Draw a hypothetical metabolic pathway in Neurospora crassa composed of five substrates, five enzymes, and a product called nirvana. Number the substrates 1–5, and label the enzymes A–E, in order. (For instance, enzyme A catalyzes the reaction between substrates 1 and 2.) (a) Suppose a mutation made the gene for enzyme C nonfunctional. What molecule would accumulate in the affected cells?

Key Concepts

Metabolic Pathway

A metabolic pathway is a series of chemical reactions occurring within a cell, where substrates are converted into products through the action of enzymes. Each step in the pathway is catalyzed by a specific enzyme, which facilitates the transformation of substrates into intermediate compounds and ultimately into the final product. Understanding the sequence and function of these reactions is crucial for analyzing the effects of mutations on metabolic processes.

Enzyme Function and Mutations

Enzymes are biological catalysts that speed up chemical reactions by lowering the activation energy required. A mutation that renders an enzyme nonfunctional can disrupt the entire metabolic pathway, leading to the accumulation of substrates that precede the blocked reaction. In the context of Neurospora crassa, if enzyme C is nonfunctional, the substrate immediately before enzyme C in the pathway will accumulate, as it cannot be converted into the next substrate.

Substrate Accumulation

Substrate accumulation occurs when a specific substrate cannot be converted into its product due to a malfunctioning enzyme. This buildup can indicate where in the metabolic pathway the disruption has occurred. In the case of the hypothetical pathway in Neurospora crassa, identifying which substrate accumulates when enzyme C is nonfunctional helps to pinpoint the metabolic block and understand the pathway's dynamics.