16 - Pentose Phosphate Pathway

PENTOSE PHOSPHATE PATHWAY

also called the hexose monophosphate shunt or the phosphogluconate pathway

1. NADPH

2. pentoses; ribose-5-P

3. pentoses; oxidation; glycolysis

PENTOSE PHOSPHATE PATHWAY

• Functions:

  1. To generate reducing power in the form of ________

  2. To generate __________ from hexoses (______________)

  3. To convert excess ___________ back to hexoses for ____________ via __________

1. NADPH

   • reductive biosynthesis; detoxification processes

2. Ribose-5-phosphate

   • nucleic acids

PRODUCTS OF PENTOSE PHOSPHATE PATHWAY

1. ________

   • phosphorylated NADH but the two are not interconvertible

   • used in ___________________ (eg. synthesis of lipids and nucleotides) and in __________________

2. ______________

   • required in the synthesis of ____________ especially in actively dividing cells

1. Oxidative

   • NADPH

   • irreversible

2. Non-oxidative

   • 5-C

   • glycolysis

STAGES OF PENTOSE PHOSPHATE PATHWAY

1. __________ Stage

   • oxidative generation of _________

   • _____________ steps

2. _________________ Stage

   • interconversion of 3, 4, 5, 6 and 7-carbon sugars that results in the synthesis of ___ sugars

   • serves as the link of PPP to __________

STAGES OF PENTOSE PHOSPHATE PATHWAY -

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• cyclic este

STAGES OF PENTOSE PHOSPHATE PATHWAY - ___________________

• main regulatory step in PPP

• lactone is a ____________

STAGES OF PENTOSE PHOSPHATE PATHWAY -

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STAGES OF PENTOSE PHOSPHATE PATHWAY - ___________________

• hydrolysis of the lactone to yield a carboxylate

STAGES OF PENTOSE PHOSPHATE PATHWAY -

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STAGES OF PENTOSE PHOSPHATE PATHWAY - ___________________

• oxidative decarboxylation to yield ribulose-5-P and CO2

STAGES OF PENTOSE PHOSPHATE PATHWAY -

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• glucose-6-phosphate dehydrogenase

• glucose 6-phosphate

REGULATION OF OXIDATIVE STAGE

• When NADPH is formed faster than it is used, the [NADPH] increases and inhibits ____________________________

• more _____________________ is available for glycolysis

• ribose-5-P

  • nucleotide biosynthesis

• xylulose-5- phosphate

STAGES OF PENTOSE PHOSPHATE PATHWAY -

• ribulose-5-P is converted to its aldose isomer _____________

  • The isomer is a precursor for __________________

• ribulose-5-P is epimerized to _______________

STAGES OF PENTOSE PHOSPHATE PATHWAY - NON-OXIDATIVE STAGE (Rearrangements)

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STAGES OF PENTOSE PHOSPHATE PATHWAY - NON-OXIDATIVE STAGE (Rearrangements)

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Vitamin B1 (as its active coenzyme form, thiamine pyrophosphate or TPP) acts as an essential cofactor for the enzyme transketolase

STAGES OF PENTOSE PHOSPHATE PATHWAY - NON-OXIDATIVE STAGE (Rearrangements)

• What is the importance of vitamin B1 on the non-oxidative stage of the PPP?

STAGES OF PENTOSE PHOSPHATE PATHWAY -

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STAGES OF PENTOSE PHOSPHATE PATHWAY -

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MODES OF THE PENTOSE PHOSPHATE PATHWAY -

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MODES OF THE PENTOSE PHOSPHATE PATHWAY -

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Mode 3: Only NADPH is needed

MODES OF THE PENTOSE PHOSPHATE PATHWAY - _______________

• in adipose tissues for synthesis of fatty acids

Mode 3: Only NADPH is needed

MODES OF THE PENTOSE PHOSPHATE PATHWAY - _______________

• both oxidative and non-oxidative phases are active

Mode 3: Only NADPH is needed

MODES OF THE PENTOSE PHOSPHATE PATHWAY - _______________

• while NADPH is generated in the oxidative phase, ribose-5-P enters the non-oxidative phase for regeneration of Glc-6-P

Mode 3: Only NADPH is needed

MODES OF THE PENTOSE PHOSPHATE PATHWAY - _______________

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• ɣ-glutamylcysteylglycine

GLUTATHIONE

• __________________ (reduced form)

essential for maintaining the normal structure of red blood cells (iron is maintained in the ferrous state)

_______________

• detoxifies reactive oxygen species (peroxides) with ________________ enzyme

• GSH or glutathione (reduced form)

Glucose 6-Phosphate dH Deficiency

• insufficient production of NADPH which results eventually into insufficient _____________________

Glucose 6-Phosphate dH Deficiency - due to lack of GSH or glutathione (reduced form)

• cells cannot fight oxidative stress

• cells are susceptible to hemolysis (hemolytic anemia)