Mutants are the organisms in which a given enzyme fails to be synthesized in its active form due to a genetic disorder. Study of mutant organism which failed to synthesize certain proteins is one of the important ways of studying the metabolism. Such type of defect often results in the accumulation and excretion of the substrate of the defective enzyme. This enables us to understand steps in the metabolic pathways. Since such genetic disorders are rare, systematic study of metabolic pathways is difficult. Genetic defects can be produced at will in micro-organisms by subjecting them to mutagenic agents, such as irradiation with x-rays or treatment with certain chemicals.
These treatments can alter the structure of specific genes in the DNA and thus produce mutants. Such mutants micro-organisms with their defective enzymes are powerful tools for studying metabolism. The cells of Neurospora crassa (a common mould) which can grow on a simple medium containing glucose and ammonia, can be study by the use of mutants. If Neurospora spars are irradiated with x-rays, the mutants obtained are no longer capable of going on a medium containing just glucose and ammonia. This type of mutants will grow only if specific metabolities are added to the medium. For example, some new tenants the whole not known if are denying is added to the medium.
This is because of absence of defectiveness of enzyme which responsible for the synthesis of argenine from ammonia, in such mutant. This type of argenine less mutant can be used to identify intermediates in the sequence of enzyme catalyzed reaction leading to the synthesis of argenine.