The Letters that Code for Our LIves

The Alphabet of Life by Marissa Cevallos, an article in the ScienceNews magazine, sets off to search for clues to the origin of genetic codes, or the codes that govern our lives. Surprisingly, only four letters make up the overall sequence of the genetic code. According to the research, these letters (A, C, G and T) also known as nucleotides "combine to spell out the more than five dozen three-letter words that encrypt the information needed to make all the cells int he human body, and any other body as well." The sequence of nucleotides  are responsible for coding the "instructions for making proteins." Unfortunately, the quest to discover how life's code came to be becomes a difficult one when there is no way to replicate life's earliest days, so scientists are stuck with only one version (us humans) to study in order to decipher the possible origin of the fundamental codes. The author of the article interestingly compares sets of codons to the concept of synonyms. She mentions this in the article because often times, three or four codons will code for the same amino acid. This feature was thought to have been developed in order to protect cells from making errors: for example, if RNA's CGA mutates to CGU, the cell will still code for the same amino acid despite the mistake it has made earlier. Tsvi Tlusty of Weizman Institute of Science in Rehovot, Isarael believes that the genetic code does its job so well because it has adapted under evolutionary pressure, much like Darwin's theory of natural selection. According to Tlusty, the three possible pressure that shaped the current genetic code includes the " inability of typos to be disastrous, the language (codes) must spell words with diverse meanings and the language shouldn't take a lot of resources to write."


E. Koonin noticed that changing the last letter in a set of triplet codons does not drastically change the overall amino acid. Therefore, he concluded that "early genetic code relied on only the first two of its three letters." Through experimentation, Koonin's team found that minimizing errors was the thing that caused the genetic code's development - "when having more than 16 amino acids was advantageous, the code started to use the third letter."


In order to determine which amino acids came first, we have to turn over to the chemistry side of the puzzle. In his famous spark tube experiment, Stanley Miller created a handful of life's amino acids by electrically zapping together hydrogen, water, methane and ammonia gases. Surprisingly, five amino acids that were created in this experiment were found within meteorites - glycine, alanine, aspartic acid, glutamic acid and valine. Each of the codons that code of these amino acids starts with a letter G, suggesting that G may have been the first letter to code for an amino acid. Another scientists believed that the first amino acids were the ones with a natural chemical attraction to RNA.


In another case the researchers at the Georgia Institute of Technology in Atlanta are trying to approach the problem by going back into time. Biochemist Loren Williams has turn to look at ribosomes, the factory which is essential in generating proteins. Williams has found that some of the oldest RNAs are situated inside the ribosome due to its densely connected nature with other RNAs. According to his findings, Williams argues that the oldest protein situated inside the protein means that these amino acids may have been first to join the code. In another approach, aerobiologist Eric Gaucher is currently comparing individual protein in different living organisms to try to estimate a likely protein ancestor.

Despite the exhaustive amount of  research that have been done concerning this area of interest, genetic code still holds many, puzzling mysteries and secrets for biologists all around the globe, proving that a task like this is not an all easy to accomplish. In my opinion, the quest to search for the origins of the genetic code holds a lot of importance in understanding how proteins, the essential part of all living organisms, function at a deeper level. Studying the past may lead scientists to discover amazing things about protein for future generations. Sometimes it's necessary to take one step back in order to be able to move three steps forward.