LIPIDS ARE INSOLUBLE IN WATER

Termites digest glucose produced by cellulose-digesting microorganisms living in the termites digestive tract. 

---

Fat absorbed from the diet and lipids synthesized by the liver and adipose tissue must be transported between the various tissues and organs for utilization and storage. Since lipids are insoluble in water, the problem of how to transport them in the aqueous blood plasma is solved by associating nonpolar lipids (triacylglycerol and cholesteryl esters) with amphipathic hpids (phospholipids and cholesterol) and proteins to make water-miscible hpoproteins. 

Since nonpolar lipids are insoluble in water, for transport between the tissues in the aqueous blood plasma they are combined with amphipathic lipids and proteins to make water-miscible lipoproteins. 

Lipids are transported between membranes. As indicated above, lipids are often biosynthesized in one intracellular membrane and must be transported to other intracellular compartments for membrane biogenesis. Because lipids are insoluble in water, special mechanisms must exist for the inter- and intracellular transport of membrane lipids. Vesicular trafficking, cytoplasmic transfer-exchange proteins and direct transfer across membrane contacts can transport lipids from one membrane to another. The best understood of such mechanisms is vesicular transport, wherein the lipid molecules are sorted into membrane vesicles that bud out from the donor membrane and travel to and then fuse with the recipient membrane. The well characterized transport of plasma cholesterol into cells via receptor-mediated endocytosis is a useful model of this type of lipid transport. [9, 20]. A brain specific transporter for cholesterol has been identified (see Chapter 5). It is believed that transport of cholesterol from the endoplasmic reticulum to other membranes and of glycolipids from the Golgi bodies to the plasma membrane is mediated by similar mechanisms. The transport of phosphoglycerides is less clearly understood. Recent evidence suggests that net phospholipid movement between subcellular membranes may occur via specialized zones of apposition, as characterized for transfer of PtdSer between mitochondria and the endoplasmic reticulum [21]. 

Lipids Class of biomolecules that includes fats and oils all lipids are insoluble in water and similar substances. 

Lipids are insoluble in water and an interfacial tension therefore exists between the phases when lipids are dispersed (emulsified) in water (or vice versa). This tension in toto is very large, considering the very large interfacial area in a typical emulsion (section 3.7). Owing to the interfacial tension, the oil and water phases would quickly coalesce and separate. However, coalescence (but not creaming) is prevented by the use of emulsifiers (surface active agents) which form a film around each fat globule (or each water... 

In exploring the biological role of lipids in cells and tissues, it is essential to know which lipids are present and in what proportions. Because lipids are insoluble in water, their extraction and subsequent fractionation require the use of organic solvents and some techniques... 

After synthesis on the smooth ER, the polar lipids, including the glycerophospholipids, sphingolipids, and glycolipids, are inserted into specific cellular membranes in specific proportions, by mechanisms not yet understood. Membrane lipids are insoluble in water, so they cannot simply diffuse from their point of synthesis (the ER) to their point of insertion. Instead, they are delivered in membrane vesicles that bud from the Golgi complex then move to and fuse with the target membrane (see Fig. 11-23). Cytosolic proteins also bind phospholipids and sterols and transport them between cellular membranes. These mechanisms contribute to the establishment of the characteristic lipid compositions of organelle membranes (see Fig. 11-2). 

By definition, lipids are insoluble in water. Yet they exist in an aqueous environment, and their behavior toward water is therefore of critical importance biologically. 

These lipids are insoluble in water and are classified on the basis of their ultracentrifugal properties into chylomicrons, very low-density lipoprotein (VLDL), intermediate-density lipoprotein (IDL), low-density lipoprotein (LDL) and high-density lipoprotein (HDL) in order of ascending density. Table 2.4 gives the classification and roles of lipoproteins. 

A biological compound that contains a large proportion of C—H bonds and less oxygen than in carbohydrates is called a lipid. Fats, oils, and waxes are aU lipids. Lipids are insoluble in water and soluble in nonpolar organic solvents. In general, lipids that are derived from animals are called fats, and plant lipids are called oils. Lipid molecules are found in... 

Lipids are insoluble in water and this profoundly affects the particular phenomena associated with their digestion, absorption, transport in the blood, and metabolism at the cellular level. Fat is easily recognized when it accumulates within the body, but the chemical and technical definition of fats and hpids are more difficult. Of nutritional interest are triacylglycerols (TAG), phospholipids (PL), sterols, and some derived lipids — results of the hydrolysis or enzymatic breakdown of simple and compound lipids. 

I ipids are a broad class of biomolecules. Although strucnirally diverse, all J-F lipids are insoluble in water because each lipid molecule contains a large number of nonpolar hydrocarbon units. In this section we discuss two important types of lipids fatS9.nA steroids. 

To conclude this review we will breifly mention the conformation of (Lys)jj in lipid solutions. These lipids are associated with membranes and lipoproteins. We will illustrate the effect of two phosphoglycerides, which consist of a glycerol backbone, two fatty acid chains and a phosphorylated alcohol (Figure 10). These lipids are insoluble in water but... 

LIPIDS ARE A HETEROGENEOUS group of naturally occurring organic compounds, classified together on the basis of their common solubility properties. Lipids are insoluble in water, but soluble in relatively nonpolar aprotic organic solvents, including diethyl ether, dichloromethane, and acetone. 

In particular, lipids are insoluble in water but are soluble in nonpolar organic solvents, such as diethyl ether. Lipids can be extracted from cells and tissues by organic solvents. This solubility property distinguishes lipids from three other major classes of natural products—carbohydrates, proteins, and nucleic acids—which in general are not soluble in organic solvents. 

---