Guide To Learn
Francis Jacob and Jacques Monod described the operon model in 1961, based on the regulation of lactose metabolism by the intestinal bacterium E. coli. Lactose operon is an ‘inducible operon’, because lactose induces the transcription of the operon. The lac operon is normally off, but when a molecule called an ‘inducer’ is present, the operon turns on. The lac operon […]
There are four different patterns of gene regulations namely negatively inducible, negatively repressible, positively inducible and positively repressible gene regulations (Figure 7.1). Figure 7.1 Types of gene regulation Table 7.1 Types of operon
Some substances called ‘inducers’ are capable of inducing or activating the expression of genes. In the presence of such inducers, the genes are transcribed and translated to synthesize the enzymes, which then metabolize the inducer. This phenomenon is called ‘induction’ and the enzymes synthesized are called ‘inducible enzymes’. For example, when E. coli is grown in the […]
Some gene products are required at all time and their genes are expressed at more or less constant level in all cells of a species or organism. The genes for the enzymes that catalyse the steps in a central metabolic pathway such as citric acid cycle fall in this category. These genes are called housekeeping […]
Prokaryotes live in a diversified environment ranging from the human intestine to polluted ponds, rivers, etc. and are thus exposed to different metabolites and molecules. Prokaryotes can survive in such a wide range of ecological conditions because of their ability to ‘switch on’ and ‘switch off’ the expression of specific sets of genes in response […]