school energy&environment

Protein or DNA?

Today, proteins are formed following instructions given by DNA (deoxyribonucleic acid) which in turn is synthesized by specific enzymes that are proteins. So which came first, protein or DNA?
Nucleic acids (DNA and RNA) are made up by nucleotides which are molecules formed by one sugar with 5 carbon atoms, one phosphoric acid molecule and a nitro base.
Sugars with 5 atoms of carbon are ribose, which is found in the RNA (ribonucleic acid) and the deoxyribose in the DNA. Nitro bases are compounds with basic proprieties (which means that they can receive protons) that have nitro atoms and are: adenine, cytosine, guanine, thiamine, and uracil. We find the first four bases in the DNA, whereas in the RNA there are the first three and the … DNA contains the genetic information of all living organisms.
Proteins are large molecules made up by 20 small molecules called amino acids. All living organisms have the same 20 amino acids, but they are arranged in different ways and this determines the different function for each protein. Proteins perform all of an organisms’ vital functions, but the unique disposition of the amino acids within them is determined by a specific sequence of the nitro bases in the DNA. The RNA carries the message contained in the DNA to the cell area where protein is synthesized and will have to perform the synthesis as well.
So in a living being nucleic acids contain the information that is passed to the proteins that are in charge of many functions, including rebuilding these nucleic acids.
It seems rather unlikely that two molecules which are so important for life appeared at the same time, but on the other hand it seems absurd to have one without the other.
Some biologists among which Francis Crick and Leslie Orgel, each one of them on his own, assumed that there was a compound which could both duplicate without the help of proteins as well as catalyze each phase of the protein synthesis. This compound is supposed to be the RNA, because it is a simpler molecule compared to DNA and it is easier to synthesize.
Subsequently, many studies confirmed this supposition, including the discovery of enzymes made of RNA so they understood that not all chemical reactions are performed by proteins. They even succeeded to modify some RNA molecules with enzyme functions to make them able to bind nucleotides of RNA itself.
It still is not possible to prove for sure that the cells’ ancestor had an RNA which could synthesize proteins, as well as duplicate and modify itself; but it is even more important to be able to understand how this RNA was born.
We have already seen how adenine synthesis, one of the four nitrogen bases of DNA, was obtained in a lab experiment. Subsequently, other reactions among compounds that existed in this ancient atmosphere created also the other three nitrogen bases of nucleic acids.