Academic journal article Perspectives on Science and Christian Faith

Biological Information, Molecular Structure, and the Origins Debate

Academic journal article Perspectives on Science and Christian Faith

Biological Information, Molecular Structure, and the Origins Debate

Article excerpt

A traveler is checking in for a flight and her bags are slightly over the weight limit. Without hesitating, she pulls out her iPod. It is very heavy, she explains to the check-in agent, since it contains thousands of songs. She deletes most of the music, repacks the iPod, and reweighs the bags--which are now well within the weight limits.

Or consider a kindergarten student, learning to write letters. He writes a whole page of A's with no trouble. Next he wants to practice writing the letter G. But after a few G's are written, they seem to want to fold onto each other, as though he were writing on the sticky side of a piece of tape. Each new G he manages to add contributes a new wrinkle or fold, until eventually he gives up and decides to practice writing a less troublesome letter.

When we laugh at these two impossible stories, it reveals how deeply, almost reflexively, we tend to feel that information should be distinct from physical properties. At least in terms of computer code or printed text, we expect that similar devices containing different information will have similar physical properties. By contrast, different devices may contain the same information in spite of their dramatically different physical properties (for example, the printed and online versions of this article).

But biological information is quite different. This article will show that there is a fundamental difference between biological information and abstract information such as computer code or text: the biological information cannot be separated from its structure. The structure and reactivity of biomolecules can give rise to new information without the direct input of an intelligent agent. Thus we need to be careful when analogies from the world of computers or literature are applied to biological information. This is important in terms of the debate on the origin of life.

The Information-Structure Duality of Biomolecules

Discussion of biological information is often limited to the DNA (or RNA/protein) sequence, which superficially looks much like the kinds of abstract information we are familiar with. When the human genome sequence was published, biology was said to have entered an information age. Stephen Meyer begins his book Signature in the Cell by quoting from sources as diverse as Bill Gates and Richard Dawkins who find that "the machine code of the genes is uncannily computer-like." Meyer's next question is highly pertinent: "If this is true, how did the information in DNA arise?" (1)

While I enjoyed reading much of Signature in the Cell, I felt that the analogy between DNA and abstract information was taken too far. The issue is that biological information is not abstract: it is always mediated and interpreted by physical interactions. While studying the chemistry and biochemistry of oligonucleotides (short sequences of DNA, RNA, and their chemically synthesized analogues), I have often come face-to-face with the frustration that can be caused by forgetting how tightly information and structure are intertwined.

Some oligonucleotide sequences can be manipulated easily enough, such as the letters within an abstract line of text. But other sequences have repeatedly reminded me that a DNA sequence is not just an abstract line of text. For example, a famous sequence called the Dickerson-Drew dodecamer (5'-CGCGAATTCGCG) (2) can bind another copy of itself by classic Watson-Crick base pairing (A-T and G-C pairs, figure 1a). But under different conditions, it will instead fold back on itself, forming into a "hairpin" structure while still making use of Watson-Crick base pairs (figure 1b). Various factors, including chemical modifications, can favor one structure over the other. (3) While the sequence information is the same, the two structures respond very differently in experiments (i.e., they exert different functions).

Some of my colleagues have made various chemically modified analogues of the sequence GGTTGGTGTGGTTGG. …

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