Nucleotide Structure

Nucleotides are molecules which, when joined together, help to make up and form the structural units of RNA and DNA. Furthermore, nucleotides also play a central role in metabolism. They also serve as a source of chemical energy. This is because adenosine triphosphate and guanosine triphosphate are also a part of the nucleotide structure. Nucleotides also participate in cellular signaling and are also important cofactors for enzymatic reactions, like coenzyme A, flavin mononucleotide, etc.

What is The Structure of a Nucleotide?

Base Molecule
Nucleotide bases are parts of the DNA and RNA that may be involved in pairing and are thus, an important part of the nucleotide structure. There are a total of five primary bases that are a part of either DNA or RNA. These are cytosine, guanine and adenine (all of which are common to DNA and RNA both), thymine (which is present only in DNA and not in RNA) and uracil (which is present exclusively in RNA only). These are abbreviated as C, G, A, T and U respectively. Uracil replaces thymine in RNA. The chemical structure of uracil is much simpler than that of thymine. These two bases are identical except for the fact that uracil lacks the 5' methyl group. Adenine and guanine belong to the double ringed class of molecules that are more commonly known as purines, whereas cytosine, thymine and uracil are a part of pyrimidines. Nucleotides can contain either a purine or pyrimidine base.

Phosphate Group
The phosphate group can be represented either as a sole phosphate ion or as a phosphoric acid molecule. This is an inorganic chemical that is found in the carbon rings and is an important part of the nucleotide structure. The phosphate groups form bonds with either the 2, 3, or 5-carbon of the sugar, with the 5-carbon site being the most common choice for attachment of the phosphate group. Cyclic nucleotides are those where the phosphate group is bound to two of the sugar's hydroxyl groups. It is due to the presence of the phosphate group that this molecule can become a hub of energy, as it is when phosphate bonds break that energy is produced. Nucleotides also exist in activated forms that contain two or three phosphates, and is called nucleotide diphosphates or triphosphates.

Sugar Group
The five carbon sugar that is present may either be a ribose sugar or a deoxyribose sugar. If the sugar present in the nucleotide structure is ribose, then it is known as a ribonucleotide, whereas if the sugar present is deoxyribose, then it is known as deoxyribonucleotide. Ribose is an organic compound which has five carbon atoms, ten hydrogen atoms and five oxygen atoms. This is specifically true for a monoosaccharide, which is a simple sugar. This term may refer to any of two enantiomers as well, almost always though to D-ribose, which occurs widely. This forms the backbone of RNA, which in turn, forms the basis of genetic transcription. It is though related to deoxyribose, which is found in DNA. Ribose is an aldopentose as it contains five carbon atoms and forms an open chain.

Nucleic acids are polymeric macromolecules that are made from nucleotide monomers. DNA and RNA are synthesized in cells by DNA polymerases and RNA polymerases. Short fragments of nucleic acids also are commonly produced without enzymes by oligonucleotide synthesizers. The basic structure though of nucleotide is important to understand. This is because nucleotide structure is a basic unit and is often said to be the common length unit for single-stranded RNA, similar to how base pair is considered to be a length unit for double-stranded DNA.