DNA plays a major role in four main areas which include replication and heredity, transcription, mutation and recombination, and gene expression.
When a cell divides, the chromosomes containing the DNA strands must replicate, or make copies, of themselves so that both daughter cells receive the full set of genetic material. During replication, the DNA double helix unwinds, allowing each strand to act as a template for a newly synthesized complementary strand that forms a new double helix. The enzyme DNA polymerase assists in the process.
When a protein or RNA molecule needs to be produced, the first step is transcription. Like DNA replication, this begins with the transient formation of a single-stranded region. The single-stranded region then acts as the template for the polymerization of a complementary polynucleotide RNA molecule. Only one of the two strands of DNA is involved in transcription. This is called the template strand and the other strand is called the coding strand.
Even though it is very important for DNA to be duplicated with high accuracy for safe functioning, sometimes due to various reasons mutations occur which might be beneficial and required for evolution but also might cause genetic diseases in some cases. Mutations occur when segments of chromosomes swap and end up creating new sequences of genetic material. The new sequences produce new proteins which might be beneficial to the organism in evolving.
Even though every cell in the body consists the whole sequence of DNA, cells in different organs look and act differently. This is because only a part of DNA is used to make proteins of certain type. DNA plays a role as a traffic cop for the types of proteins a cell will make. It does this through interactions with proteins in the cells that cause only certain genes to express themselves.