Question

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

Short answer

The molecule that would accumulate in the affected cells due to the nonfunctional enzyme C is substrate 3. The enzyme affected in the mutant strain that can survive with substrate 5 but not with substrates 1, 2, 3, or 4 is enzyme E.

Step-by-step solution

Draw and label the metabolic pathway

Consider the following 5 enzymes \(A, B, C, D, E\), and 5 substrates numbered as \(1, 2, 3, 4, 5\). We can create a metabolic pathway connecting these substrates using the enzymes as follows: \(1 \xrightarrow{A} 2 \xrightarrow{B} 3 \xrightarrow{C} 4 \xrightarrow{D} 5 \xrightarrow{E} \text{Biological Sciazine} \) Here, substrate 1 reacts with enzyme A to generate substrate 2, and so on, and the final product formed is Biological Sciazine.

Determine the molecule that accumulates with enzyme C mutation

If enzyme C is nonfunctional due to a mutation, the reaction that converts substrate 3 to substrate 4 won't occur. As a result, substrate 3 will accumulate in the affected cells.

Determine the affected enzyme for the mutant strain that can survive with substrate 5

The mutant strain can't grow if substrates 1, 2, 3, or 4 are added, but it can survive with substrate 5. This suggests that the problem is in the pathway occurring after, and including, substrate 5 conversion. Since enzyme E catalyzes the reaction involving substrate 5, enzyme E must be affected in this mutant strain.

Key concepts

Neurospora crassa

Neurospora crassa is a species of red bread mold that has long been a model organism in genetics and molecular biology. It is used in scientific experiments due to its simplicity and rapid life cycle. Scientists can easily induce mutations in its genes to study various biological processes. The organism’s DNA is relatively simple and can be modified to help understand genetic functions. Researchers often use Neurospora crassa to examine metabolic pathways because it helps clarify the role of enzymes in these pathways.
Through Neurospora crassa, scientists can observe how genetic changes affect cell processes and study enzyme activities in detail. The organism's relevance is significant for understanding metabolic pathways and gene-enzyme relationships.

Enzyme Mutation

An enzyme mutation is a change in the DNA sequence of the gene that encodes for an enzyme. This mutation can alter the enzyme's structure, affecting its ability to catalyze reactions. In metabolic pathways, each enzyme has a specific task, and any alteration can disrupt the entire pathway.
For instance, in our hypothetical pathway, a mutation making enzyme C nonfunctional prevents substrate 3 from being converted to substrate 4, halting the production of the final product, Biological Sciazine. - Enzyme mutations can lead to accumulation of substrates at the point of failure. - It can also lead to downstream effects, altering other metabolic processes.
Understanding the impact of enzyme mutations is crucial for genetic research and biotechnology applications.

Substrate Accumulation

Substrate accumulation occurs when a metabolic pathway is interrupted, often by an enzyme malfunction, resulting in an excess of a substrate. In the absence of a functioning enzyme, the specific substrate cannot be converted into the subsequent substrate in the pathway.
In the case of enzyme C being nonfunctional in Neurospora crassa, substrate 3 accumulates because it cannot be converted into substrate 4. This is a common diagnostic characteristic of enzyme deficiencies in metabolic pathways. - Accumulation of a substrate can be harmful and cause cellular stress or damage. - Recognizing accumulated substrates helps identify the point of failure within the pathway.
Addressing substrate accumulation can involve supplementing pathways with missing components or compensating for failed enzymatic reactions.

Enzyme Function

Enzyme function is crucial in metabolic pathways, acting as biological catalysts that speed up reactions between substrates. Each enzyme is specific to a particular reaction, ensuring that pathways proceed efficiently and effectively. Enzymes lower the activation energy of reactions, allowing processes to occur at rates that support life.
For example, in the hypothetical pathway of Neurospora crassa discussed, each enzyme (A through E) catalyzes a specific reaction, ensuring a smooth progression from substrate 1 to the creation of Biological Sciazine. - Enzyme specificity is critical for pathway integrity. - If any enzyme in the sequence is nonfunctional due to mutation, it disrupts the overall pathway flow.
Understanding the function of each enzyme within a pathway enables researchers to predict effects of mutations and devise interventions to restore functionality.