Nucleotide: Definition, Parts, Types and Functions

Fundamental organic compound of nucleic acids.

They are organic molecules that are the essential components of DNA and RNA. They also have functions related to cell signaling, metabolism, and enzymatic reactions.

The nucleotides are composed of three parts, a phosphate group, a sugar of 5 carbons, and a nitrogenous base. The four nitrogenous bases in DNA are adenine, cytosine, guanine, and thymine.

RNA contains uracil instead of thymine. Nucleotides form the DNA and RNA of all living beings.

Parts of the nucleotide

Each nucleotide is formed by a phosphate group, a sugar of 5 carbons, and a nitrogenous base. In DNA, 5-carbon sugar is deoxyribose, while in RNA, 5-carbon sugar is ribose.

This gives its names to DNA and RNA; the full name of DNA is deoxyribonucleic acid, and RNA is ribonucleic acid.

DNA and RNA contain all the genetic information necessary for cells to function. In DNA and RNA, many nucleotides join together to form long strands in a double helix structure.


The phosphate group and the five-carbon sugar make up the spine of the double helix, while the nitrogenous bases are in the middle and are linked together.

The phosphates and sugars form a backbone, and the nitrogenous bases join together in the middle of the double helix.

Types of nitrogenous bases in nucleotides

The five nitrogenous bases found in nucleotides are adenine, cytosine, guanine, thymine, and uracil. They are often abbreviated to A, C, G, T, and U.

  • Adenine: Adenine is a purine, one of two nitrogenous base families. The purines have a double ring structure. In DNA, adenine binds with thymine. In RNA, adenine binds with uracil.
  • Cytosine: The other family of nitrogenous bases is pyrimidine. Cytosine is a pyrimidine; it has only one ring in its structure and links with guanine in both DNA and RNA.
  • Guanine: Like adenine, guanine is a purine; It has a double circle. It binds with cytosine in DNA and RNA.
  • Thymine: Like cytosine, thymine is a pyrimidine and has a ring. It binds with adenine in DNA. Thymine is not found in RNA.
  • Uracil: It is also a pyrimidine. It binds with adenine in the RNA; It is not found in DNA.

More on nitrogenous bases

These paired nitrogenous bases form the middle of the double helix structure. A purine permanently binds with a pyrimidine, but more specifically, each floor binds with its complementary base: A with T (or U, in RNA), C with G, and vice versa.

When the nitrogenous bases of two nucleotides are joined, they are called base pairs. The grounds are connected through hydrogen bonds. Hydrogen bonds can be quickly released so that the DNA can be “decompressed” during the replication process.

Sometimes, the incorrect nitrogenous base is inserted into the DNA copy when the DNA replicates. There are mechanisms to correct these errors, but some go unnoticed because DNA does not have an adequate base pair.

These are called point mutations and can affect the functioning of a gene. Most point mutations are harmless, but they can be transmitted to the offspring if they occur in sperm or eggs.

Sickle-cell anemia is an example of a disorder caused by a single point mutation in the gene that creates hemoglobin, which is the part of the red blood cells that carries oxygen to the rest of the body.

Functions of nucleotides

In addition to being the basic unit of genetic material for all living beings, nucleotides also have other functions. These are found in other molecules, such as adenosine triphosphate (ATP), the cell’s primary energy molecule.

They are also found in coenzymes such as NAD and NADP, which come from ADP; These molecules are used in many chemical reactions that play a role in metabolism.

Another molecule that contains nucleotides is cyclic AMP (cAMP). This messenger molecule is essential in many processes, including regulating metabolism and the transport of chemical signals to cells.

Nucleotides are not only the essential components of life, but they also form many different molecules that work to make life possible.

Related biology terms

Deoxyribonucleic acid (DNA): A molecule that contains all the genetic instructions that allow an organism to function.

Ribonucleic acid (RNA): A DNA-like molecule that plays a role in many activities, such as protein synthesis, gene expression, and aiding chemical reactions.

Nitrogen base: A nitrogen-containing molecule that is one of the components of a nucleotide. The nitrogenous bases in DNA and RNA are adenine, cytosine, guanine, thymine and uracil.

Purine: One of the two families of molecules of nitrogenous base pairs. Purines have a double ring structure; the other family is pyrimidines, with only one ring.