| | On the correspondence between amino acids and their genetic codes Amino acids are coded by genetic codes. There is a correspondence between amino acids and genetic codes. There are 22 types of amino acids. Together with start and stop signals, there are 24 items to be coded. With 4 RNA codes, C, U, A, G, it takes 3 codes to determine one amino acid. The total coding combination is 4^3 = 64, which is bigger than 24. There is some redundancy. We will discuss some patterns of distribution of such redundancy. First, all 64 possibilities of genetic codes are utilized in nature. This is consistent with maximum entropy principle. Second, the distribution of the redundancy is not very uniform. Some amino acids, such as leucine, have six representations. Others, such as tryptophan, have only one representation. There could be many reasons for this difference. One might be the frequencies of different amino acids. For example, leucine has high frequency while tryptophan has low frequency. Third, the differences of genetic codes for the same amino acid usually occur at the third code. For example, alanine is represented by GCU, GCC, GCA, GCG. The first two codes are identical. The difference occurs at the third code. The third position is often called the wobble position. Probably the work at the end is usually shabbier, generating greater probabilities of mistake. Fourth, when an amino acid is coded by two genetic codes, the last position is A and G, or C and U. They belong to the same group, either purine or pyrimidine. For example, serine is coded with AGU and AGC. Both U and C are pyrimidines. I guess when mistakes were made, it is easier to grab the same type of molecules. Fifth, positions are usually taken by pyrimidines first. Let me use some examples to explain this pattern. Isoleucine has three codes, AUU,AUC, AUA. The third, unpaired position is A, a purine. Arginine has six codes, CGU, CGC, CGA, CGG, AGA, AGG. The first four codes form one whole group. In the last two codes, the final positions are A and G, both purines. I guess pyrimidines are cheaper. They are taken first. It is great that the correspondence between amino acids and their genetic codes exhibits so many patterns. Are there more patterns? Reference: Codon tables https://en.wikipedia.org/wiki/DNA_and_RNA_codon_tables#Translation_table_1 https://www.reddit.com/r/askscience/comments/1ft19n/does_the_fact_that_some_amino_acids_have_multiple/ https://www.quora.com/Why-do-some-amino-acids-have-more-than-one-codon-for-their-recognition?share=1
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