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. Identify the sequence of the metabolic 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.
2. Understand that a nonfunctional Enzyme C means it cannot catalyze the conversion of Substrate 3 to Substrate 4.
3. Recognize that if Enzyme C is nonfunctional, Substrate 3 will not be converted to Substrate 4 and will accumulate in the cells.
4. Consider the implications of this accumulation: Substrate 3 will build up because it cannot be processed further down the pathway.
5. Conclude that the accumulation of Substrate 3 is due to the blockage in the pathway caused by the nonfunctional Enzyme C.

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 case, 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 in the metabolic pathway. 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 and the role of each enzyme in the pathway.