DNA and the Storage of Biological Information
DNA is the principal hereditary material of cellular life. Its sequence of four nucleotide bases stores information that can be copied, inherited, and used by cells.
The Investigative Question
In what sense does DNA store biological information, and how is that information used by living cells?
What We Observe
DNA is chemically a long polymer constructed from four kinds of nucleotide bases: adenine, thymine, guanine, and cytosine.
The remarkable feature of DNA is not merely the presence of these chemicals. Their order matters.
Different sequences carry different hereditary information. Cells copy those sequences when DNA is replicated, and particular portions of DNA can be read to produce RNA and, through additional cellular machinery, proteins.
Scientific Background
DNA normally consists of two complementary strands. The bases pair in a regular way: adenine with thymine and guanine with cytosine. Because each strand specifies its complement, the molecule can serve as a template during replication.
The genetic information itself is carried in the linear sequence of nucleotides. Changing that sequence can alter the RNA or protein product associated with a gene, affect regulation, or sometimes have little detectable effect.
DNA therefore combines a chemically regular backbone with a variable sequence capable of carrying hereditary information.
Why It Matters
This distinction between the chemical structure of DNA and the sequence carried by that structure is important.
A DNA molecule must obey chemistry, but chemistry permits an enormous number of possible nucleotide sequences. Biological function depends upon particular sequences and upon cellular systems capable of copying and interpreting them.
The origin of biological information therefore involves more than explaining why nucleotides can form DNA. It also involves explaining the origin of sequences that participate in useful biological functions.
What Is Known
DNA is the hereditary material of cellular organisms. Genetic information is carried in its nucleotide sequence.
Complementary base pairing provides a physical mechanism by which DNA sequences can be copied. Cells also contain machinery that recognizes particular DNA sequences and uses selected portions of the genome in gene expression.
Mutations can change DNA sequences, and those changes can be inherited when they occur in appropriate cells and are successfully replicated.
What Is Proposed
Evolutionary biology explains existing DNA sequences as products of mutation, recombination, natural selection, genetic drift, common descent, and other processes acting over generations.
Origin-of-life research asks an earlier question: how the first hereditary polymers and functionally useful sequences arose before a mature biological evolutionary system existed.
What Remains Uncertain
There is no dispute that DNA carries hereditary information in modern cells. The deeper historical question is how sequence-based heredity first arose.
The earliest life may not have used DNA at all. Many origin models propose an earlier RNA-based stage, with DNA becoming the principal hereditary material later.
We therefore should not assume that the first biological information was stored in DNA in the same way that information is stored in modern organisms.
Key Numbers
DNA uses four principal nucleotide bases: adenine (A), thymine (T), guanine (G), and cytosine (C).
Design Relevance
DNA is relevant to Intelligent Design because biological function depends not merely upon the existence of nucleotides but upon their arrangement into useful sequences.
Design advocates argue that sequence-specific functional information is the kind of feature that warrants consideration of intelligent causation.
The investigation must go farther than noting that DNA contains information. We must ask how functional sequences can arise through natural processes, what evolutionary mechanisms can accomplish once heredity exists, and how the first information-bearing hereditary system originated.
Assessment
Calling DNA an information-bearing molecule is ordinary molecular biology, not terminology invented by Intelligent Design.
But the existence of information does not by itself establish its origin. The important question is how sequence-dependent biological function arose and became incorporated into a reproducible hereditary system.