. The genetic code is almost universal. The same codons are assigned to the same amino acids and to the same START and STOP signals in the vast majority of genes in animals, plants, and microorganisms

Exception to the Universal Code

The code that governs the translation of nucleotide information into amino acids is called the genetic code. The code is nearly universal, meaning that it is used by almost all organisms. However, there are some exceptions to this rule that have been found in mitochondrial codons and in some protozoans.

Mitochondrial Codons

Mitochondria are organelles found in eukaryotic cells that are responsible for generating ATP, the energy currency of the cell. Mitochondria have their own DNA, which is separate from the nuclear DNA of the cell. Mitochondrial DNA also has its own genetic code that differs slightly from the universal code. Some of the codons that code for amino acids in the universal code have different meanings in the mitochondrial code. For example, the codon UGA, which normally codes for the stop signal in the universal code, codes for the amino acid tryptophan in the mitochondrial code.

Protozoans

Protozoans are single-celled eukaryotic organisms that are found in many different environments. Some protozoans have been found to use non-standard genetic codes. For example, the ciliate protozoan Tetrahymena thermophila uses a different genetic code for one amino acid, glutamine. In this organism, the codon CUG codes for glutamine instead of leucine, as it does in the universal code.

Conclusion

While the genetic code is nearly universal, there are some exceptions to this rule that have been found in mitochondrial codons and in some protozoans. These exceptions demonstrate the flexibility of the genetic code and the ability of organisms to adapt to different environments and conditions.