What is a Nucleotide?

Both DNA and RNA are composed of organic molecules known as nucleotides. Hence, nucleotides are known as the basic building blocks of nucleic acids. These substances play a role in various processes such as cell signalling, enzyme reactions, metabolism, and so on.

Nucleotides

Before knowing about the nucleotide one has two know what are DNA and RNA. DNA and RNA are the two nucleic acids found in a living organism. DNA is the chemical material that stores all the genetic information about the organism and RNA is the chemical substance that is involved in the synthesis of proteins in an organism.

The genetic material of all known living things is made up of nucleotides that make up a chain. As messengers and energy-moving molecules, they serve a variety of functions in addition to storing genetic information. Before knowing about the nucleotide one has two know what are DNA and RNA. DNA and RNA are the two nucleic acids found in a living organism. DNA is the chemical material that stores all the genetic information about the organism and RNA is the chemical substance that is involved in the synthesis of proteins in an organism.

Composition of a Nucleotide

A phosphate group, a 5-carbon sugar, and a nitrogenous base are the three components of a nucleotide. In a nucleotide a sugar molecule is attached to the phosphate group and nitrogenous base.

Nitrogenous Bases

These are the derivatives of the purines and pyrimidines. The nitrogenous bases adenine (A) and Guanine (G) are purine derived bases. While the bases Thymine (T), uracil (U), and cytosine (C) are pyrimidines.

Thymine is a nitrogenous base that is found only in DNA, in RNA is replaced by uracil.

Purine bases

The structures of these bases is a fused ring structure that contains a single amino group. They include the adenine and guanine.

Pyrimidine bases

These bases consist of a keto group that may or not be linked to an amino group or any other keto group in these nitrogenous bases. Unlike the purines, they have got a ring-like structure that is glued together.

Pentose sugars

These sugars are monosaccharides which have 5 carbon atoms. The pentose sugar found in the DNA is deoxyribose and the pentose sugar found in the RNA is ribose. The structures of both these sugars are different.

In deoxyribose, the OH group attached to the C-2' in ribose is substituted by hydrogen. As a result, deoxyribose is the sugar base unit in DNA.

A nucleotide may contain any one of these sugars.

Phosphate Group

These substances are the chemical derivatives of phosphoric acid. A single nucleotide comprises one or two or three phosphate groups. The nucleotides are made up of sugar, base, and one or two phosphate groups. The ones which have a single phosphate are known as monophosphates are the one which has two phosphate groups are known as diphosphates.

As mentioned above nucleotides also have three phosphates, are known as triphosphates. Such phosphates bond together and make up the nucleic acids DNA and RNA.

The phosphate group that is attached to the sugar and base unit is the final part of the nucleotide.

Naming Nucleotides

The nucleotides are named or coded by the type of sugar molecule, the number of phosphate groups and the type of nitrogenous base.

For example, dCTP refers to deoxy cytosine triphosphate while GMP refers to guanosine monophosphate. In the term dCTP “d” refers to deoxyribose sugar.

The Structure and Formation of Nucleotides

In this process, the nitrogenous base first attaches with the sugar molecule. This structure is known as the Nuceloside. The bond by which the nitrogenous base attaches to the sugar molecule

is known as the N- glycosidic bond. This bond connects the nitrogenous bases to the 1’ of the sugar base unit. Purines and pyrimidines are linked by N-9, while purines and pyrimidines are linked by N-1.

To this structure, the phosphate group attaches to the sugar molecule and forms the nucleotide.

Any two nucleotides are connected to each other by means of a phosphodiester bond. This bond connects the nucleotides by attaching to the 3’- OH free hydroxyl group of one sugar molecule to the 5’ OH- free hydroxyl group of other sugar molecule leading to the formation of long unbranched DNA and RNA chains. Starting from the 5' end, the

sequence of nucleotides in a nucleic acid is identified. DNA has a double-helical structure, while RNA has a single helical structure.

In the nucleic acid DNA which us a double helix the bases always occur in pairs. Three nucleotides together are known as a codon. The bases in the nucleotides are held together by the hydrogen bonds. The bases adenosine (A) and thymine (T) are combined, while cytosine (C) is paired with guanine (G) (G). Since they bind the two strands of DNA, they are called base complements. The complementary bases are found in the sugar backbone as rungs on a ladder.

Two hydrogen bonds connect adenine and thymine, while three hydrogen bonds connect guanine and cytosine. As a result, GC hydrogen bonding is much more efficient than AT hydrogen bonding. Hydrogen bonds hold the two helixes of DNA together. The sugar base units that make up DNA's skeleton are linked together by phosphodiester bonds. Another helix runs from 3' to 5' and another from 5' to 3'.

Function of Nucleotides

Nucleotides are the fundamental building blocks of nucleic acids (RNA and DNA). DNA is in charge of transmitting genetic information from one generation to the next, while RNA aids protein synthesis.

In the body, cyclic nucleotides such as cyclic AMP (Adenine monophosphate) and cyclic GMP (Guanine monophosphate) serve as regulatory chemicals. The role of calmodulin-mediated responses is aided by cGMP. In addition, cGMP stimulates a number of enzymes in the body. Below is an example of hormone activation, in which cAMP stimulates Protein Kinase and the hormone hits the target site. Coenzymes are made up of nucleotides and other molecules. Coenzymes are nutrients that help enzymes work more efficiently. B-complex vitamin nucleotides, such as NADP+, NAD+, and FMN, are coenzymes that support the body's oxidation-reduction reactions.

Nucleotides with a higher number of phosphate bonds, such as ATP, UTP, GTP, or TTP, serve as energy carriers. ATP is also known as the cell's energy currency. The explanation for this is that these molecules' phosphate bonds store a lot of energy. Energy is released when these bonds are broken, and is used in different cellular processes.

Context and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for,

• B.Sc. in Chemistry, Biotechnology, Biochemistry and Biology
• M.Sc. in Chemistry, Biotechnology, Biochemistry and Biology