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The metabolic process of catabolism is the breakdown of big molecules. Food molecules are broken down and oxidised as part of this process. Catabolic reactions are designed to give the energy and components that anabolic reactions require. The specific nature of these catabolic events varies per organism; organisms can be classed based on their basic nutritional groups, which are their sources of energy and carbon. Organotrophs employ organic molecules as a source of energy, lithotrophs use inorganic substrates, and phototrophs use sunlight as a chemical energy source.

Redox processes involve the transfer of electrons from reduced donor molecules like organic molecules, water, ammonia, hydrogen sulphide, or ferrous ions to acceptor molecules like oxygen, nitrate, or sulphate in all of these distinct forms of metabolism. Complex organic molecules in animals are broken down into simpler ones like carbon dioxide and water in these reactions. These electron-transfer reactions are used to store energy acquired from sunlight in photosynthetic organisms such as plants and cyanobacteria, rather than releasing it.

Animal catabolic reactions can be divided into three stages. Large organic molecules including proteins, polysaccharides, and lipids are digested into smaller components outside of cells in the first stage. Cells then take these smaller molecules and convert them to even smaller molecules, most often acetyl coenzyme A (acetyl-CoA), which releases energy. Finally, in the citric acid cycle and electron transport chain, the acetyl group on CoA is oxidised to water and carbon dioxide, releasing the stored energy by decreasing the coenzyme nicotinamide adenine dinucleotide (NAD+) to NADH.

Starch, cellulose, and proteins are macromolecules that cannot be quickly absorbed by cells and must be broken down into smaller units before being employed in cell metabolism. These polymers are digested by a variety of enzymes. Proteases, which break down proteins into amino acids, and glycoside hydrolases, which break down polysaccharides into monosaccharides, are examples of digestive enzymes. Digestive enzymes are secreted into the environment by microbes, but they are exclusively secreted by specific cells in mammals' stomachs. Extracellular enzymes produce amino acids or carbohydrates, which are then pushed into cells by active transport proteins [1].

Carbohydrate Catabolism

The breakdown of carbohydrates into smaller components is known as carbohydrate catabolism. After being digested into monosaccharides, carbohydrates are normally absorbed into cells. Glycolysis, where carbohydrates like glucose and fructose are transformed to pyruvate and some ATP is created, is the main route of breakdown once inside. Pyruvate is a metabolic intermediate that is converted to acetyl- CoA and supplied into the citric acid cycle in the majority of cases. Although the citric acid cycle generates some additional ATP, the most critical result is NADH, which is produced from NAD+ as acetyl-CoA is oxidised. As a waste product of this oxidation, carbon dioxide is released. Glycolysis creates lactate in anaerobic settings, with lactate dehydrogenase reoxidizing NADH to NAD+ for re-use [2 - 5].

The pentose phosphate pathway, which decreases the coenzyme NADPH and produces pentose sugars like ribose, the sugar component of nucleic acids, is an alternate route for glucose breakdown. Hydrolysis breaks down fats into free fatty acids and glycerol. The fatty acids are broken down by beta oxidation to liberate acetyl-CoA, which is subsequently supplied into the citric acid cycle after the glycerol commences glycolysis. Because carbohydrates include more oxygen in their structures, fatty acids release more energy when they are oxidised.

Amino acids can be utilised to make proteins and other macromolecules, or they can be oxidised to produce urea and carbon dioxide as a source of energy. Several of these keto acids are intermediates in the citric acid cycle, such as -ketoglutarate, which is formed by the deamination of glutamate. Gluconeogenesis is a process that converts glucogenic amino acids into glucose [6].

s-thiazines are anthropogenic chemicals that are now known to be readily recycled by many soil bacteria. The genes and enzymes underlying this metabolism have been elucidated. There is evidence that s-thiazine metabolism has recently evolved, and the initiating reactions are almost invariably plasmid encoded. Arthrobacter species are being increasingly isolated and are particularly efficient at metabolizing s-thiazine compounds. This efficiency stems from the broad-spectrum TrzN enzyme initiating metabolism and from the ability to rapidly assimilate the alkyl amine fragments generated by AtzB and AtzC. The recent genome sequences of Arthrobacter strains help to reveal the core metabolism that underlies efficient s-thiazine metabolism. The nitrogen-metabolic genes on the Arthrobacter chromosome also reveal why this genus of bacteria has consistently been isolated for the catabolism of a wide range of organ nitrogen chemicals found in the environment [7-10].

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