Pentose Phosphate Pathway Overview
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Questions and Answers

Which enzyme catalyzes the first reaction in the oxidative phase of the Pentose Phosphate Pathway?

  • Transketolase
  • Lactonase
  • 6-Phosphogluconate dehydrogenase
  • Glucose-6-phosphate dehydrogenase (correct)

What is produced during the oxidative phase of the Pentose Phosphate Pathway?

  • Glucose
  • ATP
  • Ribulose 5-phosphate
  • NADPH (correct)

Which of the following pathways is parallel to glycolysis?

  • Pentose Phosphate Pathway (correct)
  • Citrate cycle
  • Gluconeogenesis
  • Beta-oxidation

What is the primary function of ribose 5-phosphate in the Pentose Phosphate Pathway?

<p>Synthesis of nucleotides and nucleic acids (D)</p> Signup and view all the answers

What type of reactions primarily utilize NADPH generated in the Pentose Phosphate Pathway?

<p>Anabolic reactions (A)</p> Signup and view all the answers

What is the role of transketolase and transaldolase in the non-oxidative phase of the Pentose Phosphate Pathway?

<p>Non-oxidative synthesis of pentoses (B)</p> Signup and view all the answers

Which molecule is formed by the decarboxylation of 6-phosphogluconate in the Pentose Phosphate Pathway?

<p>D-ribulose 5-phosphate (C)</p> Signup and view all the answers

Where in the cell does the Pentose Phosphate Pathway predominantly occur?

<p>Cytosol (C)</p> Signup and view all the answers

Flashcards

Pentose Phosphate Pathway (PPP)

An alternative metabolic pathway to glycolysis, producing NADPH, ribose 5-phosphate, and erythrose 4-phosphate.

Oxidative phase

The first, non-reversible phase of PPP, creating NADPH.

Glucose 6-phosphate dehydrogenase

Enzyme initiating the oxidative phase of PPP, converting glucose 6-phosphate.

NADPH

Reducing agent crucial for reductive biosynthetic reactions.

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Ribose 5-phosphate

5-carbon sugar crucial for nucleotide synthesis.

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Transketolase and Transaldolase

Enzymes involved in the non-oxidative phase of PPP, converting sugars.

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Non-oxidative phase

The second, reversible phase of PPP, converting sugars.

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6-Phosphogluconate dehydrogenase

Enzyme in the oxidative phase of PPP which oxidizes and decarboxylates 6-phosphogluconate, forming ribulose.

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Study Notes

Pentose Phosphate Pathway (PPP)

  • Glucose is broken down via glycolysis into pyruvate, and then further oxidized in the citric acid cycle to produce ATP in animal tissues.
  • The PPP is an alternative metabolic pathway.
  • Also known as the Hexose Monophosphate Pathway (HMP shunt) or Phosphogluconate pathway.
  • This pathway produces ribose sugar, ATP, and two NADPH.
  • The PPP is a parallel metabolic pathway to glycolysis.
  • It does not directly produce ATP.
  • Occurs in the cytosol of cells.
  • Key locations in the body include liver, adipose tissue, lactating mammary gland, and the cortex of the adrenal gland.

PPP Function

  • Generates reducing equivalents (NADPH) for reductive biosynthesis reactions (e.g., fatty acid synthesis).
  • Produces ribose 5-phosphate (R5P) for nucleotide and nucleic acid synthesis.
  • Produces erythrose 4-phosphate (E4P) for aromatic amino acid synthesis.

PPP Phases

  • Oxidative Phase (non-reversible):
    • Glucose 6-phosphate undergoes dehydrogenation and decarboxylation, producing ribulose 5-phosphate.
    • This phase generates NADPH.
  • Non-oxidative Phase (reversible):
    • Ribulose 5-phosphate is converted back to glucose 6-phosphate through a series of reactions involving transketolase and transaldolase.
    • This phase is important for shuffling carbon atoms.

Key Enzymes in the Oxidative Phase

  • Glucose-6-phosphate dehydrogenase (G6PD): Oxidizes glucose 6-phosphate to form 6-phosphoglucono-lactone and NADPH.
  • Lactonase: Hydrolyzes 6-phosphoglucono-lactone to 6-phosphogluconate.
  • 6-Phosphogluconate dehydrogenase: Oxidizes and decarboxylates 6-phosphogluconate to form ribulose 5-phosphate and CO2, while producing NADPH.

Key Enzymes in the Non-Oxidative Phase

  • Phosphopentose isomerase: Converts ribulose 5-phosphate to ribose 5-phosphate.
  • Phosphopentose epimerase: Converts ribulose 5-phosphate to xylulose 5-phosphate.
  • Transketolase: Transfers a two-carbon unit from a ketose to an aldose.
  • Transaldolase: Transfers a three-carbon unit from a ketose to an aldose.

Regulation of the PPP

  • Glucose-6-phosphate dehydrogenase is the rate-limiting enzyme.
  • The pathway is regulated allosterically by NADPH.
  • It is induced by high glucose/insulin to glucagon ratios after carbohydrate meals.

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Description

This quiz explores the Pentose Phosphate Pathway (PPP), an alternative metabolic pathway that plays a crucial role in producing ribose sugar and NADPH. Understand its function, phases, and importance in various tissues like liver and adipose. Test your knowledge on how the PPP operates alongside glycolysis.

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