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DNA is commonly referred to as a language. For example, I can see that DNA is made up of nucleotides (ATGC) that form meaningful units (genes, chromosomes, etc). DNA gets transmitted to future generations, it can be 'listened to' by ribosomes to produce proteins and other building blocks, so one could argue that there is communication going on.
In what ways does DNA actually follow definitions that are common to spoken/sign language, and in what ways does it differ?
DNA is a physical code. It would be possible to encode a natural human language in it just like we can encode English in Morse code. But the natural DNA in our cells does not encode a language, it is not literature. There is no symbolic meaning of the DNA in our genomes. It is closer to the non-linguistic diagrams telling you how to assemble your Ikea furniture or Lego set.
DNA has very little in common with human languages. But it could be said it is a kind of programming language. It isn't either really, it misses a lot of essential features.
A piece of DNA sequence called "gene" is encoding amino-acid sequence of proteins, those in turn act as enzymes and structural elements of living cells. In this sense DNA is an alphabet/script or a code/cypher.
The other, relatively recently discovered feature of DNA is controling of gene expression - a protein or other molecule may activate or deactivate a gene by binding with DNA - this close equivalent of conditionals allows us to call DNA a programming language, albeit a very limited one.
A sequence of code (signals or text) is not a language. A language is a set of rules for creating and interpreting (meaningful) expressions of information which expressions are composed of basic coding elements that denote basic concepts. The rules for expressing and interpreting information in natural language code can only be derived from examples of text or spoken stories. Only artificial languages have explicit definitions in rules and a set of basic coding elements for concepts. The codons in DNA are the basic coding elements and they denote amino acids as basic concepts. The expressed information is information about how to build functional proteins and higher level functional assemblies. Most likely there are rules for recognizing or creating new high quality DNA code that determine the fabrication of functioning proteins etc. Similar to natural languages, such rules for a bio-language can only be derived from examples of DNA-code. We should take into account that DNA-code not only denote amino acids or determine their sequence in proteins, but also determine how molecular machines and organisms are build. We know the codons, thus, if we would know those rules, then we would know for a newly designed functional protein or molecular machine how its construction should be encoded in DNA code. And more, we should be able to read and write fabrication instructions for 'body plans' for bacteria, plants, animal- and human bodies (provided the ribosomes would accept our code).
A functional bio-language system requires not only rules and code, but also a producer of new code (that can copy or invent by applying the rules) and an interpreter that can also apply the rules and that can do meaningful things with it. In the bio-language case the interpreting machines are the ribosomes, which are like robots that can use the code as instruction for building components (such as tRNA and proteins) as well as machines and organisms that are guided to become assembled from those components.
This bio-language system has similarities with language systems that guide complexes of robots, but they are more than guiding robots to make assemblies, because they also guide the building of the robots themselves and they guide the robots that copy themselves. The only missing component is organisms that invent new machines and code their body plans.
My conclusion: DNA is not a language, but DNA code is written in a bio-language.
