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?

Verified step by step guidance

1. Step 1: Understand the metabolic pathway structure. You have five substrates (1-5) and five enzymes (A-E). Each enzyme catalyzes a reaction between two substrates, leading to the next substrate in the sequence.
2. Step 2: Visualize the pathway: Substrate 1 is converted to Substrate 2 by Enzyme A, Substrate 2 to Substrate 3 by Enzyme B, Substrate 3 to Substrate 4 by Enzyme C, Substrate 4 to Substrate 5 by Enzyme D, and finally, Substrate 5 to the product nirvana by Enzyme E.
3. Step 3: Identify the role of Enzyme C. Enzyme C is responsible for converting Substrate 3 to Substrate 4.
4. Step 4: Consider the effect of a nonfunctional Enzyme C. If Enzyme C is nonfunctional, it cannot catalyze the conversion of Substrate 3 to Substrate 4.
5. Step 5: Determine which molecule accumulates. Since Substrate 3 cannot be converted to Substrate 4, Substrate 3 will accumulate in the 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 this scenario, if enzyme C is nonfunctional, the substrate immediately before it in the pathway will accumulate, as it cannot be converted into the next product.

Substrate Accumulation

Substrate accumulation occurs when a specific substrate cannot be converted into its product due to a malfunctioning enzyme. This buildup can have various physiological effects on the organism, potentially leading to toxicity or altered metabolic states. Identifying which substrate accumulates helps in understanding the impact of the mutation on the overall metabolic pathway and the organism's health.