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Lipids are a broad group of organic compounds which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides, phospholipids, and others. The functions of lipids include storing energy, signaling, and acting as structural components of cell membranes.
Long-chain free fatty acids enter metabolizing cells (i.e. most living cells in the body except red blood cells and neurons in the central nervous system) through specific transport proteins, such as the SLC27 family fatty acid transport protein. [5] [6] Red blood cells do not contain mitochondria and are therefore incapable of metabolizing ...
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. In animals, these fats are obtained from food and are synthesized by the liver. [1]
Water and fiber are macronutrients, but do not provide energy. The micronutrients are minerals and vitamins. [7] The macronutrients (excluding fiber and water) provide structural material (amino acids from which proteins are built, and lipids from which cell membranes and some signaling molecules are built), and energy.
Many cell types can use either glucose or fatty acids as a source of energy for metabolism. In particular, heart and skeletal muscle prefer fatty acids. [ 246 ] [ 247 ] Despite long-standing assertions to the contrary, fatty acids can also be used as a source of fuel for brain cells through mitochondrial oxidation.
The formation of lipid droplets from the endoplasmic reticulum begins with the synthesis of the neutral lipids to be transported. The manufacture of TAGs from diacylglycerol (by the addition of a fatty acyl chain) is catalyzed by the DGAT proteins, though the extent to which these and other proteins are required depends on cell type. [34]
Proteins are essential nutrients for the human body. [1] They are one of the building blocks of body tissue and can also serve as a fuel source. As a fuel, proteins provide as much energy density as carbohydrates: 17 kJ (4 kcal) per gram; in contrast, lipids provide 37 kJ (9 kcal) per gram.
Carbohydrates contain 4 calories per gram. Lipids provide animals with fats and oils. They are not soluble in water, and they can store energy for an extended period of time. They can be obtained from many different plant and animal sources. Most dietary lipids are triglycerides, composed of glycerol and fatty acids.