The Universe of Discourse

A message to the aliens, part 18/23 (cell respiration and division)

Earlier articles: Introduction Common features Page 1 (numerals) Page 2 (arithmetic) Page 3 (exponents) Page 4 (algebra) Page 5 (geometry) Page 6 (chemistry) Page 7 (mass) Page 8 (time and space) Page 9 (physical units) Page 10 (temperature) Page 11 (solar system) Page 12 (Earth-Moon system) Page 13 (days, months, and years) Page 14 (terrain) Page 15 (human anatomy) Page 16 (vital statistics) Page 17 (DNA chemistry)

This is page 18 of the Cosmic Call message. An explanation follows.

The 10 digits are:

0

1

2

3

4

5

6

7

8

9

This page depicts the best way to fry eggs. The optimal fried egg is shown at left. Ha ha, just kidding. The left half of the page explains cellular respiration. The fried egg is actually a cell, with a DNA molecule in its nucleus. Will the aliens be familiar enough with the structure of DNA to recognize that the highly abbreviated picture of the DNA molecule is related to the nucleobases on the previous page? Perhaps, if their genetic biochemistry is similar to ours, but we really have no reason to think that it is.

The illustration of the DNA molecule is subtly wrong. It shows a symmetric molecule. In reality, one of the two grooves between the strands is about twice as big as the other, as shown at right.

The top formula says that C₆H₁₂O₆ and O₂ go into the cell; the bottom formula says that CO₂ comes out. (Energy comes out also; I wonder why this wasn't mentioned.) The notation for chemical compounds here is different from that used on page 14: there, O₂ was written as ; here it is written as (“2×O”).

The glyph near the left margin does not appear elsewhere, but I think it is supposed to mean “cell”. Supposing that is correct, the text at the bottom says that the number of cells in a man or woman is !!10^{13}!!. The number of cells in a human is not known, except very approximately, but !!10^{13}!! is probably the right order of magnitude. (A 2013 paper from Annals of Human Biology estimates !!3.72\cdot 10^{13}!!.)

Next to the cell is a ruler labeled !!10^{-5}!! meters, which is a typical size for a eukaryotic cell.

The illustration on the right of the page, annotated with the glyphs for the four nucleobases from the previous page , depicts the duplication of genetic material during cellular division. The DNA molecule splits down the middle like a zipper. The cell then constructs a new mate for each half of the zipper, and when it divides, each daughter cell gets one complete zipper.

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