Genetic code and its properties
The genetic code is a system for recording genetic information about the sequence of amino acids in proteins in the form of a sequence of nucleotides in DNA or RNA.
Each amino acid of the protein corresponds to a sequence of three DNA nucleotides located one after another – a triplet.
Each triplet of nucleotides encodes a specific amino acid that will be inserted into the polypeptide chain.
As you know, DNA can contain four nitrogenous bases: adenine (A), guanine (G), thymine (T), and cytosine (C). The number of combinations from 4 to 3 is 43 = 64, that is, DNA can encode 64 amino acids. However, only 20 amino acids are encoded in total.
It turned out that many amino acids correspond to not one, but several codons. It is assumed that this property of the genetic code (degeneracy) increases the reliability of storage and transmission of genetic information during cell division.
Example: the amino acid alanine corresponds to 4 triplets – CHA, CHG, CHT and CHC. It turns out that an accidental error in the third nucleotide of the codon cannot lead to changes in the structure of the protein – it will still be an alanine codon.
To date, a map of the genetic code has been compiled, that is, it is known which triplets in DNA correspond to one or another of the 20 amino acids that make up proteins.
Since the DNA molecule contains hundreds of genes, it necessarily includes triplets – stop codons, which are “punctuation marks” and denote the beginning or end of a particular gene.
Properties of the genetic code:
1.the code is triplet. One amino acid is encoded by three nucleotides.
2. The code is universal. All living organisms (from bacteria to humans) use a single genetic code.
3. The code is degenerate. One amino acid is encoded by more than one triplet.
4. The code is unambiguous. Each triplet corresponds to only one amino acid.
5. The code does not overlap. One nucleotide cannot be part of several codons in the mRNA chain.
The sequence of nucleotides in a DNA molecule determines its specificity, as well as the specificity of the body proteins that are encoded by this sequence. These sequences are individual for each type of organism and for individual individuals of the species.