Picturing A Picogram. - Thebettereditor

Have you ever wondered what a “nano” really is? That prefix gets batted around a lot. It’s joined the always-lengthening list of words that were coined to show a precise meaning, but then were co-opted into generic use.

“Micro,” for example. It’s come to mean simply “very small.” Microcomputer, microprocessor, microbiology, and so on…even microwaves (not a precise description of their wavelength, but a description of a broad chunk of spectrum). The original Greek word “micro” does simply mean “small,” but as a prefix “micro” has a precise meaning: it’s one one-millionth of something, 0.000001, 10-6. Pretty small.

A “nano” of something is smaller still, only one one-billionth, .000000001, 10-9. A pico- of something is even smaller, one one-trillionth, .000000000001, or 10-12. If you’re interested in the etymology, pico- is a wholly created word, said to be derived from the Italian “piccolo” (small), and rarely used before it was codified as a metric standard unit in 1960.

Why have I chosen to cover picogram today? It’s a conceptual thing. The human brain has a difficult time conceiving of things that are either very large or very small. Can you really visualize a trillion? Mathematically, yes, because you can reduce it to 13 small digits on the page. But can you actually imagine what a trillion of something looks like? Not really. It’s the same with very small numbers. You can’t really picture the trillionth part of something. The brain can handle the math, but doesn’t cope well with the visualization. Most of us fail by the time we get to four orders of magnitude, let alone 12.

So when I recently came across a study that pinned something almost-visualizable to almost exactly one picogram (one trillionth of a gram), it seemed worth mention. What is that something?

One picogram is the average weight of the DNA in one cell of a hummingbird. That’s not the average weight of the whole cell. That’s the average weight of only the DNA in that one cell.  That’s small. Really small. But somehow, knowing that each hummingbird cell has just about one picogram of DNA somehow puts the measure into perspective. I still can’t completely visualize it, but I can start to get there: a hummingbird is real; one red blood cell from a hummingbird is something I can see under a microscope (100x was used in the study). It’s not much of a conceptual leap to picture the DNA in that single cell, and from that point to appreciate its tiny, tiny weight.

The actual journal article is here. A somewhat better plain-language summary is here (or here, if you have access).

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