Even though most know that DNA serves as the genetic blueprint for all life, most do not understand how this blueprint is read. In 1958, scientist Francis Crick proposed the theory that the transfer of genetic material flows in one direction: DNA → RNA → Protein [1, 2]. His idea was eventually coined “The Central Dogma of Molecular Biology, and it is the basis of how biological systems operate.
Deoxyrubonucleic acid (DNA)
DNA houses the genes of an organism in the nucleus. It consists of a double helix structure (two strands), primarily composed by the nucleotide bases adenine (A), thymine (T), cytosine (C) and guanine (G). The sequence of these bases determine the genetic code and different orders of these bases can create different genes.
Figure 1. DNA molecule [3].
The initial step of the central dogma is DNA replication, wherein the DNA molecule is unwound and each strand of the molecule is used as a template for the synthesis of a new complementary strand. This ensures that the genetic information of the new copy is essentially identical to the original.
Ribonucleic acid (RNA)
RNA is produced using DNA as a template. Therefore, even though RNA is structurally similar to DNA, it is instead mostly single-stranded, less stable, more versatile, and consists of the bases A, C, G, and uracil (U).
Figure 2. RNA molecule [4].
The process to create an RNA molecule is known as transcription. This process relies on the use of an enzyme known as RNA polymerase, which binds to a specific region of DNA and synthesizes a single-stranded complementary RNA strand, which ends up in the cytoplasm. There are multiple types of RNA depending on their role, most commonly: messenger (mRNA), transfer (tRNA), and ribosomal RNA (rRNA).
mRNA tells the cell which proteins need to be made.
tRNA serves as a link between mRNA and specific amino acids during protein synthesis.
rRNA creates proteins for ribosomes.
Protein
The final step in the dogma is the transition from RNA to protein, by a process known as translation. Once the mRNA is in the cytoplasm, ribosomes scan its sequence in search of the AUG start sequence (called codon) to begin translation. For each nucleotide base read, the tRNA adds a specific amino acid into the protein chain. This ends once the ribosome encounters the stop codon (UAA, UAG, or UGA).
After translation, the protein chain will undergo a process called folding. The chemical properties of the amino acids fold the protein chain carefully, and different folds lead to different proteins produced. This folding is crucial to perform its specific function in the cell. If something goes in disarray, it can lead to malfunctions.
Figure 3. Translation process [5].
Is the Central Dogma really natural law?
It was once believed that the central dogma was only unidirectional, meaning DNA → RNA → Protein. However, like most things in biology, there are instances where this is not the case. Retroviruses like HIV actually challenge the dogma, as their genetic information flows from RNA → DNA. Another example are infectious proteins known as prions, which can replicate themselves independently of DNA and RNA. Prions cause rare, progressive, and fatal neurological diseases such as Mad Cow or Creutzfeldt-Jakob disease. Although the central dogma is not completely accurate, it serves as a useful tool to understand how most genetic information is utilized and has played a crucial role in understanding many phenomena in medicine, biotechnology, and genetic engineering.
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Written by: Renard
Edited by: Natasha and Maria
BioDecoded is a volunteer group committed to sharing accurate scientific information. We cannot offer any specific health advice. If you have any questions about this topic or would like to learn more, please comment below, or send us your questions.
References:
Central Dogma (2023). National Human Genome Research Institute. Available at: https://www.genome.gov/genetics-glossary/Central-Dogma# (Accessed: 6 July 2023).
Cobb, M. (2017) "60 years ago, Francis Crick changed the logic of biology", PLOS Biology, 15(9). Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5602739/#:~:text=These%20were%20protein%20%E2%86%92%20protein,This%20is%20the%20central%20dogma
Deoxyribonucleic Acid (DNA) (2023). National Human Genome Research Institute. Available at: https://www.genome.gov/genetics-glossary/Deoxyribonucleic-Acid (Accessed: 6 July 2023).
What is RNA? (2023). Your Genome. Available at: https://www.yourgenome.org/facts/what-is-rna/ (Accessed: 6 July 2023).
Peptide (2023). National Human Genome Research Institute. Available at: https://www.genome.gov/genetics-glossary/Peptide (Accessed: 6 July 2023).
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