The Inspirational Design of DNA

This entry is a summary of The Inspirational Design of DNA, by Fazale R. Rana, PhD, published in Chapter 3 of Building Bridges, 2018 by Reasons to Believe.

DNA design is elegant, ingenious, and optimally designed for its role in the cell as a molecular-scale information storage system.  Biochemists believe that DNA approaches the theoretical maximum in terms of its digital storage capacity.

There are several key structural features of DNA that are responsible for its optimal data storage properties. Emerging data indicates that the components that make up the nucleotides appear to have been chosen carefully with every detail of DNA’s structure critically factored into this molecule information-storage role.  The components must give the DNA maximum stability while still allowing for protein binding to occur.

Phosphate is perfectly suited to form the stable backbone. Phosphate can form bonds with two sugars at the same time to bridge two nucleotides, while still maintaining a negative charge.  This negative charge imparts the DNA backbone with stability that prevents reactive water molecules from cleaving it.  The charge also serves as a protein binding site.  Both phosphite and sulfate (chemical analogs to phosphate) can form two bonds, but would do so without the necessary negative charge remaining. Arsenate (also a chemical analog) is not able to form bonds with organic materials.

The specific nature of the phosphate to sugar bonds is also optimized. The 5’ to 3’ phosphodiester linkage is a maximally stable bond; stability being one of the requirements to effectively store information. The sugar itself, deoxyribose (which lacks an OH group on the #2 carbon), also provides stability.  Ribose (the sugar in RNA), however, has this #2 OH group, which can catalyze the cleavage of the backbone. While DNA needs to be stable to store information, RNA needs to possess a certain measure of instability to keep extra proteins from cluttering up the cell.  The use of thymine (instead of uracil) in DNA, along with the antiparallel arrangement of the nucleotide strands both lead to the increased stability of DNA over RNA.

Research has shown that deoxyribose is the only sugar that could fulfill the role it does in DNA. When other sugars instead of deoxyribose are used, the DNA does not have all the properties necessary to operate in the cell.  Some of the analogs don’t form a double helix, in others the interaction between the nucleotide strands is too strong or too weak.  Still others can assume multiple structural conformations – which keeps the cells machinery from operating on the DNA as it should.

The nucleobases adenine, guanine, cytosine, thymine, and uracil appear to be the best possible choices as well. This set of nucleobases display ideal photophysical properties; minimizing the damage caused by ultraviolet radiation by absorbing light at exactly the same wavelengths that are most effectively shielded by ozone! Also, the chemical structure of these nucleobases cause the UV radiation to be radiated away after absorption, limiting the damage.

One kilogram of DNA can store all the digital data that currently exists. This exquisite optimization of DNA’s structure indicates that it is not the outworking of a historically contingent evolutionary process; instead extreme optimization points to a creator. Computer scientists and molecular biologists have come to realize that the cells machinery, which manipulates DNA, literally functions like a computer system at its most basic level of operation. How could humans have designed a system that operates exactly like the information computing system that operates inside a cell?  The most rational answer is that since we were created by God, we think in a similar way as our creator.