High School Biology and Chemistry TSS

Scientists Extend the DNA Alphabet

For most of the 20th century, it was widely accepted that DNA’s four bases were the only chemicals that could transfer genetic information and allow for life on Earth. That is, until scientists recently found that DNA could hold eight bases.

Deoxyribonucleic Acid (DNA) is composed of four bases: Guanine (C5H5N5O), Cytosine (C4H5N3O), Adenine (C5H5N5), and Thymine (C5H6N2O2), or GCAT, in short.

These bases determine the information available to build and maintain an organism by bonding in specific orders: C bonds with G, and A bonds with T, forming base pairs. Each base form hydrogen bonds with the nitrogen and oxygen molecules from its respective pair.

Hydrogen Bonding
In hydrogen bonding, the unbonded valance electrons in nonmetals like oxygen and nitrogen form a negative dipole, which attracts the positive dipole of hydrogen atoms, according to the Van Der Walls forces. This attractions holds DNA base pairs together.

Each base pair is also attached to a sugar molecule (C12H22O11) and a phosphate molecule (PO43-), forming a nucleotide. Sugar and phosphate form a double helix that twists around the four bases, forming DNA.

DNA Structure
DNA base pairs are the color-coded lines inside the helix, and the nucleotide forms the blue, twisted strand (the helix) surrounding the bases.

For a long time, scientists had been trying to find other chemicals that could replace these base pairs, speculating that our chemistry is not the only one that can support life. By modifying the existing bases, scientists have found, as of now, eight life-supporting bases.

Two of these bases were discovered in 2014, when scientists engineered E. Coli cells that produced this new genetic code. However, on February 20, scientist Steven Benner and his research group from Florida’s Foundation for Applied Molecular Evolution published a study that demonstrated the 2014 bases and how two new ones bind and form a double helix just like their natural counterparts, and therefore, they can transmit genetic information and support life, at least under controlled conditions.

Therefore, scientists have expanded DNA’s bases from GCAT to GCATSBPZ, using a system called Hajimoji (Japanese for ‘’eight letter’’). Now, DNA base pairs are: C and G, A and T, S and B, and P and Z. SBPZ stands for: 2-Aminoimidazo[1,2a][1,3,5]triazin-4(1H)-one (C5H5N5O), 6-Amino-5-nitropyridin-2-one (C5H5N3O3), Isoguanine (C5H5N5O), and Isocytosine (C4H5N3O)/1-Methylcytosine (C5H7N3O), respectively.

Scientists have yet to prove what this discovery will entail, but they speculate that Hajimoji can be used to and fight cancer and store digital data for centuries. But this study also opens the question: could Hajimoji be a hint of other forms of life?


(1) “What Is DNA? – Genetics Home Reference – NIH.” U.S. National Library of Medicine, National Institutes of Health, 19 Mar. 2019, ghr.nlm.nih.gov/primer/basics/dna.

(2) Warren, Matthew. “4 New DNA Letters Double Life’s Alphabet.” Scientific American, 22 Feb. 2019, http://www.scientificamerican.com/article/4-new-dna-letters-double-lifes-alphabet/.

(3) Zimmer, Carl. “DNA Gets a New – and Bigger – Genetic Alphabet.” The New York Times, The New York Times, 21 Feb. 2019, http://www.nytimes.com/2019/02/21/science/dna-hachimoji-genetic-alphabet.html?rref=collection%2Ftimestopic%2FChemistry&action=click&contentCollection=science®ion=stream&module=stream_unit&version=latest&contentPlacement=1&pgtype=collection.

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