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Pentose Phosphate Pathway

The pentose phosphate pathway, also known as the hexose monophosphate shunt, is an alternative pathway to glycolysis that occurs in the cytosol. It has two phases: the oxidative phase produces NADPH and the non-oxidative phase produces pentoses like ribulose 5-phosphate. The pathway generates reducing power in the form of NADPH and produces pentoses that are important for nucleotide and nucleic acid synthesis.

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Sania Saeed
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180 views10 pages

Pentose Phosphate Pathway

The pentose phosphate pathway, also known as the hexose monophosphate shunt, is an alternative pathway to glycolysis that occurs in the cytosol. It has two phases: the oxidative phase produces NADPH and the non-oxidative phase produces pentoses like ribulose 5-phosphate. The pathway generates reducing power in the form of NADPH and produces pentoses that are important for nucleotide and nucleic acid synthesis.

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Sania Saeed
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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HEXOSE

MONOPHOSPHATE
PATHWAY
(PENTOSE PHOSPHATE PATHWAY)
This is an alternate pathway to glycolysis and TCA cycle
for the oxidation of glucose.
SITE : It is located in a cytosol . The tissues such as liver,
adipose tissue , adrenal gland ,erythrocytes , testes and
lactating mammary gland are highly active in HMP Shunt.
REACTIONS OF THE PATHWAY
1)OXIDATIVE PHASE: G6PD Is an NADP dependent enzyme
that converts glucose 6 phosphate to 6 phosphogluconolactone. The
latter is then hydrolysed by the gluconolactone hydrolase to 6
phosphogluconate. Next reaction involving the synthesis of NADPH is
catalysed by 6 phosphogluconate dehydrogenase to produce 3 keto 6
phosphogluconate which undergoes decarboxylation to give ribulose 5
phosphate.
Overview
Function
◦ NADPH production
◦ Reducing power carrier
◦ Synthetic pathways
◦ Role as cellular antioxidants
◦ Ribose synthesis
◦ Nucleic acids and nucleotides
NADPH producing reactions
Glucose-6-P dehydrogenase
6-P-gluconate dehydrogenase
Characteristics:
Oxidative and Non-oxidative Phases
Oxidative phases
◦ Reactions producing NADPH
◦ Irreversible

Non-oxidative phases
◦ Produces ribose-5-P
◦ Reversible reactions feed to glycolysis
2) NON OXIDATIVE PHASE: It is concerned with
interconversion of three,four ,five and seven carbon monosacchrides.
Ribulose 5 phosphate is acted upon by epimerase to produce Xylulose 5
phosphate while ribose 5 phosphate ketoisomerase converts ribulose 5
phosphate to ribose 5 phosphate. The enzyme transketolase catalyse
the transfer of two carbon moiety from xylulose 5 phosphate to ribose 5
phosphate to form GA3P and sedoheptulose 7 phosphate.Transketolase
is dependent on TPP and Mg ions. Transaldolase brings about transfer of
3 carbon from S7P to GA3P to form fructose 6 phosphate and erythrose
4 phosphate.
The Pentose Phosphate Pathway:
Non-oxidative phases
REGULATION OF HMP SHUNT
# The entry of G6P into HMP pathway is controlled by
concentration of NADPH.
#NADPH is inhibitor of G6P DH.
# The Synthesis of G6P DH is induced by increased
insulin/glucagon after a meal.
SIGNIFICANCE: HMP Pathway generates two important
products
1. Pentose
2. NADPH
IMPORTANCE OF NADPH
#It is required for reductive biosynthesis of fatty acids and steroids.
#It is used in synthesis of certain amino acids involving the enzyme
Glutamate dehydrogenase.
#Microsomal cytochrome P 450 brings about detoxification of drugs
involving NADPH.
#Phagocytosis by WBC requires supply of NADPH.
#NADPH produce in RBC preserve the integrity of RBC membrane.

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