what is gene

agldacheng

The hereditary nature of every living organism is defined by its genome, which consists of a long sequence of nucleic acid that provides the information needed to construct the organism. We use the term \"information\" because the genome does not itself perform any active role in building the organism; rather it is the sequence of the individual subunits (bases) of the nucleic acid that determines hereditary features. By a complex series of interactions, this sequence is used to produce all the proteins of the organism in the appropriate time and place. The proteins either form part of the structure of the organism, or have the capacity to build the structures or to perform the metabolic reactions necessary for life.
The genome contains the complete set of hereditary information for any organism. Physically the genome may be divided into a number of different nucleic acid molecules. Functionally it may be divided into genes. Each gene is a sequence within the nucleic acid that represents a single protein. Each of the discrete nucleic acid molecules comprising the genome may contain a large number of genes. Genomes for living organisms may contain as few as <500 genes (for a mycoplasma, a type of bacterium) to as many as >40,000 for Man.
In this chapter, we analyze the properties of the gene in terms of its basic molecular construction. Figure 1.1 summarizes the stages in the transition from the historical concept of the gene to the modern definition of the genome.