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Essays from Our Physical World.

From atoms to DNA.

All living organisms on our planet are made of carbon, C, hydrogen, H, nitrogen, N, and oxygen, O.  Living organisms also contain phosphorous, P, sulfur, S, and other metals and nonmetals.  DNA contains carbon, hydrogen, oxygen, nitrogen and phosphorous. 
DNA is the chemical that carries the genetic code from one generation to the next. Other than a few very primitive organisms which use RNA, all living creatures use DNA to propagate their species. The DNA in a single cell may be composed of billions of atoms. These are arranged in a complex chain with four small nucleic acids (adenine, cytosine, guanine, and thymine) in carefully arranged ordered pairs. The order in which these four nucleic acids occur makes up the coded information needed to create a new individual member of the species.
What of the idea that life is situated around the atom rather than within?  Itís very logical to think that if a cell still contains life and itís broken down to molecules, that these molecules are the building blocks of life.  But a molecule isnít alive.  One would supposedly conclude that life should be situated around the molecule; a molecule is built by atoms, so life should be situated around atoms. 
This complex hypothesis yields an equivocal answer -- something along the lines of 'which came first, the chicken or the egg?'  Life depends upon molecules, and molecules are made up of atoms.  DNA consists of polymers of deoxyribonucleic acids.  Each individual nucleotide can be broken down into specific parts: the ribose sugar, the purine or pyrimidine base, and the three negatively charged phosphate groups that supply the energy for the creation of long chains of nucleotides. Each of these ingredients in turn can be broken down into functional groups, which can be further divided into the individual atoms - carbon, hydrogen, oxygen, nitrogen and phosphate.  However, if one tried starting from the other end and working up, a random mix of atoms - C, H, O, N, and P would not necessarily yield the molecules needed by a living organism.  So, though life can be considered at the atomic level, this consideration can only be truly approached within the considerations of what's happening at the molecular level.