What is the reverse transcription exception to the central dogma?

• A. RNA is reverse transcribed into DNA by reverse transcriptase, which can then be integrated into the host genome.
• B. DNA is reverse transcribed into RNA.
• C. Protein is reverse transcribed into DNA.
• D. RNA is not used in transcription.

Answer: (A)

The main idea is that information can flow from RNA back to DNA in a specific biological context. Some viruses, called retroviruses, carry an enzyme called reverse transcriptase that uses viral RNA as a template to synthesize complementary DNA. That DNA can then integrate into the host genome and become part of the cell’s genetic material. Once integrated, the host’s machinery can transcribe that DNA to produce viral RNAs and proteins. This RNA-to-DNA step is the reverse transcription exception to the usual DNA→RNA→protein flow described by the central dogma. The other options describe directions or processes that don’t occur in this context, so they don’t capture the true exception.