Here's a small collection of my favourite analogies - for my thoughts about how to craft outstanding analogies, check out the chapter on analogies in my book Write Harder.
Special stretches of DNA (called Telomeres) are like...
VOICEOVER: Right at the ends of the chromosomes are special stretches of DNA called telomeres. They are known to play a crucial role protecting the ends of DNA.
PROFESSOR ELIZABETH BLACKBURN, MOLECULAR BIOLOGIST: So we kind of think of this like the tip at the end of the shoelace because if you don't have that tip then the end of your shoelace frays away very quickly, you know, your shoelace won't work properly if it doesn't have a tip.
What is a Telomere?, by the Smithsonian Channel, on Youtube. H/T Hanna Saltzman.