Biological Sciences
Triglycerides
Triglycerides are a type of lipid molecule composed of three fatty acids attached to a glycerol backbone. They serve as a major form of energy storage in the body and are found in adipose tissue. Triglycerides are also important for insulation, protection, and the transportation of dietary fats within the body.
Written by Perlego with AI-assistance
Related key terms
1 of 5
9 Key excerpts on "Triglycerides"
- J.E. Vance, Dennis E. Vance(Authors)
- 1991(Publication Date)
- Elsevier Science(Publisher)
D.E. Vance and J. Vance (Eds.) Biochemistry oflipids, Lipoproteins and Membranes 0 1991 Elsevier Science Publishers B.V. All rights reserved. 171 CHAPTER 6 Metabolism of triacylglycerols DAVID N. BRINDLEY Department of Biochemistry, Lipid and Lipoprotein Research Group, 328 Heritage Medical Research Centre, University of Alberta, Edmonton, Alta., Canada I. Introduction Triacylglycerols play a major role in energy storage in animals, where they are depos- ited in adipose tissue. When this storage is excessive it is manifested as obesity, and there is considerable medical interest in trying to understand why some people are so prone to this condition, whereas others find it equally difficult to gain weight. In plants, the storage of triacylglycerols is best illustrated by the oil seeds, in which the triacylglycerols provide energy for growth. These seeds constitute very important commercial crops. Triacylglycerols are ideally suited to this storage function because of the highly reduced state of their fatty acids. Triacylglycerols have high energy con- tents - about 37 kJ/g, compared with 17 kJ/g for protein and 16 kJ/g for carbohy- drate, including glycogen, which is also used to store energy in mammals. The other advantange of the triacylglycerols is their insolubility in water, which means that they do not alter the osmotic pressure of the cell. Most of the triacylglycerols in animals are stored in adipose tissue. However, tria- cylglycerolscan be deposited in liver, heart, and skeletal muscle under several condi- tions of metabolic stress when the supply of fatty acids from adipose tissue exceeds the need, or capacity of the cells to oxidize them. The formation of triacylglycerols removes the potentially toxic effects of excess fatty acids and acyl-CoA esters which could damage membranes and inhibit enzymes. The process of triacylglycerol synthe- sis also regenerates CoA.
No longer available |Learn more- Sharon Rady Rolfes, Kathryn Pinna, Ellie Whitney(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
Fat refers to the class of nutrients known as lipids. The lipid family includes Triglycerides (fats and oils), phospholipids, and sterols. Triglycerides are most abundant, both in foods and in the body. The following sections describe the similarities and differences among the remarkably diverse members of the lipid family. 1 5 The Lipids: Triglycerides, Phospholipids, and Sterols Copyright 2018 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. WCN 02-300 134 Chapter 5 5-1 The Chemist’s View of Fatty Acids and Triglycerides LEARN IT Recognize the chemistry of fatty acids and Triglycerides and differ-ences between saturated and unsaturated fats. Like carbohydrates, lipids are composed of carbon (C), hydrogen (H), and oxygen (O). Because lipids have many more carbons and hydrogens in proportion to their oxygens, they can supply more energy per gram than carbohydrates can (Chapter 7 provides details). The many names and relationships in the lipid family can seem overwhelming— like meeting a friend’s extended family for the first time. To ease the introductions, this chapter first presents each of the lipids from a chemist’s point of view using both words and diagrams. Then the chapter follows the lipids through digestion and absorption and into the body to examine their roles in health and disease. For people who think more easily in words than in chemical symbols, this preview of the upcoming chemistry may be helpful: 1. Every triglyceride contains one molecule of glycerol and three fatty acids (basically, chains of carbon atoms). 2. Fatty acids may be 4 to 24 (even numbers of) carbons long, the 18-carbon ones being the most common in foods and especially noteworthy in nutrition. 3. Fatty acids may be saturated or unsaturated. Unsaturated fatty acids may have one or more points of unsaturation—that is, they may be mono unsatu-rated or poly unsaturated.
