Final answer:
Catabolic enzymes are encoded by inducible genes, which increase the production of enzymes in response to the presence of a specific substrate, such as a nutrient the cell can use for energy. Constitutive genes, on the other hand, are expressed at a consistent level and are not dependent on the presence of substrates.
Step-by-step explanation:
The enzymes involved in catabolic pathways are typically encoded by inducible genes (option A). These are genes whose expression is upregulated or induced in the presence of a specific substrate, such as when a particular nutrient becomes available. Inducible genes produce enzymes that break down the nutrient into simpler molecules that the cell can use for energy and building blocks. An inducible operon is a good example of this genetic regulation mechanism; it remains off until the substrate is present.
Conversely, constitutive genes (option C) are those that are constantly expressed at a steady level and are responsible for the maintenance of basic cellular functions. Examples of constitutive genes include those that encode enzymes for glycolysis. In addition, genes of enzymes for the degradation of an unusual substrate might be inducible because they need only to be expressed when that substrate is present.
Therefore, enzymes required for the breakdown of common metabolites like glucose are typically encoded by constitutive genes, whereas enzymes needed for the breakdown of less commonly encountered substrates are often encoded by inducible genes.