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Intramyocellular lipids (or IMCL) are fats stored in droplets in muscle cells.They provide an important energy source for working muscle. During exercise, a large amount of circulating free fatty acids are directed into muscle cells for energy; during rest, incoming fatty acids are instead stored in the muscle cell as triglycerides for later burning. [1]
Animal cells maintain proper levels of intracellular lipids (fats and oils) under widely varying circumstances (lipid homeostasis). [ 8 ] [ 9 ] [ 10 ] For example, when cellular cholesterol levels fall below the level needed, the cell makes more of the enzymes necessary to make cholesterol.
This image illustrates the three separate steps of hydrolysis involved in lipolysis. In the first step, triacylglycerol is hydrolyzed to make diacylglycerol and this is catalyzed by adipose triglyceride lipase (ATGL). In the second step, diacylglycerol is hydrolyzed to make monoacylglycerol and this is catalyzed by hormone-sensitive lipase (HSL).
Lipid metabolism is the synthesis and degradation of lipids in cells, involving the breakdown and storage of fats for energy and the synthesis of structural and functional lipids, such as those involved in the construction of cell membranes.
The unusual microscopic anatomy of a muscle cell gave rise to its terminology. The cytoplasm in a muscle cell is termed the sarcoplasm; the smooth endoplasmic reticulum of a muscle cell is termed the sarcoplasmic reticulum; and the cell membrane in a muscle cell is termed the sarcolemma. [9] The sarcolemma receives and conducts stimuli.
Hydrolysis of sphingomyelin is catalyzed by the enzyme sphingomyelinase.Because sphingomyelin is one of the four common phospholipids found in the plasma membrane of cells, the implications of this method of generating ceramide is that the cellular membrane is the target of extracellular signals leading to programmed cell death.
Lipid droplets, also referred to as lipid bodies, oil bodies or adiposomes, [1] are lipid-rich cellular organelles that regulate the storage and hydrolysis of neutral lipids and are found largely in the adipose tissue. [2] They also serve as a reservoir for cholesterol and acyl-glycerols for membrane formation and maintenance.
Cholesterol is the principal sterol of all higher animals, distributed in body tissues, especially the brain and spinal cord, and in animal fats and oils. [3] [4]Cholesterol is biosynthesized by all animal cells [5] and is an essential structural and signaling component of animal cell membranes.