Genetic code

The genetic code is a set of rules that determines how the information stored in DNA is translated into the amino acid sequence of proteins. It is essentially a mapping between nucleotide triplets, called codons, and the corresponding amino acids or other functional signals. The genetic code is universal, meaning that the same codons encode the same amino acids across all living organisms. Here are some key properties of the genetic code:

1. Triplet Nature: The genetic code is triplet, meaning that each codon consists of three nucleotides. There are 64 possible codons (4 nucleotides raised to the power of 3), and these codons encode the 20 standard amino acids, along with start and stop signals.

2. Degeneracy: Degeneracy refers to the redundancy in the genetic code, where multiple codons can code for the same amino acid. Most amino acids are encoded by more than one codon, with the exception of methionine and tryptophan, which each have a single codon. This redundancy allows for some tolerance to mutations in the DNA sequence, as certain changes may not affect the amino acid sequence of the resulting protein.

3. Start and Stop Codons: The genetic code includes specific codons that serve as start and stop signals for protein synthesis. The start codon, AUG (encoding methionine), initiates translation and marks the beginning of the protein coding sequence. There are three stop codons (UAA, UAG, and UGA) that signal the termination of translation and the completion of the protein.

4. Universal: The genetic code is nearly universal, meaning that the same codons specify the same amino acids in all known organisms, from bacteria to humans. This universality reflects the common ancestry of all life on Earth and provides a fundamental basis for molecular biology and evolutionary studies.

5. Non-Overlapping and Commaless: The genetic code is non-overlapping, meaning that each nucleotide is part of only one codon and is not shared between adjacent codons. Additionally, there are no gaps or punctuation between codons (hence "commaless"), ensuring that the reading frame is maintained during translation.

6. Conservation and Evolution: Despite its universality, the genetic code is not entirely static and can evolve over time. While the core genetic code is highly conserved across organisms, certain variations and deviations from the standard code have been observed in specific taxa or organelles (e.g., mitochondrial DNA). These variations can result in differences in codon usage and translation efficiency.

7. Wobble Base Pairing: The third position of the codon (the "wobble" position) exhibits more flexibility in base pairing, allowing for non-standard base pairing between the codon and anticodon during translation. This flexibility contributes to the degeneracy of the genetic code and allows for efficient and accurate translation despite minor variations in the nucleotide sequence.

Here's a chart representing the standard genetic code, showing the correspondence between codons (triplet nucleotide sequences) and the encoded amino acids:

| U | C | A | G | ------------------ | U | UUU | Phenylalanine (Phe) | UCU | Serine (Ser) | UAU | Tyrosine (Tyr) | UGU | Cysteine (Cys) | | | UUC | Phenylalanine (Phe) | UCC | Serine (Ser) | UAC | Tyrosine (Tyr) | UGC | Cysteine (Cys) | | | UUA | Leucine (Leu) | UCA | Serine (Ser) | UAA | Stop | UGA | Stop | | | UUG | Leucine (Leu) | UCG | Serine (Ser) | UAG | Stop | UGG | Tryptophan (Trp) | ------------------ | C | CUU | Leucine (Leu) | CCU | Proline (Pro) | CAU | Histidine (His) | CGU | Arginine (Arg) | | | CUC | Leucine (Leu) | CCC | Proline (Pro) | CAC | Histidine (His) | CGC | Arginine (Arg) | | | CUA | Leucine (Leu) | CCA | Proline (Pro) | CAA | Glutamine (Gln) | CGA | Arginine (Arg) | | | CUG | Leucine (Leu) | CCG | Proline (Pro) | CAG | Glutamine (Gln) | CGG | Arginine (Arg) | ------------------ | A | AUU | Isoleucine (Ile) | ACU | Threonine (Thr)| AAU | Asparagine (Asn) | AGU | Serine (Ser) | | | AUC | Isoleucine (Ile) | ACC | Threonine (Thr)| AAC | Asparagine (Asn) | AGC | Serine (Ser) | | | AUA | Isoleucine (Ile) | ACA | Threonine (Thr)| AAA | Lysine (Lys) | AGA | Arginine (Arg) | | | AUG | Methionine (Met) | ACG | Threonine (Thr)| AAG | Lysine (Lys) | AGG | Arginine (Arg) | ------------------ | G | GUU | Valine (Val) | GCU | Alanine (Ala) | GAU | Aspartic Acid (Asp) | GGU | Glycine (Gly) | | | GUC | Valine (Val) | GCC | Alanine (Ala) | GAC | Aspartic Acid (Asp) | GGC | Glycine (Gly) | | | GUA | Valine (Val) | GCA | Alanine (Ala) | GAA | Glutamic Acid (Glu) | GGA | Glycine (Gly) | | | GUG | Valine (Val) | GCG | Alanine (Ala) | GAG | Glutamic Acid (Glu) | GGG | Glycine (

Note:

• "Stop" indicates the termination of translation.
• AUG serves as both the start codon (initiating translation) and codes for Methionine (Met).

Overall, the genetic code is a remarkable and highly conserved system that underlies the flow of genetic information from DNA to protein in all living organisms. Its properties of degeneracy, universality, and precision provide the foundation for understanding gene expression, protein synthesis, and the molecular basis of life.