|  | Public Health Safety | Medical Research

What Composes a DNA Nucleotide?

The nucleic acids found within the body are made up of smaller units called nucleotides. Those nucleotides form the genetic code of DNA, though they are essential components of all nucleic acids. Although nucleotides vary greatly in their exact makeup, they are always composed of a pentose sugar, a nucleobase and a phosphate group.

  1. The Pentose Sugar

    • Two varieties of pentose sugars, so called because of their five carbons, can be found in nucleotides. The two sugars are ribose and deoxyribose. Deoxyribose has one fewer oxygen atom than ribose. Ribose can be found in the nucleotides that form RNA, while deoxyribose is found in the nucleotides that build DNA.

    The Heterocyclic Nucleobase

    • The nucleobases adenine (A), guanine (G), cytosine (C), and thymine (T) make important contributions to the genetic code of DNA..

      The nucleobase attaches to the pentose sugar, forming a nucleoside. Bases always contain nitrogen and are classified as purines or pyramidines. The purines, found in both DNA and RNA, are adenine, "A," and guanine, "G." The pyramidines are cytosine, or "C"; thymine, or "T"; and uracil, "U." Uracil is exclusive to RNA and thymine is exclusive to DNA.

    The Phosphate Groups

    • Also parts of the nucleotide are one, two, or three phosphate groups. The phosphate groups, like the bases, are attached to the pentose sugar. According to Dr. John Kimball, DNA and RNA are built by nucleotides containing three phosphates. Also known as nucleoside triphosphates, those nucleotides drop two phosphate groups in the process of forming RNA or DNA.

    How Nucleotides Build DNA

    • DNA is normally arranged in a double helix -- two backbones joined by a ladder. The backbones are formed by the joining of nucleotide phosphates and sugars. The nucleobases are left free to pair together to form a ladder. In DNA, the only bases are adenine, guanine, thymine, and cytosine. Adenine can only pair with thymine and guanine can only pair with cytosine. The sequence of nucleobase pairs is an important part of the genetic code.

Medical Research - Related Articles