Principles of Molecular Biology
Principles
The central principle or the Central Dogma of molecular biology proposes that genetic information is transferred from DNA to RNA, and from RNA to protein, which is comprised of the following three phenomena:
- Replication: DNA replicates itself.
- Transcription: RNA, which contains the same information as DNA, is synthesized.
- Translation: Proteins are synthesized according to the information in RNA.
Explanation
The Central Dogma was an hypothesis proposed by Francis Crick in 1958, who is also famous for discovering the double helix structure of DNA. As the name implies, it is incredibly important in molecular biology. It succinctly and accurately explains the process by which genes are expressed and proteins are produced. Initially, it was argued that the process occurred strictly in the sequence of replication→transcription→translation, without any reverse course.
Replication
Replication is, as the term implies, the phenomenon where DNA makes an exact copy of itself. When the double helix of DNA splits into two strands, DNA polymerase moves along each strand, creating the opposite strand. Base pairs match up in a complementary manner as $A-T$, $G-C$, so the exact opposite sequence of bases can be reproduced on one strand from the other.
Transcription
The term transcription is not commonly used in everyday life, but it can be simplified to something like copying down. RNA is a copy of DNA that is not exactly the same but sufficient for reading genetic information. RNA polymerase divides the two strands of DNA and creates RNA by matching complementary base pairs.
Translation
RNA exits the nucleus, and within a ribosome, amino acids bond together to form proteins.
If we use computer science as an analogy, in object-oriented programming, DNA corresponds to an object (Object), and mRNA corresponds to an instance (Instance). The reason why it is not directly going from DNA to protein but instead making it complicated is explained by the fact that treating DNA as read-only and working with its copy, mRNA, is more stable in terms of genetic data management.
Why mRNA?
On the other hand, the reason why we specifically use the term mRNA instead of just RNA is because in eukaryotic cells, mRNA transcribed in the cell nucleus ’transmits’ genetic information outside the nuclear membrane, and the term RNA itself is not exclusive to the RNA mentioned in the Central Dogma. Originally, by definition, RNA was sufficient to be a polymer in the form of a nucleotide chain, and there are some bacteria that store genetic information with only RNA. In short, not all RNA is transcribed from DNA.