An example of an analogy used in popular science writing:
"Xist RNA is very long, about 17,000 bases. Each amino acid is encoded by a block of three bases, so a 17,000-base RNA could theoretically code for a protein of over 5,700 amino acids. But when the Xist RNA sequence was examined, the longest run of amino acids was just under 300. … The 'problem' was that the Xist RNA was liberally scattered with sequences that don't code for amino acids, but which act as stop signals when protein chains are being built up. We can envisage this as being a little like trying to build a tall tower out of LEGO. It is perfectly straightforward until someone hands you one of those roof bricks that doesn't have any of the attachment nodes on the top. Once you insert this brick, your tower can't get any bigger.
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Some of the triplets on the messenger RNA don't have a match to any triplet on a tRNA. These triplets are known as stop signals. When the ribosome reads one of these, it can't fit a tRNA in place and the ribosome falls off the messenger RNA and the protein stops growing. These are the roofing LEGO bricks we met [above].
…in bacteria each ribosome can add amino acids at the rate of about 200 a second. It's probably not as fast as this in human cells, but it will still be about ten times faster than we could possibly stick two bricks together if we were making a LEGO tower. And don't forget that the ribosome isn't sticking together random LEGO bricks. It's as if we had to choose just two out of 20 different types of LEGO bricks (there are 20 different amino acids) and stick them on top of each other in exactly the right order every fraction of a second."
Nessa Carey (2015) Junk DNA. A journey through the dark matter of the genome. London: Icon Books Ltd.
Read examples of scientific analogies
The comparisons in speeds is an example of how the very large/small/fast/slow etc., can be compared with something everyday, quotidian, for rhetorical effect:
Read about quotidian comparisons
