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DNA Structure: Nucleotide versus Nucleoside

written by: •edited by: Paul Arnold•updated: 10/3/2011

They're almost spelt the same, nearly sound the same and are key components of the DNA structure. Both are needed to create and replenish cells, but don't be confused by the terms nucleotide and nucleoside. This article is a brief look at their key differences.

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    Nucleotides in a DNA Structure

    A nucleotide is composed of a nitrogenous base (i.e. adenine, guanine, cytosine, thymine) a five-carbon sugar, and three phosphate groups.

    Nucleotides are key structural components of two crucial nucleic acids DNA and RNA; they are its building blocks. When DNA is being expressed, the nucleotides make up a chain (or sequence) that codes for amino acids that eventually becomes a part of a protein. Therefore, nucleotides allow for the development of several processes of a living organism to occur based on a genetic code.

    Nucleotides have a double-bonded oxygen at the first carbon that can bond with a nitrogenous base. The third carbon of the base is what bonds with the nucleotide. The hydroxyl (OH) at carbon two is what makes the difference between a ribose (in RNA) and a deoxyribose (in DNA). The fifth carbon bonds with the phosphate.

    Nucleotides are also important for metabolism as well as the maintenance and enhancement of cellular immunity.

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    Nucleosides

    Nucleosides consist of a nitrogenous base bound to a ribose or deoxyribose sugar and are made by the hydrolysis of a nucleic acid. Nucleosides can be made in the liver from consumed food that contains nucleic acids. These nucleic acids break down the nucleotides into nucleosides. The breakdown of nucleotides into nucleosides also occurs in the lumen of the digestive system and inside cells.

    Nucleosides can also be used as antiviral and anticancer agents. Specifically, analogs of them are used in antiviral and antitumor therapy.

    A diet rich in nucleosides is important for optimal health.

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    Quick Summary

    Here is a quick and handy summary of the key difference between nucleotides and nucleosides.

    A nucleotide has a nitrogenous base, a sugar and a phosphate group.

    A nucleoside has a nitrogenous base attached to a ribose or deoxyribose sugar and is without a phosphate group.