Here's why:

* RNA and DNA are different molecules: RNA (ribonucleic acid) and DNA (deoxyribonucleic acid) have distinct structures and functions.

* RNA can be removed during DNA isolation: Standard DNA isolation protocols include steps to remove RNA, often using enzymatic digestion with RNase (ribonuclease).

Key terms you may be thinking of:

* Carrier DNA: This term sometimes refers to a specific type of DNA that is added during the isolation process to help with the precipitation of the target DNA. This carrier DNA is typically a known and inert DNA sequence that doesn't interfere with the analysis.

* RNA isolation: There are separate protocols for isolating RNA, where RNase inhibitors are used to protect the RNA from degradation.

In summary: RNA and DNA isolation are distinct processes, and there is no specific role for "carrier RNA" in DNA isolation.