DNA

DNA (Deoxyribonucleic acid) describes composition of aminoacids for every codon in genome. Structurally, DNA is double chain of Adenine, Thymine, Guanine and Cytosine (abbreviated as ATGC), where Adenine has always symmetrical bound with Thymine, and Cytosine with Guanine. Its function is analogous to digits or letters, allowing construction of more complex combinations from 4 basic symbols.

Ionizing radiation particles and acids/solvents can alter DNA or damage it, causing mutations. DNA can also get altered in process of reproduction.