Lipid Metabolism

Lipids are a heterogeneous group of water-insoluble compounds that are soluble in organic solvents. Besides being an important constituent of the diet, lipids have many other uses. A great diversity of lipids occurs in nature, and it is very important to get the right kind of lipids in your diet. Lipids are among the biomolecules required for the structure and functions of the cell. Since they are mostly stored in the seeds or fruits of some plants, these are the main sources for obtaining dietary lipids. Studying diversity and the metabolism of lipids is important. A brief introduction to the diversity in structure and functions of lipids is taken in this chapter, along with learning about the classification and nomenclature of fatty acids. The chapter includes the pathways, roles of enzymes, and organelles involved in lipid metabolism. Studying the catabolism of lipids is significant in germinating fatty seeds since they have primarily oils as their storage form. In fatty seeds, the stored lipids are not the source of energy directly. Lipids are metabolized to produce soluble forms of sugars in the storage organs, which are translocated to the meristematic regions in the growing seedlings. A study of pathways, enzymes, and organelles involved in lipid metabolism in germinating seeds is also included in the chapter. Though there is a similarity in the lipid metabolism of plants and animals, a great degree of disparity also exists. In plants, lipid metabolism is more complex and involves many cell organelles. Fatty acid synthesis and oxidation occur in different subcellular locations, involve different metabolic pathways, and involve different sets of enzymes. There is the successive removal of two carbon units as acetyl-CoA during the oxidation of fatty acids. Elongation of the hydrocarbon chain also requires, at the time of fatty acid synthesis, the addition of two carbons at a time. However, precursors for fatty acid synthesis are three carbon compounds, malonyl-CoA, except one acetyl-CoA, which is required as a primer. The condensation reaction is coupled with the simultaneous release of one carbon as carbon dioxide (CO2) (Fig. 10.1).