Triacylglycerols

Triacylglycerols isolated from the hexane extracts account for 2 to 6% of dry biomass in the A race 14), Analysis by reversed-phase HPLC 

TAGS in the adipose tissue serve as the main energy store of the body as well as carriers of fatty acids in lipoproteins. TAGs are also found in the cytoplasmic lipid droplets present in cells of many tissues. 

Besides ESI, chemical ionization (Cl or APCI) has been used for TAG analysis. In Cl in the negative ion mode [75], ionization takes place via abstraction of a proton to 

---

Fats and oils are naturally occurring mixtures of triacylglycerols also called triglyc erides They differ m that fats are solids at room temperature and oils are liquids We generally ignore this distinction and refer to both groups as fats... 

Triacylglycerols arise not by acylation of glycerol itself but by a sequence of steps m which the first stage is acyl transfer to l glycerol 3 phosphate (from reduction of dihy droxyacetone 3 phosphate formed as described m Section 25 21) The product of this stage IS called a phosphatidic acid... 

Hydrolysis of the phosphate ester function of the phosphatidic acid gives a diacylglycerol which then reacts with a third acyl coenzyme A molecule to produce a triacylglycerol... 

Section 26 4 Phospholipids are intermediates in the biosynthesis of triacylglycerols from fatty acids and are the principal constituents of the lipid bilayer component of cell membranes... 

A synthesis of triacylglycerols has been described that begins with the substance shown... 

Triacylglycerol (Section 26 2) A derivative of glycerol (12 3 propanetnol) m which the three oxygens bear acyl groups denved from fatty acids... 

Animal fats and vegetable oils are triacylglycerols, or triesters, formed from the reaction of glycerol (1,2, 3-propanetriol) with three long-chain fatty acids. One of the methods used to characterize a fat or an oil is a determination of its saponification number. When treated with boiling aqueous KOH, an ester is saponified into the parent alcohol and fatty acids (as carboxylate ions). The saponification number is the number of milligrams of KOH required to saponify 1.000 g of the fat or oil. In a typical analysis, a 2.085-g sample of butter is added to 25.00 ml of 0.5131 M KOH. After saponification is complete, the excess KOH is back titrated with 10.26 ml of0.5000 M HCl. What is the saponification number for this sample of butter ... 

Esters of glycerol, called glycerol triesters, triacylglycerols, or triglycerides, are abundant natural products. The most important group of glycerol triesters includes those in which each acyl group is unbranched and has 14 or more carbon atoms. 

All three acyl groups in a triacylglycerol may be the same, all three may be different, or one may be different from the other two. 

Figure 26.2 shows the structures of two typical triacylglycerols, 2-oleyl-l,3-distearylglycerol (Figure 26.2a) and tristearin (Figure 26.2b). Both occur naturally—in cocoa butter, for example. All three acyl groups in tristearin are stearyl (octadecanoyl) groups. In 2-oleyl-l,3-distearylglycerol, two of the acyl groups are stearyl, but the one...

Strictly speaking, the term fatty acid is restricted to those carboxylic acids that occur naturally in triacylglycerols. Many chemists and biochemists, however, refer to all unbranched carboxylic acids, irrespective of their origin and chain length, as fatty acids. 

What fatty acids are produced on hydrolysis of 2-oleyl-1,3-distearylglycerol What other triacylglycerol gives the same fatty acids and in the same proportions as 2-oleyl-1,3-distearylglycerol ... 

Phosphatidic acids not only are intennediates in the biosynthesis of triacylglycerols but also are biosynthetic precursors of other members of a group of compounds called phosphoglycerides or glycerol phosphatides. Phosphorus-containing derivatives of lipids are known as phospholipids, and phosphoglycerides are one type of phospholipid. 

Outline a series of reactions suitable for the preparation of a triacylglycerol of the type illustrated in the equation, where R and R are different. 

High density lipoprotein (HDL) (a-lipoprotein) Triacylglycerols, phospholipids, cholesterol 75... 

Acylglycerols can be hydrolyzed by heating with acid or base or by treatment with lipases. Hydrolysis with alkali is called saponification and yields salts of free fatty acids and glycerol. This is how soap (a metal salt of an acid derived from fat) was made by our ancestors. One method used potassium hydroxide potash) leached from wood ashes to hydrolyze animal fat (mostly triacylglycerols). (The tendency of such soaps to be precipitated by Mg and Ca ions in hard water makes them less useful than modern detergents.) When the fatty acids esterified at the first and third carbons of glycerol are different, the sec-... 

FIGURE 8.3 Triacylglycerols are formed from glycerol and fatty acids. 

Polar Bears Use Triacylglycerols to Survive Long Periods of Fasting... 

Olid carbon is asymmetric. The various acylglycerols are normally soluble in benzene, chloroform, ether, and hot ethanol. Although triacylglycerols are insoluble in water, mono- and diacylglycerols readily form organized structures in water (discussed later), owing to the polarity of their free hydroxyl groups. 

---