Which event contradicts the central dogma of molecular biology? a. Poly-A polymerase enzymes process mRNA in the nucleus. b. Endonuclease enzymes splice out and repair damaged DNA. c. Scientists use reverse transcriptase enzymes to make DNA from RNA. d. Codons specifying amino acids are degenerate and universal.
The correct answer and explanation is:
Correct Answer: c. Scientists use reverse transcriptase enzymes to make DNA from RNA.
The central dogma of molecular biology describes the flow of genetic information in cells as a one-way process: DNA → RNA → Protein. This framework, first proposed by Francis Crick in 1958, suggests that DNA is transcribed into RNA, which is then translated into proteins. Proteins are the functional products that perform various roles within the cell. According to the central dogma, information cannot flow backward from RNA to DNA.
However, the process of reverse transcription contradicts this model. Reverse transcription involves the synthesis of DNA from an RNA template using an enzyme called reverse transcriptase. This enzyme was first discovered in retroviruses such as HIV (Human Immunodeficiency Virus). These viruses carry their genetic material in the form of RNA. When they infect a host cell, reverse transcriptase converts their RNA into DNA, which then integrates into the host genome and directs the production of viral components.
This backward flow of information from RNA to DNA is not accounted for in the original central dogma. Therefore, the use of reverse transcriptase by scientists and viruses is a direct contradiction to the classic one-directional model.
The other options are consistent with the central dogma. For instance, Poly-A polymerase processing mRNA (option a) is a post-transcriptional modification, endonucleases repairing DNA (option b) maintain the integrity of the DNA molecule, and the universality and degeneracy of codons (option d) support the translation phase of the central dogma. Thus, none of these events challenge the direction of information flow.
In summary, reverse transcription is the event that contradicts the central dogma, showing that genetic information can, under certain conditions, flow from RNA back to DNA.