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Notes on Biochemical Genetics: 1. Gene Action 2. Metabolic Pathway 3. Metabolic Disorders 4. Genetic Control 5. Organisms Studied.
Biochemical Genetic: Point # 1. Gene Action:
The manner in which genes control phenotypic expression of various characters in an organism is known as gene action. In other words, gene action refers to the functioning of genes (hereditary units) in determining the structural and functional characteristics or phenotype of an individual.
Gene action is investigated through the study of biochemical nature of genes and their mode of action in biochemical pathway.
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Gene action is studied in two ways, viz:
(i) By the analysis of changes which occur in the phenotype when a gene mutates, and
(ii) By determining the direct effect of genes over metabolism in multicellular, differentiated organisms. Thus gene action is the expression of genes by their control on the specificity and rate of biosynthetic processes or on the regulated action of other genes.
Biochemical Genetic: Point # 2. Metabolic Pathway:
A definite sequential path of biochemical reactions is referred to as metabolic path way or biochemical pathway. In biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell. In each pathway, a principal chemical is modified by chemical reactions.
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These reactions are accelerated or more accurately catalyzed by enzymes. Thus metabolic pathway refers to a series of chemical reactions catalyzed by enzymes in a living system. The products of the pathways have vital functions.
Biochemical Genetic: Point # 3. Metabolic Disorders:
A genetically determined biochemical disorder that results in an enzyme defect is called metabolic disorder. Any of a group of congenital disorders caused by an inherited defect in a single specific enzyme that results in a disruption or abnormality in a specific metabolic pathway is known as inborn error of metabolism. The term inborn error of metabolism was coined by Archibald Garrod in 1908.
Inborn errors of metabolism comprise a large class of genetic diseases involving disorders of metabolism. The majority are due to defects of single genes that code for enzymes that facilitate conversion of various substances (substrates) into others (products).
In most of the disorders, problems arise due to accumulation of substances which are toxic or interfere with normal function, or reduce ability to synthesize essential compounds. Inborn errors of metabolism are now often referred to as congenital metabolic diseases or inherited metabolic diseases, and these terms are considered synonymous.
Biochemical Genetic: Point # 4. Genetic Control:
Genes control synthesis of proteins which in turn control expression of various traits of an organism. Garrod in 1909 postulated that inborn errors of metabolism are due to enzyme defects and enzyme defects are heritable. Thus, metabolic disorders or defects are genetically controlled. Such defects are caused by recessive mutations.
Biochemical Genetic: Point # 5. Organisms Studied:
Gene action was first studied by Sir Archibald Edward Garrod in man and subsequently by others in smaller organisms like Drosophila, Neurospora and bacteria.
