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  Section: Genetics » Mutations » Biochemical Level (Biochemical and Microbial Genetics)
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Mutations : 2. Biochemical Level (Biochemical and Microbial Genetics)

Mutations : 2.  Biochemical Level (Biochemical and Microbial Genetics)
Inborn errors of metabolism in man
Eye transplantation in Drosophila
Biochemical mutations in Neurospora
Mutations in E. coli for resistance against phages or antibiotics
Cell counting in suspension
Calculation of mutation rates and frequencies
Biochemical mutations and biosynthetic pathways
Gene sequences and enzyme sequences in biosynthetic pathways
Genes control various traits in an organism through a control exercised on the developmental processes. Such a control is due to synthesis of proteins, which is under direct control of genes. Some of these proteins synthesized by genes are enzymes and control biosynthetic pathways. That genes express themselves through synthesis of enzymes was demonstrated for the first time in 1941 by G.W. Beadle and E.L. Tatum (both Noble Prize winners of 1958), due to their discovery of biochemical mutations in Neurospora. Based on their work, Beadle and Tatum proposed a concept called one gene-one enzyme hypothesis. Such a hypothesis means that if in a biosynthetic pathway several steps are involved, each step is controlled by a specific enzyme, which is synthesized under the control of a specific gene (Fig. 22.1). Mutations in these genes helped in elucidating several biosynthetic pathways in a variety of organisms, particularly in microbes like fungi and bacteria. This will be illustrated with the help of some examples in this section. For the study of these biochemical mutations and mutations for resistance against phages and antibiotics, microbial systems have proved to be particularly useful.

Large populations can be handled in these microbes, so that even rare recombinants and mutations, with very low frequencies, can be easily detected. This has given rise to an area of study in genetics, popularly described as 'microbial genetics', which may also include biochemical genetics. Cases of mutations for resistance against phages and antibiotics in bacteria will also be described briefly in this section (for more details on bacterial genetics, consult Sexuality and Recombination in Bacteria and Viruses).
Diagrammatic representation of the biosynthesis of a product C involving three steps.
Fig. 22.1. Diagrammatic representation of the biosynthesis of a product C involving three steps.


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