Continuity:
* Universality: The genetic code is nearly universal across all living organisms. This means that the same codons (three-nucleotide sequences) code for the same amino acids in bacteria, plants, animals, and even viruses. This shared code is a fundamental piece of evidence for the common ancestry of all life.
* Conservation of codons: Most codons retain their meaning across species. This ensures that proteins with similar functions are produced in different organisms. For example, the codon "AUG" always codes for the amino acid methionine, which is the start signal for protein synthesis.
* Redundancy: The genetic code is degenerate, meaning that multiple codons can code for the same amino acid. This redundancy provides a buffer against mutations, as a change in a single nucleotide within a codon may not necessarily alter the resulting amino acid.
Change:
* Variation in mitochondrial DNA: Mitochondria, the powerhouses of cells, have their own DNA. While the mitochondrial genetic code is largely universal, some minor variations do exist in different organisms.
* Codon bias: While the genetic code is universal, there are differences in the frequency with which certain codons are used in different organisms. This bias can influence the efficiency of protein translation.
* Evolutionary changes: Over long evolutionary timescales, the genetic code has evolved in some organisms. For example, some species have slightly different codons for certain amino acids. These changes are usually subtle and do not significantly affect the overall function of the genetic code.
In summary:
The genetic code is a remarkable system that balances continuity with a small degree of change. The near-universal nature of the code reflects the shared ancestry of all life and ensures that proteins with similar functions are produced across species. However, the minor variations in the genetic code demonstrate its evolutionary flexibility and contribute to the diversity of life on Earth.
