Question

Which one of the following is NOT a path of genetic information flow as per the modern Central Dogma of Biology ?

• A. DNA ----$>$ RNA ----$>$ Protein
• B. RNA ----$>$ RNA
• C. RNA ----$>$ DNA
• D. Protein ----$>$ DNA

Hint:

Prions are infectious proteins that can alter the folding conformation of other normal proteins, but even they do not transfer sequence information back to DNA or RNA.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
The Central Dogma of Molecular Biology, formulated by Francis Crick in 1958 and updated in 1970, describes the flow of sequential genetic information within a biological system.

Step 2: Detailed Explanation:
The modern Central Dogma describes three distinct classes of genetic information transfer:
1. General Transfers: These occur in almost all living cells.
- DNA replication (DNA $\rightarrow$ DNA)
- Transcription (DNA $\rightarrow$ RNA)
- Translation (RNA $\rightarrow$ Protein)
Thus, the pathway DNA $\rightarrow$ RNA $\rightarrow$ Protein (A) is a standard general transfer pathway.
2. Special Transfers: These occur only under specific conditions, such as in certain viral infections.
- Reverse Transcription (RNA $\rightarrow$ DNA), catalyzed by the enzyme reverse transcriptase in retroviruses (C).
- RNA Replication (RNA $\rightarrow$ RNA), catalyzed by RNA-dependent RNA polymerases in RNA viruses (B).
3. Unknown/Impossible Transfers: Transfer of genetic information from protein back to nucleic acids (Protein $\rightarrow$ DNA or Protein $\rightarrow$ RNA) does not occur.
There is no molecular machinery or biochemical mechanism capable of translating the primary structure of a protein back into a specific nucleic acid sequence.
Therefore, Protein $\rightarrow$ DNA is not a valid path of genetic information flow.

Step 3: Final Answer:
The pathway that is not a valid flow of genetic information is Protein ----$>$ DNA, corresponding to option (D).