Cellular metabolism is the general term for the ordered series of chemical reactions that occur within cells to sustain life. These reactive processes allow organisms to grow and reproduce, maintain their structure, and respond to the external environment.
Metabolism is usually divided into two categories: catabolism, which breaks down large molecules for energy (e.g., cellular respiration), and anabolism, which uses energy to synthesize components of the cell, such as glycogen, proteins, and nucleic acids. Metabolism plays a key role in the fields of physiology, cell biology and medicine.
Disturbances in metabolic pathways can lead to many common human diseases such as cancer, diabetes, obesity, hypoglycemia, hypolipidemia, phenylketonuria, neurodegeneration, etc.
Glycolysis
Glycolysis is the 10-step process by which glucose is broken down into pyruvate and ATP within the cell, using a series of enzymes to convert each six-carbon glucose molecule into two three-carbon pyruvate molecules. The pathway is common to virtually all cells in both prokaryotes and eukaryotes. In eukaryotic cells, glycolysis occurs in the cytoplasm. The pathway consists of three stages: 1) conversion of glucose to fructose 1,6-diphosphate; 2) cleavage of fructose 1,6-diphosphate into two three-carbon fragments; and 3) oxidation of the three-carbon fragments to pyruvate (to obtain ATP and NADH). The key regulatory enzyme is phosphofructokinase, and step 3 of glycolysis is an irreversible reaction and is the rate-limiting step of the process.
Lipid metabolism
Lipid metabolism is an important and complex biochemical reaction in the body, referring to the process of digestion, absorption, synthesis and breakdown of fats in living organisms with the help of various related enzymes. Lipids are important substances for energy storage and supply in the body, and they are also important structural components of biological membranes. The digestion of fats in animals is mainly in the upper part of the small intestine by the action of various enzymes and bile salts, which are hydrolyzed into glycerol, fatty acids, etc.
Lipids are absorbed in two ways: triglycerides composed of medium- and short-chain fatty acids are absorbed after emulsification and enter the blood through the portal vein; triglycerides composed of long-chain fatty acids combine with apolipoproteins and cholesterol to form celiac particles and finally enter the blood through the lymph.
Triglycerides are an important form of energy storage and oxidative energy supply for the body. The glycerol and fatty acids required for triglyceride synthesis are mainly provided by glucose metabolism. Different tissues synthesize triglycerides in different ways. Synthesis pathway in hepatocytes and adipocytes: the diglyceride pathway. Synthesis pathway in small intestinal mucosal cells: monoglyceride pathway. Catabolism of triglycerides is the process of fat mobilization, where fat stored in adipocytes is progressively hydrolyzed by lipase into free lipoic acid (FFA) and glycerol and released into the bloodstream to be oxidized and utilized by other tissues.
Coenzymes and Cofactors
Coenzymes are organic molecules that bind to enzymes to help catalyze reactions. They usually bind to the active site of the enzyme and contribute to substrate recruitment. Coenzymes, like enzymes, can be recycled repeatedly without changing the rate or effect of the reaction. Most are in the form of vitamins, vitamin derivatives or nucleotides.
Cofactors are “helper molecules” and can be inorganic or organic in nature. They usually include metal ions, such as iron, zinc, cobalt and copper. Since most organisms are unable to synthesize metal ions, they must be supplemented in the diet. Coenzymes and cofactors play an integral role in many cellular metabolic reactions and play a catalytic role in both structure and function.
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