The full name of DNA is Deoxyribonucleic Acid. It is a nucleic acid that carries the genetic information in the cell and is capable of self-replication and synthesis of RNA. The DNA contains the heredity code of a being. DNA consists of two long chains of nucleotides twisted into a double helix and joined by hydrogen bonds between the complementary bases adenine and thymine or cytosine and guanine. The sequence of nucleotides determines individual hereditary characteristics.
DNA carries the instructions for protein production. A protein's structure and function are determined by the sequence of its amino acids. This sequence is determined by the sequence of nucleotides in the DNA.
Protein synthesis begins with the separation of a DNA molecule into two strands. In a process called transcription, a new strand of nucleic acid called messenger RNA (mRNA) is produced. The mRNA carries the DNA's information to the ribosomes, parts of a cell where protein synthesis occurs. In a process called translation, amino acids are linked in a sequence controlled by mRNA to form a protein.
A gene is a sequence of DNA nucleotides that specifies the order of amino acids in a protein. Substituting one DNA nucleotide with another causes descendant cells or viruses to have the altered sequence. As a result, the sequence of amino acids in the protein may also be changed. Such a change in a DNA molecule is called a mutation.
In most cells, a DNA molecule replicates in the cell nucleus just before the cell divides. Replication begins with the separation of the two DNA chains. As the chains separate, each nucleotide attracts an associated nucleotide. The nucleotides join to form a new DNA molecule. The added nucleotides are linked by other bonds to form the side rail of the new molecule. This process continues until a new chain has formed alongside the old one.