Metabolic engineering is defined as the application of recombinant DNA technology to increase biological activity by manipulating the cell's enzymatic, transport, and regulatory processes. The purposeful manipulation of cellular metabolism for the generation of desired substances is known as metabolic engineering. The metabolic pathways of numerous species can be modified using recombinant DNA technology. Bacteria, fungi, plants, and mammal cells are all employed as host organisms, and the features of interested pathways are used to guide selection. The generation of PHAs in diverse microbes has advanced significantly owing to metabolic engineering. In addition to metabolic engineering, systems biotechnology has enabled the collection and analysis of extensive data from biological systems, providing for a degree of insight previously unreachable for the development of computer models. The ultimate goal of metabolic engineering is to be able to harness these organisms to create valuable compounds in a cost-effective manner on an industrial scale. Beer, wine, cheese, pharmaceuticals, and other biotechnology products are current examples. (1) overexpressing the gene encoding the biosynthetic pathway's rate-limiting enzyme, (2) inhibiting competing metabolic pathways, (3) heterologous gene expression, and (4) enzyme engineering is some of the main metabolic engineering procedures.