Free Astronomy Magazine January-February 2023

7 ASTRO PUBLISHING dances in the non-biological mate- rial that makes up the surface of the planet we call home. The term “organic” does not mean “biological,” but “biological,” as well as our current understanding of how life evolves and works “at all,” necessarily means “organic.” The chemical logic to the significant car- bon content in ourselves applies here on Earth just as it would have in the ancient history of Mars. Cova- lent bonds to carbon are strong enough to persist across a wide range of environmental conditions, yet can enable molecules to flop, twist, and turn around those same bonds. When combined with oxy- gen, nitrogen, and hydrogen atoms, organic molecules can be fine-tuned like a lock and key, both in nature and in the laboratory, to make cer- tain kinds of interactions between pairs of molecules that also lead to environmentally persistent geome- tries. The C-G and A-T base pairs in DNA are, by far, the most famous ex- amples of this exquisite pairing of interactions between molecules, or intermolecular interactions , produc- ing a structure that can persist in water, frozen for millennia encased in amber, or even for one-million years in the tooth of a mammoth – a record-breaking age reported by scientists at the Centre for Palaeoge- netics in Stockholm back in 2021. In terms of the development of life on Earth, the strength of carbon bonds in small organic molecules does not come without some cost. In biology, this cost comes in the form T his video taken by NASA’s Perse- verance Mars rover shows some of the terrain the rover had to nego- tiate during its drive to the delta at Jezero Crater in April 2022. [NASA/JPL-Caltech] of energy needed to break and make these bonds to form other, more varied, or more complex mol- ecules. Nature’s solution has been two-fold. To solve part of the biosyn- thesis of complex organic molecules, Nature relies on the catalytic activity of some proteins, which contain within their complex folded struc- ture sites that can bind one or more molecules in a way that lowers the amount of energy required to per- form some chemical reaction. Just as a woodworker relies on a jig to hold wood in place or a surgeon relies on assistants to hold instruments during a procedure, proteins can bind and constrain molecules in such a way that a select chemical reaction be- comes possible with much greater probability and much lower energy than it would if those same mole- cules were simply floating around unconstrained in a laboratory flask or some primordial pool of water. To solve the complex issue of com- bining small molecules, such as amino acids, into larger molecules, such as proteins, Nature has instead chosen to forego making long chains of strong carbon-carbon bonds and instead relies on connect- ing amino and nucleic acids by using more reactive, but still stable, bonds involving the removal of one water molecule with the formation of each chemical bond – a chemical process known as a condensation reaction . In DNA, two nucleic acids are joined with the removal of one water and the formation of a phosphodiester bond between phosophorus and oxygen, each bound to the organic