Genes introduction
The human genome is composed of three billion base pairs of DNA. These three billion base pairs are divided up among the 46 chromosomes that are present in every human cell. We inherit 22 autosomal (non-sex) chromosomes and one sex chromosome (X or Y) from each parent. These chromosomes vary in length from 50 million to 250 million base pairs. These 46 chromosomes are found in the nucleus of every one of the bodies trillions of cells. Each chromosome contains many genes, the basic physical and functional units of heredity.
Each gene contains the instructions of how to make a protein or proteins. The exact protein that is made is determined by the order of the DNA bases within the gene. It is believed that there are between 30,000 - 40,000 genes within the human genome. This is far fewer than the number that was predicted originally and only about twice the amount of genes that are present in the fly. Less than 2% of the human genome contains genes (coding regions). The rest of the genome is believed to be involved in providing chromosomal structural support and in regulating the amount of proteins produced in the different cells of the body and at different times. Although each cell in the body contains a full complement of the bodies 3 billion base pairs of DNA, they use the genes selectively.
The genes that make proteins that are needed for basic functions (called housekeeping genes) are active in most cell types. Genes that code for proteins that have more specific functions are only activated in cell types where that protein is needed. It is by expressing different genes and hence producing different combinations of proteins that the different cell types can fulfill their various roles eg. the genes expressed in a brain cell differs from a skin cell which differs from a liver cell. So at any one time a normal cell will activate only those genes that code for the proteins it needs and it will actively suppress all the other genes. Proteins are in fact what perform all of life's essential functions.
Changes in the DNA sequence of our genome - both coding and non coding - can have disasterous consequences. These changes can lead to the production of faulty malformed proteins that are incapable of performing their correct function or over or under production of a protein resulting in the complete disruption of certain cellular processes. These disruptions to protein structure and regulation are what cause many of the common diseases that we observe today (cancers, heart disease, diabetes).For these reasons scientists are excited that for the first time ever they can begin to explore the DNA sequence of our genome, search for the genes and attempt to pinpoint the DNA mutations that lead to common disease states.
