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 substrates and enzymes in the metabolic pathway. Since the pathway consists of five substrates (1-5) and five enzymes (A-E), arrange them in a sequential order where each enzyme catalyzes the reaction between consecutive substrates.
2. Visualize the pathway: Substrate 1 is converted by enzyme A to Substrate 2, Substrate 2 is converted by enzyme B to Substrate 3, Substrate 3 is converted by enzyme C to Substrate 4, Substrate 4 is converted by enzyme D to Substrate 5, and finally, Substrate 5 is converted by enzyme E to the product nirvana.
3. Understand the effect of the mutation on enzyme C: If enzyme C is nonfunctional due to a mutation, it cannot catalyze the conversion of Substrate 3 to Substrate 4.
4. Determine the accumulation: Since enzyme C is nonfunctional, Substrate 3 cannot be converted to Substrate 4 and will accumulate in the cells.
5. Consider the downstream effects: The accumulation of Substrate 3 might also affect the levels of Substrates 4 and 5, and the final product nirvana, as these subsequent reactions depend on the product of the reaction catalyzed by enzyme C.

Key Concepts

Metabolic Pathways

Metabolic pathways are 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 products. Understanding these pathways is crucial for analyzing how mutations can affect metabolic processes and lead to the accumulation of specific molecules.

Enzymes and Their Function

Enzymes are biological catalysts that speed up chemical reactions in metabolic pathways by lowering the activation energy required for the reaction to occur. Each enzyme is specific to its substrate and plays a critical role in determining the flow of metabolites through the pathway. A mutation that renders an enzyme nonfunctional can halt the pathway at that point, leading to the accumulation of substrates preceding the affected enzyme.

Effects of Mutations on Metabolism

Mutations in genes encoding enzymes can disrupt normal metabolic functions, leading to the accumulation of specific substrates. In the context of Neurospora crassa, if enzyme C is nonfunctional due to a mutation, the substrates that precede enzyme C in the pathway will not be converted into the next product. This results in the buildup of the substrate immediately before enzyme C, which is essential for predicting the metabolic consequences of such mutations.