Question

The discovery of which of the following enzymes challenged the central dogma of molecular biology and why? A. Reverse transcriptase, because transcription was thought to be unidirectional only from DNA to RNA B. Reverse transcriptase, because transcription was thought to be unidirectional only from 5? to 3? and never 3? to 5? C. Integrase, because the central dogma did not account for movement of DNA within the chromosome D. Integrase, because the central dogma did not account for the existence of DNA outside of the nucleus

Short answer

A. Reverse transcriptase, because transcription was thought to be unidirectional only from DNA to RNA

Step-by-step solution

Understanding the Central Dogma

The central dogma of molecular biology states that genetic information flows from DNA to RNA to protein. This means that DNA is transcribed into RNA, which is then translated into proteins.

Analyzing the Candidate Enzymes

Identify the enzymes given in the options and understand their functions. Reverse transcriptase synthesizes DNA from an RNA template. Integrase integrates viral DNA into a host genome.

Evaluation of Reverse Transcriptase

Consider the role of reverse transcriptase. This enzyme contradicted the central dogma by showing that RNA could be reverse transcribed into DNA, thus making the information flow bidirectional (RNA to DNA).

Evaluation of Integrase

Consider the role of integrase. Integrase mediates the insertion of viral DNA into a host cell's genome, which does not necessarily challenge the overall directionality of genetic information flow described by the central dogma.

Selecting the Correct Enzyme

Based on the above evaluations, reverse transcriptase is the enzyme that challenged the central dogma. The central dogma initially assumed that transcription (DNA to RNA) was the only process, and reverse transcription (RNA to DNA) was not known.

Choosing the Correct Explanation

Given that reverse transcriptase was thought to challenge the unidirectional flow of transcription from DNA to RNA, option A is correct.

Key concepts

Reverse Transcriptase

Reverse transcriptase is a remarkable enzyme. It violates the traditional flow of genetic information as described by the central dogma of molecular biology. This enzyme catalyzes the synthesis of DNA from an RNA template. Before its discovery, scientists believed that genetic information flowed only in one direction: from DNA to RNA to protein.

Reverse transcriptase was first discovered in retroviruses. These viruses use RNA as their genetic material, and when they infect a host cell, they utilize reverse transcriptase to convert their RNA into DNA. This newly synthesized DNA can then integrate into the host's genome, allowing the virus to hijack the host's cellular machinery for replication.

This discovery was groundbreaking because it demonstrated a previously unknown genetic pathway: RNA to DNA. It showed that genetic information could be transferred from RNA molecules back to DNA, challenging the unidirectional view of genetic flow. Reverse transcriptase is now a crucial tool in molecular biology, particularly in techniques such as reverse transcription-polymerase chain reaction (RT-PCR), which is used to measure gene expression.

Unidirectional Transcription

Unidirectional transcription refers to the process by which genetic information is copied from DNA to RNA in a single direction. This concept was a cornerstone of the central dogma of molecular biology, which posited that genetic information flowed in a one-way path: DNA ➡️ RNA ➡️ Protein.

In classic transcription, an enzyme called RNA polymerase binds to specific regions of the DNA, known as promoters, and synthesizes a complementary RNA strand. This RNA strand then undergoes processing to become messenger RNA (mRNA), which serves as a template for protein synthesis during translation.

The discovery of reverse transcriptase shattered the assumption of unidirectional transcription. It became clear that the flow of genetic information was not as rigid as previously thought. While traditional transcription moves information from DNA to RNA, reverse transcription allows the information to move in the opposite direction, from RNA back to DNA.

This flexibility in genetic information transfer provided deeper insights into genetic regulation and the complexity of life’s molecular machinery.

RNA to DNA Transcription

RNA to DNA transcription is a process that became widely known through the discovery of reverse transcriptase. Unlike the typical transcription process, where DNA is used to create RNA, this involves the synthesis of DNA from an RNA template.

This process is particularly significant in the context of retroviruses. When a retrovirus infects a cell, it uses reverse transcriptase to convert its RNA genome into DNA. This viral DNA then integrates into the host cell's DNA, enabling the virus to replicate and produce new virus particles using the host's cellular machinery.

The ability of certain organisms to reverse transcribe RNA into DNA has immensely impacted genetic research and biotechnology. For example, in the laboratory, scientists use reverse transcriptase to create complementary DNA (cDNA) from RNA. This cDNA is often used in cloning and gene expression studies.

Thus, RNA to DNA transcription is not merely a biological curiosity; it’s a fundamental aspect of modern molecular biology and biotechnology, demonstrating the dynamic nature of genetic information transfer.