Triacylglycerols , also

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... 

The simplest lipids constructed from fatty acids are the triacylglycerols, also referred to as triglycerides, fats, or neutral fats. Triacylglycerols are composed of three fatty acids each in ester linkage with a single glycerol (Fig. 10-2). Those containing the same kind of fatty acid... 

Structure and Triacylglycerols (also called fats or triglycerides) consist of three fatty acid function chains esterified to a glycerol backbone. Simple triacylglycerols have three... 

This chapter examines the biosynthesis of three important components of biological membranes—phospholipids, sphingolipids, and cholesterol (Chapter 12). Triacylglycerols also are considered here because the pathway for their synthesis overlaps that of phospholipids. Cholesterol is of interest both as a membrane component and as a precursor of many signal molecules, including the steroid hormones progesterone, testosterone, estrogen, and cortisol. The biosynthesis of cholesterol exemplifies a fundamental mechanism for the assembly of extended carbon skeletons from five-carbon units. 

In this process, an oil (triacylglycerol, also known as triglyceride) molecule reacts with a molecule of water, releasing a molecule of fatty acid (12), commonly known as free fatty acid (FFA), and a molecule of diacylglycerol (DG, also called diglyceride). The reaction scheme is shown below ... 

Lipids may be polar or nonpolar (amphipathic). Polar lipids have limited solubility in water because they are amphipathic, i.e., they possess hydrophilic and hydro-phobic regions in the same molecule. Major polar lipids include fatty acids, cholesterol, glycerophosphatides, and glycosphingolipids. Very short chain fatty acids and ketone bodies are readily soluble in water. Nonpolar lipids serve principally as storage and transport forms of lipid and include triacylglycerols (also called triglycerides) and cholesteryl esters. 

Fats are lipids composed of triacylglycerols (also called triglycerides). A triacyl-glycerol molecule contains 3 fatty acids esterified to one glycerol moiety (Fig. 1.6). 

Adipose tissue triacylglycerols also contain fatty acids synthesized in the liver, principally from excess calories ingested as glucose. The pathway of fatty acid synthesis generates palmitate, which can be elongated to form stearate, and unsaturated to form oleate. These fatty acids are assembled into triacylglycerols and transported to adipose tissue as the lipoprotein VLDL (very-low-density lipoprotein). 

A few fatty acids with trans double bonds (trans fatty acids) occur naturally, but the major source of trans fats comes from partial hydrogenation of vegetable oils in, for example, the preparation of margarine. The same catalysts that catalyze the hydrogenation of the double bonds in a triacylglycerol also catalyze their stereoisomerization. The mechanism for conversion of a cis to a trans double bond follows directly from the mechanism of catalytic hydrogenation (see Section 6.1) once one realizes that all of the steps in the mechanism are reversible. 

These long chain aliphatic carboxylic acids are essential parts of most lipids in foods including triacylglycerols (also referred to as triglycerides) and phosphoglycerides (also referred to as phospholipids). Fatty acids can be either saturated or unsaturated (Figure 1). The fatty acids of major vegetable oils and animal fats include saturated, monounsaturated and polyunsaturated fatty acids (Table 1). 

In a triacylglycerol, also known as fat or oil, the hydroxyl groups on the trialcohol glycerol form ester bonds with the carboxyl groups of three fatty acids. For example, glycerol and three molecules of stearic acid form a triacylglycerol. 

In the body, fatty acids are stored as triacylglycerols, also called triglycerides, which are triesters of glycerol (a trihydroxy alcohol) and fatty acids. The general formula of a triacylglycerol follows ... 

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