Adenine, C5H5N5, is a purine, a ring-shaped organic compound. Just about every biology student will be familiar with adenine as the “A” in “A-G-C-T,” the four bases of DNA.
Adenine, of course, also appears in RNA. Adenine bonds by hydrogen bonds with thymine to stabilize DNA, and it forms hydrogen bonds with uracil to stabilize RNA. But adenine has many functions beyond its role in genetic material and protein transcription.
Derivatives of adenine play a variety of roles in the metabolism of the cell, including cellular respiration, forming the energy-rich adenosine triphosphate (ATP), as well as its cofactors flavin adenine dinucleotide (FAD), nicotinamide adenine dinucleotide (NAD), and Coenzyme A.
Adenine exists as several tautomers, considered to be biochemically equivalent. Isolated from the cell, adenine mostly exists as the 9H-adenine tautomer.
What do introductory biology students need to know about adenine?
- Along with guanine (“G”), adenine is one of the two purine bases that form nucleotides in the nucleic acids DNA and RNA. Adenine is hydrogen-bonded to the pyrimidine base thymine in the helix of DNA, stabilizing the structure. It is hydrogen-bonded with another pyrimidine base, uracil, to stabilize RNA.
- Adenine forms the nucleoside adenosine when it is chemically attached to ribose sugar. It forms the nucleoside deoxyadenosine when it is chemically attached to deoxyribose sugar. Adding three phosphate groups to adenosine creates adenosine triphosphate, better known as ATP. ATP is the cell’s main way of storing energy released by respiration and other chemical reactions.
Main Characteristics of Adenine
Adenine was once thought to be a vitamin. It was given the name vitamin B4. But when scientists confirmed that it can be synthesized by the body and does not have to be obtained from the diet, it was removed from the official vitamin B complex. However, two B vitamins, riboflavin and niacin (vitamin B2 and vitamin B3), combine with adenine to form the energy production cofactors FAD and NAD respectively.
German biochemist and Nobel laureate Albrecht Kossel discovered adenine in 1885. Because he discovered it in the pancreas, an exocrine gland, he named it after the Greek term for a gland, “aden.”
Spanish biochemist and exobiologist Joan Oró i Florensa conducted experiments in the 1950s and reported in 1961 that showed that ammonia and hydrogen cyanide molecules colliding in water can create adenine. His experiments showed that this important building block of all living things on Earth could have formed inside comets that are rich in carbon and water, affirming the idea that life on Earth could have extraterrestrial origins.
Fifty years later, a NASA report of an analysis of meteorites found on earth concluded that not just adenine but also guanine could have formed in outer space. NASA scientists found that adenine is unusually robust when exposed to ionizing radiation. Even if it is bombarded with radiation in outer space, it maintains its chemical integrity so that it can participate in the chemical reactions that are essential to life.
Adenine, as an isolated chemical, is a liquid. Its melting point is -129° C ( -265° F). Its molecular weight is 135.127. Compounds that contain adenine can be identified in the lab by a specialized technique known as capillary zone electrophoresis.
Modern Biology Students Experiments
Modern biology students can learn more about the role of adenine in DNA in Modern Biology’s Experiment B1: Structure, Isolation, and Function of DNA. Designed for 16 students working in pairs, this experiment gives students practical experience introducing them to the structure of DNA, the isolation of DNA, cell fractionation, and gene cloning procedures.
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