Fatty acid synthesis involves the multistep synthesis of fatty acids for the purpose of energy storage in the organism. It represents only one part of fat metabolism, which in turn is integrated into overall metabolism. Under normal dietary conditions, fatty acid synthesis is of less importance to humans because the diet already contains fats.
What is fatty acid synthesis?
Fatty acids are stored in esterified form as fats or oils in specific cells designed for this purpose. Fatty acid synthesis is also known by the scientific name lipogenesis. It represents an anabolic, assimilative metabolic process that serves to store energy reserves for the organism. This applies to bacteria and fungi as well as to plants and animals. The basis of lipogenesis is the presence of several important starting compounds, vitamins and enzymes. A central position in the synthesis is occupied by malonyl-CoA, which is formed from acetyl-CoA by carboxylation (addition of carbon dioxide) under enzymatic conditions. Acetyl-CoA originates from various metabolic pathways. It occurs as an intermediate product during glycolysis (sugar metabolism), during fatty acid degradation or during protein metabolism. With the help of enzymes (acetyl-CoA carboxylase, fatty acid synthetase), energy transmitters (ATP, ADP), and vitamins (biotin, pantothenic acid), fatty acid synthesis is then controlled.
Function and task
For the survival of any organism, the storage of energy has a very great importance. Early in evolution, fatty acid synthesis emerged as an ideal way to store energy. Fatty acids are stored in esterified form as fats or oils in specific cells designed for this purpose. Other fatty acid esters also play a major role in building cell membranes. To produce energy stores, the fatty acids are esterified with the trivalent alcohol glycerol. In cell membranes, they are esterified with phosphorus-containing compounds. Furthermore, fatty acids form the basis for the synthesis of cholesterol and various hormones (sex hormones, glucocorticoids, mineralocorticoids). Chemically, they represent long-chain molecules with a carbon chain and a carboxyl group. Sometimes the chain is branched. Double bonds can also be present in the carbon chain from time to time. These are then unsaturated fatty acids. Saturated fatty acids contain only single bonds. These small differences in structure are responsible for the large number of possible functions of this group of substances. However, their main function is the storage of energy. The starting substances for fatty acid synthesis are produced via each metabolic pathway. Thus, carbohydrates, proteins and fats always produce acetyl-CoA as an intermediate product during their degradation. In the mitochondria, acetyl-CoA is degraded to carbon dioxide and water to produce energy. However, it can also be used in the cytoplasm to synthesize new fatty acids. For this purpose, it is first converted into malonyl-CoA and ADP with the aid of ATP under carboxylation and energy absorption. Malonyl-CoA in turn undergoes enzymatic condensation with acetyl-ACP. The resulting butyryl-ACP is again condensed with malonyl-CoA. These condensations are repeated until fatty acids with a chain length of up to 16 carbon atoms have been produced. Under normal conditions, fatty acid synthesis is of secondary importance in humans. This is due, among other things, to the fact that the diet usually contains a sufficiently large proportion of fat. Thus, the fats present in the diet are broken down into fatty acids and, if necessary, esterified back into fat. Furthermore, in a balanced diet, energy intake and energy demand are also balanced. In the past, however, periods of hunger often occurred, so that the body had to take in more energy in the form of food at times of excess supply in order to store fat reserves for times of need. The same is still true today for animals that have to hibernate to survive the winter. For them, fatty acid synthesis possesses great importance because they are additionally dependent on carbohydrate-rich food to create fat reserves.
Diseases and ailments
In the context of health problems, both excessive and insufficient fatty acid production play a major role. Today, diet-related diseases are becoming increasingly common.In times of food surplus, the number of overweight or even obese people is increasing more and more. As a result of a high-calorie and high-carbohydrate diet, fatty acid synthesis is boosted in the body. Normally, the biosynthesis of fatty acids should play only a minor role today. But due to the excessive supply of food, stress or psychological problems, people often eat too much. The resulting obesity poses major challenges for the health care system. Consequential diseases include diabetes mellitus, arteriosclerosis, cardiovascular diseases, dementia or other degenerative diseases. This trend can only be counteracted by a healthy lifestyle with a low-carbohydrate diet and physical exercise. In addition, energy intake and energy consumption should again be in balance. The hormone insulin controls the uptake of glucose into the cells for energy production. However, if less energy is consumed than is released, insulin is responsible for boosting fatty acid synthesis. In this case, the glucose is channeled into the fat cells, where the formation of new fatty acids immediately begins. The more the adipose tissue is filled with fat, the less effective insulin becomes. Via complicated metabolic processes, the number of insulin receptors on the cell membranes decreases. The result is a rise in blood glucose levels and an increase in insulin production until, if necessary, it stops completely. This also brings fatty acid synthesis to a standstill. For energy production, lipolysis in fat cells intensifies with increased ketone body formation, which causes the blood to become overacidified and may lead to diabetic coma.
