Genetic Code

Genetic Code is a set of rules used by living cells to translate information encoded within genetic material into proteins. Translation is accomplished by the ribosome, which links amino acids in an order specified by messenger RNA (mRNA), using transfer RNA (tRNA) molecules to carry amino acids and to read the mRNA three nucleotides at a time. The genetic code is highly similar among all organisms and can be expressed in a simple table with 64 entries.

Overview

The code defines how sequences of nucleotide triplets, called codons, specify which amino acid will be added next during protein synthesis. With some exceptions, a three-nucleotide codon in a nucleic acid sequence specifies a single amino acid. The vast majority of genes are encoded with a single scheme (often referred to as the standard or canonical code). That scheme is often referred to as the canonical or standard genetic code, or simply the genetic code, though variant codes (such as in human mitochondria) exist.

Codons

In the genetic code, a codon is a sequence of three DNA or RNA nucleotides that corresponds with a specific amino acid or stop signal during protein synthesis. DNA and RNA molecules are written in a language of four nucleotides; meanwhile, the language of proteins includes 20 amino acids. Codons provide the key that allows these two languages to be translated into each other. Each codon corresponds to a single amino acid (or stop signal), and the full set of codons is called the genetic code. The genetic code includes 64 possible permutations, or combinations, of three-letter nucleotide sequences that can be made from the four nucleotides.

Genetic Code Properties

The genetic code has a number of important properties. These include:

• Redundancy: Most amino acids are encoded by more than one codon. Therefore, the genetic code is said to be redundant, or degenerate. This is seen as an evolutionary advantage, as it reduces the impact of mutations.
• Unambiguous: Each codon specifies for only one amino acid (or one stop codon), making the genetic code unambiguous.
• Non-overlapping: Codons do not overlap, and are read from a fixed starting point.
• Universal: With very few exceptions, the genetic code is universal, with all life on Earth using the same code.

See Also

• DNA
• RNA
• Protein Synthesis
• Amino Acids
• Codon
• Mutation

Genetic Code Resources
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