Examine the biosynthetic pathway for the production of the amino acids tryptophan, tyrosine, and phenylalanine in the figure. Where do the initial reactants (erythrose 4-phosphate and PEP) originate?

Verified step by step guidance

1. Identify the metabolic pathways that produce erythrose 4-phosphate and phosphoenolpyruvate (PEP) as intermediates. These compounds are key intermediates in central metabolism.
2. Recall that erythrose 4-phosphate is an intermediate in the pentose phosphate pathway, which is a branch of carbohydrate metabolism responsible for generating NADPH and sugar phosphates.
3. Recognize that phosphoenolpyruvate (PEP) is an intermediate in glycolysis, the pathway that breaks down glucose to pyruvate while generating ATP and NADH.
4. Understand that both erythrose 4-phosphate and PEP are derived from glucose metabolism: erythrose 4-phosphate from the pentose phosphate pathway and PEP from glycolysis.
5. Conclude that the initial reactants for the biosynthesis of tryptophan, tyrosine, and phenylalanine originate from glucose catabolism through the pentose phosphate pathway (erythrose 4-phosphate) and glycolysis (PEP).

Key Concepts

Shikimate Pathway

The shikimate pathway is a metabolic route in bacteria, fungi, and plants that synthesizes aromatic amino acids like tryptophan, tyrosine, and phenylalanine. It begins with the condensation of erythrose 4-phosphate and phosphoenolpyruvate (PEP) to form chorismate, the precursor for these amino acids.

Erythrose 4-Phosphate Origin

Erythrose 4-phosphate is an intermediate of the pentose phosphate pathway, which operates parallel to glycolysis. It is derived from the rearrangement of sugar phosphates and provides the carbon skeleton necessary for aromatic amino acid biosynthesis.

Phosphoenolpyruvate (PEP) Origin

Phosphoenolpyruvate (PEP) is a high-energy intermediate produced during glycolysis. It serves as a key reactant in the shikimate pathway, contributing to the formation of aromatic amino acids by combining with erythrose 4-phosphate.