Final answer:
Retroviruses, like HIV, do not encode for enzymes related to the host's essential cellular processes outside viral replication, such as those in the Krebs cycle or lipid metabolism. They do encode for reverse transcriptase necessary for their RNA to DNA conversion process.
Step-by-step explanation:
The enzymatic activities that are not encoded by a typical retrovirus, such as HIV, include those enzymes responsible for the essential cellular processes unrelated to viral replication. Retroviruses typically encode for reverse transcriptase, which is not found inside uninfected host cells but is crucial for converting their RNA genome into DNA to be incorporated into the host genome. However, enzymes for other metabolic and biosynthetic pathways, such as isocitrate dehydrogenase involved in the Krebs cycle, or enzymes specific to lipid metabolism like lipases, are generally not provided by the retrovirus's genome and rely on the host cell's machinery.