Purine

The two main purines found in nucleic acids are adenine (A) and guanine (G).

Adenine

Adenine (A) is a purine nucleobase which plays a critical role in storing and transmitting genetic information. Within DNA, adenine pairs with thymine (T) via hydrogen bonds, forming the double helix structure. In RNA, uracil (U) replaces thymine and also binds with adenine.

To form nucleotides, adenine combines with a pentose sugar (ribose in RNA, deoxyribose in DNA) and a phosphate group. The resulting molecule is named based on the base and sugar type: “adenosine” for adenine and ribose, “deoxyadenosine” for adenine and deoxyribose. Nucleotides can have one, two, or three phosphate groups attached, denoted by suffixes like “monophosphate,” “diphosphate,” and “triphosphate” (e.g., adenosine triphosphate, ATP). Both DNA and RNA are polymers constructed from these nucleotides.

Hydrogen bonding between complementary bases (adenine with thymine in DNA, adenine with uracil in RNA) is crucial for maintaining the structure of nucleic acids and facilitating processes like DNA replication and protein synthesis. These hydrogen bonds can also participate in enzymatic reactions, influencing their rates.

Guanine

Guanine, denoted by the letter G, is a purine nucleobase with the chemical formula C5H5N5O. Found in both DNA and RNA, guanine forms hydrogen bonds with cytosine, a complementary pyrimidine nucleobase. Guanine, along with adenine and cytosine, is present in both DNA and RNA. However, thymine is typically found only in DNA, while uracil takes its place in RNA. Dietary sources of guanine are primarily animal-based, with high concentrations found in organ meats like liver, brain, and kidneys. Plant sources like peas, beans, and lentils contain smaller amounts.

Guanine exists in two tautomeric forms: the predominant keto form and the rare enol form. When paired with cytosine in DNA or RNA, three hydrogen bonds form between the two molecules. In cytosine, the amino group acts as the hydrogen bond donor, while the C-2 carbonyl group and the N-3 amine group in guanine act as hydrogen bond acceptors. The C-6 carbonyl group in guanine serves as an additional hydrogen bond acceptor, while the N-1 position and the amino group at C-2 in guanine act as hydrogen bond donors.

The nucleic acid is an important molecule in living organisms. Nucleic acid functions as the blueprint for genetic information. Understanding the nucleic acid structure and functions helps in deciphering the genetic code, which contains instructions for building and maintaining living organisms.

In this article, we will cover nucleic acid definition, structure, functions, formula and more.