The polyelectrolyte theory of the gene proposes that for a linear genetic biopolymer dissolved in water, such as DNA, to undergo Darwinian evolution anywhere in the universe, it must be a polyelectrolyte, a polymer containing repeating ionic charges. These charges maintain the uniform physical properties needed for Darwinian evolution, regardless of the information encoded in the genetic biopolymer. DNA is such a molecule. Regardless of its nucleic acid sequence, the negative charges on its backbone dominate the physical interactions of the molecule to such a degree that it maintains uniform physical properties such as its aqueous solubility and double-helix structure. The polyelectrolyte theory of the gene was proposed by Steven A. Benner and Daniel Hutter in 2002 and has largely remained a theoretical framework astrobiologists have used to think about how life may be detected beyond Earth. This idea was later linked by Benner to Erwin Schrödinger's view of the gene as an "aperiodic crystal" to make a robust, universally generalized concept of a genetic biopolymer—a biopolymer acting as a unit of inheritance in Darwinian evolution. Benner and others who built on his work have proposed methods for how to concentrate and identify genetic biopolymers on other planets and moons within the Solar System using electrophoresis, which uses an electric field to concentrate charged compounds. Although few have tested the polyelectrolyte theory of the gene, in 2019, lab experiments challenged the universality of this idea. This work was able to create non-electrolyte polymers capable of limited Darwinian evolution, but only up to a length of 72 nucleotides.
Physical structure of polyelectrolytes
A polyelectrolyte is a polymer with repeating electrostatically charged units. In the context of the polyelectrolyte theory of the gene, this polyelectrolyte is a biopolymer—a polymer derived from a living system—with a repeated ionically charged unit, similar to the genetic biopolymer in modern biology, DNA. Although RNA does not act as a genetic biopolymer archive in modern biology—except in the case of some viruses such as coronavirus and HIV—the RNA World hypothesis suggests that RNA may have preceded DNA as life's first genetic biopolymer. The nucleotide building blocks that make up DNA and RNA are connected by negatively charged phosphate groups. These phosphodiester linkages create the repeating negative charges on the molecule's backbone that give DNA and RNA their polyelectrolyte nature.
Polyelectrolytes in the context of genetic biopolymers To participate in Darwinian evolution, which can be described as "descent with modification", a unit of inheritance must be capable of imperfect replication to occasionally produce a new modified unit of inheritance, which must still be capable of being replicated. This imperfect replication leads to the variation on which Darwinian evolution can act. The polyelectrolyte theory of the gene attempts to understand modern biology's unit of inheritance, DNA, at a generalizable level. In 2002, Steven A. Benner and Daniel Hutter identified the repeated charges in DNA's phosphodiester linkages as crucial to its function as a genetic biopolymer. They proposed with the polyelectrolyte theory of the gene that repeated ionic charges—positive or negative—are a general requirement for all water-dissolved genetic biopolymers to undergo Darwinian evolution anywhere in the cosmos. This concept works in tandem with the view of the gene as an "aperiodic crystal" as proposed by Erwin Schrödinger in his 1944 book "What Is Life?". An aperiodic crystal, as Schrödinger describes it, has a discrete set of molecular building blocks in a non-repeating arrangement. DNA is an aperiodic crystal composed of discrete nucleobases (A, T, C, and G), which are arranged based on the information they encode, not in any repeated format. While this idea of an "aperiodic crystal" was not initially linked to the polyelectrolyte theory of the gene, Benner, in later work, connected the two.
Polyelectrolytes remain physically uniform regardless of the information encoded
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![Polyelectrolyte theory of the gene: Polyelectrolyte biopolymers tend towards linearity due to like-charge repulsive interactions on the backbone. DNA, for example, tends towards linearity due to repulsive interactions between the negative charges of its phosphodiester-linked backbone. Neutral biopolymers tend to fold and aggregate due to the lack of like-charge repulsive interactions.[2] Folding is generally a favorable process in neutral biopolymers because it creates favorable intramolecular interactions. For example, proteins tend to fold because this produces favorable interactions between the dipole moments of the backbone, between complementary amino acid side chains, and the exchange of unfavorable hydrophilic-hydrophobic interactions for favorable hydrophobic-hydrophobic interactions of the protein core.](https://upload.wikimedia.org/wikipedia/commons/thumb/b/b7/Polyelectrolyte_v_neutral_biopolymer.jpg/500px-Polyelectrolyte_v_neutral_biopolymer.jpg?utm_source=en.wikipedia.org&utm_campaign=parser&utm_content=thumbnail)
