The genetic code is a sequence of nucleotides on messenger RNA (mRNA) that dictates amino acid sequences in proteins. Comprising four nitrogenous bases (A, U, G, and C), the genetic code was deciphered through the contributions of scientists like Gamow, Nirenberg, and Khorana. The genetic code is triplet, commaless, non-overlapping, universal, degenerate, non-ambiguous, and collinear. With 64 possible codons, 61 code for amino acids, while three (UAA, UAG, and UGA) serve as termination codons. AUG is the initiation codon, coding for methionine. The genetic code's universality and specificity enable precise protein synthesis across all living organisms.
The wobble hypothesis, proposed by Crick (1966), explains the degeneracy of the genetic code. It states that the first two positions of a codon on mRNA pair precisely with the tRNA anticodon, while the third position allows "wobble" pairing. This hypothesis helps predict the minimum number of tRNAs required for protein synthesis. Genetic mutations occur during DNA replication, with error rates of 1 in 10–100 million bases. Point mutations, such as missense and nonsense mutations, can cause genetic diseases like sickle-cell disease and thalassemia. Frameshift mutations result from insertions or deletions of non-multiples of 3 nucleotide bases. While most mutations are harmful or neutral, some can provide benefits, enabling organisms to adapt to environmental stresses and evolve rapidly, as seen in RNA viruses.
Cephaleuros, a genus of algal pathogens, causes red rust and algal spot diseases in vascular plants. Recent studies have revealed key features of its chloroplast genomes, including large size (216-408 kbp), circular structure, elevated evolution rates, strong rearrangement dynamics, and an alternative genetic code. These findings provide valuable insights into the evolution and genetics of Cephaleuros.
C-to-U RNA editing is a promising technique for treating genetic diseases caused by point mutations. This approach involves converting cytidine (C) to uridine (U) in RNA molecules, leading to nonsynonymous changes in coding regions. Although less common than A-to-I editing, C-to-U editing has been found in hundreds to thousands of coding sites in humans. This review explores physiological and artificial approaches for C-to-U RNA editing, highlighting its potential as a therapeutic technique for genetic disorders.
The genetic code is a fundamental concept in molecular biology, dictating the translation of genetic information into proteins. Its universality, degeneracy, and specificity enable precise protein synthesis, while mutations can lead to genetic disorders. Understanding the genetic code has revolutionized our knowledge of life and paved the way for advances in genetic engineering and gene therapy.
REFERENCES
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NIRENBERG, M.W. (1963). The genetic code. Scientific American, 208(3): 80-95.
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FANG, J., LIU, B., LIU, G., VERBRUGGEN, H., AND ZHU, H. (2021). Six newly sequenced chloroplast genomes from Trentepohliales: the inflated genomes, alternative genetic code, and dynamic evolution. Frontiers in Plant Science, 12: 780054.
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BHAKTA, S. AND TSUKAHARA, T. (2022). C-to-U RNA editing: a site-directed RNA editing tool for restoration of genetic code. Genes, 13(9): 1636.
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