DNA, or deoxyribonucleic acid, is a complex molecule that contains the genetic instructions necessary for life. Although it was discovered over 70 years ago, scientists are still unraveling the mystery of how DNA holds and transmits information.
At the heart of the DNA molecule are four basic chemical building blocks, called nucleotides. Each nucleotide has a sugar, a phosphate group, and a nitrogenous base. The nitrogenous bases are adenine (A), thymine (T), cytosine (C), and guanine (G). The sequence of these bases determines the genetic code, much like the letters of the alphabet form words and sentences.
The double helix structure of DNA, discovered by James Watson and Francis Crick in 1953, is a crucial factor in its ability to hold information. The two strands of the helix are held together by hydrogen bonds between the nitrogenous bases, with A always pairing with T and C always pairing with G. This base-pairing creates a complementary code: if you know one strand of DNA, you can deduce the sequence of the other.
But how is this information used by cells? DNA must be copied, or replicated, before cells divide. Enzymes unwind the double helix and use each strand as a template to build a new complementary strand. This results in two identical DNA molecules, each with one original and one new strand.
DNA is also used to make RNA, a molecule that carries the genetic code out of the nucleus and into the cytoplasm of the cell. RNA is made by copying a portion of the DNA code, with the letter T replaced by uracil (U). This process, called transcription, results in a single-stranded RNA molecule that can be read by ribosomes to build proteins, the workhorses of the cell.
DNA is not a perfect molecule, however. Mutations, or changes to the genetic code, can occur due to errors in replication or exposure to mutagenic agents like radiation or chemicals. Some mutations can be harmless, while others can cause diseases like cancer.
Despite its complexity, DNA is essential to life as we know it. By understanding how it holds and transmits information, we can better understand our own biology and unlock the secrets of diseases that plague us.
