Functional Information in DNA Sequences
The biological importance of DNA depends upon particular sequences performing useful functions. Some sequences specify molecular products, while others help regulate when and where those products are produced.
The Investigative Question
What makes one DNA sequence biologically functional while another sequence may have little or no effect?
What We Observe
Not every possible DNA sequence performs the same biological role.
Some DNA sequences contribute to proteins. Others specify functional RNA molecules. Still others participate in regulating gene expression by providing promoters, enhancers, binding sites, and other regulatory elements.
Function therefore depends in part upon the particular ordering of nucleotides and upon the cellular context in which that sequence occurs.
Scientific Background
A protein-coding DNA sequence can ultimately influence the amino-acid sequence of a protein. Regulatory DNA operates differently. Particular sequences can be recognized by transcription factors and other molecular machinery that influence whether nearby genes are expressed.
Modern genomics has revealed a complicated landscape containing protein-coding genes, noncoding RNAs, promoters, enhancers, silencers, insulators, and other candidate regulatory elements.
The same genome can consequently support very different patterns of activity in different cell types.
Why It Matters
Biological information cannot be understood simply by counting the number of DNA bases in a genome.
The sequence, location, interactions, and cellular context of genomic elements all matter. A liver cell and a neuron can contain essentially the same genome while using very different portions of it.
This means that biological organization involves both stored sequence information and systems that determine how that information is used.
What Is Known
Experiments have identified many DNA sequences with demonstrated or candidate roles in producing RNAs and proteins or regulating gene activity.
The ENCODE Project has mapped large numbers of candidate cis-regulatory elements and has documented that genomic activity differs among cell types and tissues.
Mutations in coding or regulatory sequences can alter biological function, although many sequence changes have little or no detectable effect.
What Is Proposed
Functional genomic sequences can arise and change through mutation, duplication, recombination, transposable elements, natural selection, genetic drift, and other evolutionary processes.
Existing sequences can also acquire new functions or regulatory relationships over evolutionary time.
What Remains Uncertain
Scientists continue to investigate the functions of large portions of complex genomes. Detecting biochemical activity does not automatically demonstrate that a sequence performs an important organism-level function.
Claims about the amount of a genome that is functional therefore depend upon how function is defined and measured.
The evolutionary histories of many regulatory elements also remain subjects of continuing research.
Key Numbers
ENCODE 2020 reported a registry of 926,535 candidate cis-regulatory elements in the human genome, covering about 7.9% of the genome under its specified criteria.
Design Relevance
Functional DNA sequences are relevant to Intelligent Design because their biological effects depend upon particular arrangements of nucleotides operating within larger cellular systems.
Design advocates argue that functionally significant sequence arrangements resemble other forms of specified information known to arise from intelligence.
That argument must be evaluated alongside demonstrated evolutionary mechanisms capable of modifying, preserving, duplicating, and repurposing genetic sequences.
Assessment
The genome contains far more than a simple list of protein recipes. It includes coding sequences, functional RNAs, regulatory elements, and numerous interactions controlling how genetic information is used.
This richer picture strengthens the importance of investigating biological information, but it also cautions against simplistic claims that every nucleotide must have a specific purpose.