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.) (b) Suppose a mutant strain can survive if substrate 5 is added to the growth medium, but it cannot grow if substrates 1, 2, 3, or 4 are added. Which enzyme in the pathway is affected in this mutant?

Verified step by step guidance

1. Step 1: Draw the metabolic pathway starting with substrate 1. Label this substrate as S1. Enzyme A catalyzes the reaction between S1 and the next substrate, S2, forming S2.
2. Step 2: Continue the pathway by having enzyme B catalyze the reaction between S2 and the next substrate, S3, forming S3. Repeat this process with enzyme C and substrate S4, and enzyme D with substrate S5.
3. Step 3: Conclude the pathway with enzyme E catalyzing the final reaction between S5 and the product nirvana.
4. Step 4: Analyze the mutant strain's growth conditions. Since the mutant can survive with the addition of S5 but not with S1, S2, S3, or S4, it indicates that the enzyme catalyzing the reaction just before S5 is likely defective.
5. Step 5: Identify the defective enzyme. Since S5 can be converted to the product nirvana in the presence of enzyme E, and the mutant strain can grow when S5 is added, enzyme D, which catalyzes the reaction forming S5, is likely affected in this mutant.