What Is a Kilobase?

Jillian O Keeffe

A kilobase is a numbering measurement used in the field of genetics. As a base is one building block of genetic information, and every organism contains many bases, 1,000 bases is a common number to use when discussing how many bases an organism's genetic library contains. This 1,000 base chunk is more properly referred to as a kilobase.

Scientist with beakers
Scientist with beakers

Every living organism contains genetic information. This information spells out to the organism exactly which protein products the organism needs to live, grow, and multiply. All of the genetic information together is called the genome of the organism.

Each genome is split into discrete sections. These sections, called genes, code for a particular product. Each gene contains a string of building blocks, called bases. When the organism reads the genes to produce a particular product, it is the sequence of bases inside the gene that it reads.

Only four bases exist in the genetic material DNA. These are cytosine (C), guanine (G), thymine (T), and adenine (A). It is the order in which the bases are arranged in a gene that dictates what that gene codes for. The complexity necessary to produce all the products essential for human life arises from the length of the genes and the number of the bases inside them.

Genes each contain a remarkable number of bases. The entire human genome, for example, contains 3 billion bases, each paired with another base in a spiral helix structure. The sheer amount of bases present in a genome mean that geneticists find it easier to refer to genes as being x kilobases in length, as opposed to 1,000 times x in length.

Even the smallest of genomes, such as the Carsonella ruddii bacterium genome, hold about 160,000 base pairs. This tiny genome is about 160 kilobases (kb) in length. The human genome, on the other hand, is 3 million kilobase pairs in length.

Sequencing of genomes requires that the genome be broken up first. Equipment that performs the sequencing can only handle so many bases at one time. Geneticists can split up a genome into many sections and refer to them as containing so many kilobase pairs, such as a length of 150 kilobase pairs. This size of genetic material can be genetically engineered into another organism in order to multiply the DNA up to a level that is easily readable. Even these relatively small pieces of DNA are too long for sequencing directly, so geneticists may then break up a 150-kb segment into much smaller portions of a few hundred bases in length.

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