DNA Definition and Structure

What Is DNA?

DNA or deoxyribonucleic acid is a cell's code for making proteins.
DNA or deoxyribonucleic acid is a cell's code for making proteins. Scott Tysick, Getty Images

DNA Definition

DNA is the acronym for deoxyribonucleic acid, usually 2'-deoxy-5'-ribonucleic acid. DNA is a molecular code used within cells to form proteins. DNA is considered a genetic blueprint for an organism because every cell in the body that contains DNA has these instructions, which enable the organism to grow, repair itself, and reproduce.

DNA Structure

A single DNA molecule is shaped as a double helix made up of two strands of nucleotides that are bonded together.

Each nucleotide consists of a nitrogen base, a sugar (ribose), and a phosphate group. The same 4 nitrogen bases are used as the genetic code for every strand of DNA, no matter which organism it comes from. The bases and their symbols are adenine (A), thymine (T), guanine (G), and cytosine (C). The bases on each strand of DNA are complementary to each other. Adenine always binds to thymine; guanine always binds to cytosine. These bases meet each other in the core of the DNA helix. The backbone of each strand is made of the deoxyribose and phosphate group of each nucleotide. The number 5 carbon of the ribose is covalently bonded to the phosphate group of the nucleotide. The phosphate group of one nucleotide binds to the number 3 carbon of the ribose of the next nucleotide. Hydrogen bonds stabilize the helix shape.

The order of the nitrogenous bases has meaning, coding for amino acids that are joined together to make proteins.

DNA is used as a template to make RNA through a process called transcription. The RNA uses molecular machinery called ribosomes, which use the code to make the amino acids and join them to make polypeptides and proteins. The process of making proteins from the RNA template is called translation.

Discovery of DNA

The German biochemist Frederich Miescher first observed DNA in 1869, but he did not understand the function of the molecule.

In 1953, James Watson, Francis Crick, Maurice Wilkins, and Rosalind Franklin described the structure of DNA and proposed how the molecule could code for heredity. While Watson, Crick, and Wilkins  received the 1962 Nobel Prize in Physiology or Medicine ""for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material," Franklin's contribution was neglected by the Nobel Prize committee.

Importance of Knowing the Genetic Code

In the modern era, it's possible to sequence the entire genetic code for an organism. One consequence is that differences in DNA between healthy and sick individuals can help identify a genetic basis for some diseases. Genetic testing can help identify whether a person is at risk for these diseases, while gene therapy can correct certain problems in the genetic code. Comparing the genetic code of different species helps us understand the role of genes and allows us to trace the evolution and relationships between species.