Well Fancy That! - Answers

[bennevisplace]

QUESTION

"If you could somehow extract, uncoil and join together all (living) human DNA, and take it off into space, it would be long enough to encircle the Milky Way galaxy how many times?"

ANSWERS

Sepsur - 2 times, LeoPa - 5.93 times, bennevisplace see below.

ASSUMPTIONS

Uncoiled length of DNA per cell = 2 m (impressive supercoiling by DNA!)

Number of somatic cells in the human body = 37.2 trillion (somatic cells are human cells; in addition we have an even larger number of co-habiting bacterial cells).

World population = 7.8 billion (If this population was socially distanced standing 2 metres apart, India would not be big enough to contain everyone; Australia would).

1 light-year (a unit of distance used in cosmology) = 9.461 x 10^15 m

Diameter of Milky Way galaxy = 180,000 light-years (meaning light takes that many years to cross the galaxy; by comparison, light travels the diameter of the Earth in the click of a 1/30 sec photo. Alternatively, if you imagine the Milky Way galaxy shrunk to the size of the Earth, at the same scale our planet would be a sub-microscopic particle about the size of a single coronavirus).

CALCULATION

Total length of human DNA = 2 x 37.2 x 10^12 x 7.8 x 10^9 = 5.8032 x 10^23 m

= 61.338 million light-years

Circumference of Milky Way galaxy = pi x diameter = 3.14159 x 180,000 light-years

= 0.5655 million light-years

So the uncoiled length of all human DNA is enough to encircle the galaxy more than 100 times!

[AussieNeil Partner Administrator]

I'd love to be able to go for an orbit around the galaxy! Anyone care to calculate how long that would take at the speed of a Voyager probe?

On a more practical matter, what I find far more mind boggling, is how the 2m long dual strand DNA is so efficiently packed into a 6 micron - or one quarter of a thousandth of an inch in diameter nucleus, let alone how that DNA is unpacked, copied, error checked, corrected and repacked in an hour, at a rate of 50 nucleotides per second in multiple parallel processes during cell division.

Neil

[bennevisplace in reply to AussieNeil]

Re Voyager, here is an authoritative source voyager.jpl.nasa.gov/freque...

Neil you seem to be one of the first to contemplate a tour of the galaxy, although it's a fair bet that Elon Musk is making plans right now 😀 Our solar system, travelling at 828,000 km/hr, takes 230 million years to orbit the galaxy. Travelling at a leisurely 17,000 km/hr in Voyager 1, your best strategy would be to head in the contraflow direction, then you'd complete the tour in about 226 million years.

The inner galaxy of the cell is just as mind-boggling.

[bennevisplace in reply to AussieNeil]

Correction, I misremembered Voyager 1's speed, which is 17 km/ sec, i.e. 61,000 km/ hr, giving a counter-orbit time of about 213 m.y.

[LeoPa]

I googled that the milky way is elliptical, the shorter radius is 100 light years and the longer one is 150 light years. I made a mistake previously, now recalculated and came up with 68.4 times. Never mind, it's still a lot 😊

[bennevisplace in reply to LeoPa]

Thanks, happy to accept your answer LeoPa. I've seen various figures for the diameter, from 112,000 to 170-200,000 l.y., but apart from the fact the galaxy is not a circular disc and has spiral arms, I guess there are diverse ways to define what must be a very indistinct boundary.

Whatever, DNA is amazing stuff.