Lipids as energy stores

1 INTRODUCTION MANY PLANTS AND ANIMALS NEED TO STORE ENERGY FOR USE AT A LATER TIME. LIPID FUELS ARE MAINLY TRIACYLGLYCEROLS OR WAX ESTERS 

This chapter is about storage lipids in general, but because of their predominance as a fuel and their importance in biochemistry, the discussion will largely be concerned with the triacylglycerols. 

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Roles Fatty acids have four major biological roles 1. They are components of membranes (glycerophospholipids and sphingo- lipids) 2. Several proteins are covalently modified by fatty acids 3. They act as energy stores (triacylglycerols) and fuel molecules 4. Fatty acid derivatives serve as hormones and intracellular second messengers. 

Pelagic arctic animals have adapted to strong seasonality by storing large amounts of lipids as energy reserves. The proportion of lipid to dry body mass... 

Lipids are involved in a number of essential processes in the growth and reproduction of marine invertebrates. Membrane lipids, primarily phospholipids and sterols, combine with membrane proteins to form insoluble complexes that are important in membrane structure. Many marine invertebrates have oil droplets within cells of hepatic-type tissues. These droplets are primarily triacylglycerols or wax esters and serve as energy stores. Finally, lipids occur in water-soluble lipoproteins where phospholipids, triacylglycerols, and sterols are combined with various apoproteins. Lipids are transported between various tissues via hemolymph lipoproteins. Female-specific lipoproteins occur in the hemolymph and eggs of adult females of many marine invertebrates. These egg lipoproteins provide protein and lipid for the development of larvae after they hatch from the... 

Triacylglycerols are the major energy-storing lipids, whereas phosphoglycerols, sphingomyelin, and gly-cosphingolipids are amphipathic and have structural functions in cell membranes as well as other specialized roles. 

The various roles of fats were summarised in the introduction to this chapter. Two questions arise from this what is the advantage of storing lipid as the major energy reserve Why are there three lipid fuels in the blood while there is only one carbohydrate fuel ... 

Lipids are a class of biomolecules defined by the fact that they are insoluble in water and similar solvents. Lipids include the fats in foods and the fats stored in our bodies, waxes, and steroids. Importantly for the body, the membranes that surround all cells are made of lipids. Like the carbohydrates starch and glycogen, lipids also serve as energy storage compounds, but per gram, lipids contain more than twice as much energy as carbohydrates and proteins. Excess nutrients not needed for energy are stored as body fat. 

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