Questions and Answers
What is the main function of NADPH in cellular processes?
Which enzyme acts as the rate-limiting step in the oxidative phase of the Pentose Phosphate Pathway?
Which of the following products is NOT formed in the oxidative phase of the Pentose Phosphate Pathway?
What metabolic pathway does the Pentose Phosphate Pathway run parallel to?
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What is the main reason the TCA cycle is referred to as an amphibolic pathway?
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Which compound is generated by the action of 6-phosphogluconate dehydrogenase?
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Which of the following intermediates is linked to fatty acids and sterols?
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Which amino acids are linked to a-ketoglutarate and participate in various biosynthetic pathways?
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Which enzyme converts Pyruvate into Oxaloacetate?
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What type of reactions are depicted in red within the TCA cycle diagram?
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Which compound is produced from the conversion of Oxaloacetate by PEP carboxykinase?
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Which of the following is linked to Oxaloacetate?
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Which molecules are associated with Succinyl-CoA based on their metabolic links?
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Study Notes
Pentose Phosphate Pathway (PPP)
- Also known as Phosphogluconate or Hexose Mono Phosphate (HMP) Shunt.
- Functions parallel to glycolysis, providing alternative metabolic routes.
Oxidative Phase (Irreversible)
- Starts with Glucose-6-Phosphate and involves:
- Conversion by Glucose-6-Phosphate dehydrogenase, the rate-limiting enzyme.
- Production of NADPH and 6-phosphoglucono-d-lactone.
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6-Phosphogluconate is formed through further hydrolysis:
- Acts as a substrate for 6-phosphogluconate dehydrogenase, generating more NADPH and leading to the formation of Ribulose-5-phosphate.
Functions of NADPH
- Essential for:
- Cholesterol synthesis
- Fatty acid synthesis
- Reduction of Glutathione, which protects cells from reactive oxygen species (ROS).
Nonoxidative Phase (Reversible)
- Involves interconversion of sugars:
- Ribulose-5-phosphate
- Ribose-5-phosphate
- Fructose-6-phosphate
- Links to the glycolytic pathway, facilitating the biosynthesis of nucleotides and other important molecules.
Key Enzymes in Oxidative Phase
- Glucose-6-Phosphate dehydrogenase: Initial enzyme, crucial for NADPH production.
- 6-Phosphogluconate dehydrogenase: Converts 6-phosphogluconate to Ribulose-5-phosphate, also produces NADPH.
Nucleotide Synthesis
- PPP contributes significantly to the biosynthesis of nucleotides, which are vital for DNA and RNA synthesis.
Amphibolic Nature of TCA Cycle
- TCA cycle is both catabolic and anabolic, termed as an amphibolic pathway.
- Intermediates from the TCA cycle are essential precursors for various biosynthetic pathways.
Diagram of the TCA Cycle
- The TCA cycle includes key molecules: Citrate, Isocitrate, a-ketoglutarate, Succinyl-CoA, Oxaloacetate, and Malate.
- Pyruvate is connected to Acetyl-CoA, Oxaloacetate, and Malate, indicating its central role in metabolism.
- Significant connections with other biomolecules include:
- Glucose linked to Phosphoenolpyruvate (PEP).
- Citrate associated with fatty acids and sterols.
- a-ketoglutarate & Glutamate linked to Glutamine, Proline, and Arginine.
- Purines connected to Glutamate.
- Succinyl-CoA linked to porphyrines and heme.
Enzymatic Conversions
- Pyruvate carboxylase: Catalyzes conversion of Pyruvate to Oxaloacetate.
- PEP carboxykinase: Converts Oxaloacetate to Phosphoenolpyruvate (PEP).
- Malate enzyme: Facilitates conversion of Pyruvate to Malate.
Additional Molecule Linkages
- Amino acids Serine, Glycine, Cysteine, Phenylalanine, Tyrosine, and Tryptophan are linked to Phosphoenolpyruvate (PEP).
- Aspartate and Asparagine are associated with Oxaloacetate.
- Pyrimidines are linked to Asparagine.
Anaplerotic Reactions
- Key reactions replenish depleted intermediates in the citric acid cycle.
- Intermediates are utilized as precursors in various biosynthetic pathways.
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Description
This quiz explores the Pentose Phosphate Pathway (PPP), including its oxidative and nonoxidative phases. You'll learn about the key enzymes, metabolic processes involved, and the significance of NADPH in various biosynthetic pathways. Test your knowledge on this essential metabolic route in biochemistry!
