What's a genome? Why is it important?
DOE Microbial Genome Program Report
All living things, including microbes, have a chemical called DNA (for deoxyribonucleic acid) that contains information used by the organism to build, maintain, and reproduce itself. DNA is made up of four chemical building blocks (bases) that are abbreviated A, T, C, and G. Thousands to millions of these bases, depending on the organism, form long strands that pair together (A with T and C with G) in a twisted zipper-like structure often described as a double helix.
All the DNA in an organism is called its genome. Genomes range widely in size: the smallest known bacterial genome contains about 600,000 base pairs and the human genome some 3 billion. Except for the order and number of bases in the genome, DNA from all organisms is made of the same chemical and physical components.
Genes are segments of DNA that contain instructions on how to make the proteins that comprise all the organism’s structures and run its functions. The genome of the microbe Mycoplasma genitalium, considered the smallest living organism, contains about 500 genes; in contrast, the human genome is estimated to contain some 140,000 genes [2003: now thought to contain about 35,000 genes]. Combinations of genes, often interacting with environmental factors, ultimately determine all the physical characteristics of an organism.
The sequence of DNA bases for a particular gene (e.g., ATCCTGC or CCATTCG) acts as a code that an organism’s cellular machinery understands and can translate into a specific protein. The ultimate goal of most genome projects is to determine the animal’s, plant’s, or microbe’s unique DNA sequence and identify the genes contained in that sequence. The genomes of many organisms, including humans, have much nongene (noncoding) DNA.
An increasing number of complete genome sequences are being generated and deposited into large and small public databases. The next great challenge—to understand the genome data—is the focus of a new and growing field called functional genomics, which will require the expertise of computer scientists and other investigators across a broad range of disciplines. Questions they might ask include, What are the functions of each gene? and How does it interact with all the other genes and environmental factors to create and maintain an organism?
The focus of DOE’s MGP is to use high-throughput, cost-effective DNA sequencing capabilities to provide information on microorganisms with potential environmental, energy, or commercial applications.
|The online presentation of this 2000 publication is a special feature of the Human Genome Project Information Web site.|