Which mode of information transfer usually does not occur?

RUHS, Jaipur, M.Sc Nursing Entrance Exam-2016

Pathology & Genetics

Easy

Appeared in: RUHS, Jaipur, M.Sc Nursing Entrance Exam-2016

Explanation

The Central Dogma of Molecular Biology states that genetic information flows from DNA to RNA to protein.
Direct synthesis of protein from a DNA template is not a known biological process.
The process requires an intermediate step called transcription (DNA to RNA) followed by translation (RNA to protein).
Messenger RNA (mRNA) acts as the carrier of the genetic code from the DNA in the nucleus to the protein-synthesis machinery (ribosomes) in the cytoplasm.

Option A: The transfer of information from DNA to DNA is a fundamental process known as replication. It occurs every time a cell divides to ensure that each new daughter cell receives a complete set of genetic instructions.
Option B: The transfer of information from DNA to RNA is a core process called transcription. It is the first step in gene expression, where a gene's DNA sequence is copied (transcribed) into an RNA molecule.
Option D: This option is incorrect because one of the listed processes, DNA to protein, does not occur directly. Therefore, not all listed transfers happen in a working cell.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Central Dogma of Molecular Biology as background academic context rather than a clinical decision trigger.
Understanding the central dogma is fundamental to modern medicine, as many diseases are caused by errors in this pathway (genetic mutations).
Many antibiotics work by targeting these processes. For example, Rifampicin inhibits bacterial transcription (DNA to RNA), while tetracyclines and macrolides inhibit bacterial translation (RNA to protein).
Antiviral drugs for retroviruses like HIV, such as reverse transcriptase inhibitors, work by blocking the reverse flow of information from RNA back to DNA, a notable exception to the central dogma.

How to Approach the Question

First, identify the core concept being tested, which is the flow of genetic information, also known as the Central Dogma of Molecular Biology.
The question asks which process does not occur. This requires you to evaluate each option against the known biological pathway.
Recall the steps of the central dogma: DNA can be replicated to make more DNA (Replication). DNA's code is copied into RNA (Transcription). RNA's code is used to build a protein (Translation).
Evaluate Option A (DNA to DNA): This is replication. It occurs.
Evaluate Option B (DNA to RNA): This is transcription. It occurs.
Evaluate Option C (DNA to protein): Think about the pathway. Is there a direct mechanism for a ribosome to read DNA and make a protein? No, it reads mRNA. Therefore, this direct transfer does not occur.

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