The Central Dogma of Molecular Biology: Understanding Genetic Information Flow

The central dogma of molecular biology describes the one-way flow of genetic information from DNA to RNA to proteins. First proposed by Francis Crick in 1958, this concept remains fundamental to our understanding of genetics, despite later discoveries that introduced exceptions. This article explores the central dogma, its processes, and the scientific developments that challenged its original premise.

The Flow of Genetic Information

Crick’s central dogma outlines three main steps:

1. Transcription – A section of DNA is copied into messenger RNA (mRNA), which serves as a template.
2. Translation – mRNA travels to the cytoplasm and binds to ribosomes, where it is read as codons (three-nucleotide sequences) that determine the order of amino acids in a protein.
3. Replication – DNA is faithfully copied to daughter cells through mitosis, ensuring genetic continuity.

The Discovery of Reverse Transcriptase

Originally, the central dogma suggested that genetic information could not flow backward from RNA to DNA. However, in 1970, Howard Temin and David Baltimore independently discovered the enzyme reverse transcriptase, which allows RNA to convert into DNA. This discovery, for which they received the 1975 Nobel Prize, proved that retroviruses like HIV could reverse the flow of genetic information.

The Role of Noncoding DNA

Another exception to the central dogma is the presence of noncoding DNA, which does not directly code for proteins. Surprisingly, about 98% of human DNA falls into this category, often referred to as "junk DNA", though its exact function is still under research.

Crick’s Reflections on "Dogma"

In his 1988 autobiography, What Mad Pursuit, Crick admitted that his use of the word "dogma" was misleading. Unlike a religious dogma, which is an unquestionable belief, scientific principles evolve with new discoveries—just as the central dogma did.

This image depicts the flow of genetic instructions from DNA, to RNA, to the production of amino acids, which link together to form proteins.