expression of long non-coding RNA molecules is like producing sawdust when cutting branches into logs

An example of an analogy used popular science writing to explain a technical metaphor:

"Hardcore junk aficionados might claim that if a sequence is expressed as a long non-coding RNA molecule then that molecule is being expressed for a reason. Other scientists are much more sceptical, positing that the expression of the long non-coding RNAs is essentially what we call a bystander event. This means that the long non-coding RNAs are expressed, but just as a by-product of switching on a 'proper' gene. To understand what's meant by a bystander event, let's imagine we are cutting up tree branches with a chainsaw. The major aim of our activity is to create logs that we can use to build a cabin or to provide fuel for a stove. We aren't trying to create woodchips or sawdust, but this happens anyway as a result of the chainsaw function. …

The sceptics claim that the different long non-coding RNAs are detected simply because various brain regions switch on different classical protein-coding genes. In our chainsaw analogy this is equivalent to getting different woodchips depending on whether we are sawing up oak branches or pine."

Nessa Carey (2015) Junk DNA. A journey through the dark matter of the genome. London: Icon Books Ltd.

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Many examples of science analogies are listed in 'Creative comparisons: Making science familiar through language. An illustrative catalogue of figurative comparisons and analogies for science concepts'. Free Download.