 taught by Professor Zhang/spiro during the Fall '08 term at Dallas.

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Pentose Phosphate Pathway - o Adjustments according to cell...

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