eBook - PDF- H. Stephen Stoker(Author)
- 2015(Publication Date)
- Cengage Learning EMEA(Publisher)
8-4 Energy-Storage Lipids: Triacylglycerols L E A R N I N G F O C U S Be familiar with general structural representations for a triacylglycerol; distinguish between simple and mixed triacylglycerols and between fats and oils. With the notable exception of nerve cells, human cells store small amounts of energy-providing materials for use when energy demand is high. The most widespread energy-storage material within cells is the carbohydrate glycogen (Section 7-15); it is present in small amounts in most cells. Lipids known as triacylglycerols also function within the body as energy-storage materials. Rather than being widespread, triacylglycerols are concentrated primarily in special cells (adipocytes) that are nearly filled with the material. Adipose tissue containing these cells is found in various parts of the body: under the skin, in the abdominal cavity, in the mammary glands, and around various organs (Figure 8-4). Triacylglycerols are much more efficient at storing energy than is glycogen because large quantities of them can be packed into a very small volume. These energy-storage lipids are the most abundant type of lipid present in the human body. In terms of functional groups present, triacylglycerols are triesters; three ester functional groups are present. Recall from Section 5-11 that an ester is a compound produced from the reaction of an alcohol with a carboxylic acid. The alcohol involved in triacylglycerol formation is always glycerol, a three-carbon alcohol with three hydroxyl groups. CH 2 O A A CH O CH 2 O Glycerol OH OH OH Fatty acids are the carboxylic acids involved in triacylglycerol formation. In the esterification reaction producing a triacylglycerol, a single molecule of glycerol reacts with three fatty acid molecules; each of the three hydroxyl groups present is esterified. Figure 8-5 shows the triple esterification reaction that occurs between glycerol and Copyright 2016 Cengage Learning.
eBook - PDF- Carter Litchfield(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
1 INTRODUCTION The vital role of Triglycerides in human life and activities is familiar to almost all who read these lines. Triglycerides are a major form of energy storage for both plants and animals. Man draws upon these sources to provide fatty foods for himself and to obtain fats and oils as industrial raw materials. To better understand these biosynthetic, metabolic, and technological processes involving Triglycerides, chemists have developed numerous analytical techniques for characterizing complex triglyceride mixtures. Two factors make the analytical chemistry of natural fat Triglycerides exceptionally difficult: (i) the extremely large number of possible molecu-lar species (Section I,B)> and (ii) the very similar chemical and physical properties of most of these molecules. Using the classical techniques of fractional crystallization and permanganate oxidation, only simple separa-tions of groups of Triglycerides were possible, and most analyses were semi-quantitative in nature. Between 1956 and 1965, however, a series of new chromatographic and enzymatic techniques revolutionized the field, and many of the earlier difficulties have now been overcome. With this pro-liferation of analytical methods, the former question, Can I analyze for XYZ triglyceride content? has now changed to, Which method should I use to analyze for XYZ triglyceride content? The purpose of this monograph is to provide a comprehensive and criti-cal review of the entire field of triglyceride analysis so that the reader can select the best technique or techniques for solving his own specific problem. By devoting an entire book to the subject at a time when the field has reached considerable maturity, triglyceride analysis can now be viewed 1 2 1. INTRODUCTION with a broader perspective than was possible in earlier review papers (186,240,365,494,550,585,700,898,909).
eBook - PDFHandbook of Food Analysis
Volume 1: Physical Characterization and Nutrient Analysis
- Leo M.L. Nollet(Author)
- 2004(Publication Date)
- CRC Press(Publisher)
10 Analysis of Neutral Lipids: Triacylglycerols J. S. Perona and V. Ruiz-Gutierrez Instituto de la Grasa, CSIC, Seville, Spain I. INTRODUCTION A. Triacylglycerols Triacylglycerols (TAGs) are complex molecules pre-sent in all oils and fats. They mainly serve as energy stores, but they are also employed as carriers of fatty acids within aqueous solutions such as blood. TAGs are made up of three fatty acids, attached to a glyc-erol backbone by an ester linkage. The wide variety of fatty acids that may attach to the glycerol back-bone generates the large diversity of TAGs that can be found. The fat stores of both plant and animal organisms are formed by mixtures of TAGs, the fatty acids containing from four to 36 carbon atoms, with up to six double bonds. Each of these fatty acids are combined in triplets to form TAGs that share very similar physicochemical properties, thus making their separation and analysis difficult. The length of the hydrocarbon chains of the fatty acids and the location of the double bonds within the TAG molecule is ordered and determines the spatial configuration, and therefore, the physical properties of the molecule. TAGs that contain a higher proportion of unsaturated fats and fewer carbon atoms are more polarized. Regardless of the saturated fatty acids (SFAs), most of the monounsaturated fatty acids (MUFAs) have the double bond situated between carbons C9 and C10 ( 9 ). With respect to the poly-unsaturated fatty acids (PUFAs), the double bond is often located between carbons C12 and C15. These double bonds are not naturally conjugated, but rather a methyl group normally remains between them. Although most frequently the fatty acid double bonds are found in the cis configuration, some natural processes and industrial procedures may transform these bonds into trans .
eBook - PDFNutrition
Science and Applications
- Lori A. Smolin, Mary B. Grosvenor(Authors)
- 2016(Publication Date)
- Wiley(Publisher)
They can be used to produce small amounts of ATP or form glucose. 4 4 H 2 O ADP Citric acid cycle OH O 8 Acetyl–CoA C C C C C C C C C C C C C C C C Fatty acid (palmitic acid) H H H C C H H O CoA CoA + 8 e – H S C C C Acetyl–CoA C C CoA H + H + 1 Fatty acid β β β β FIGURE 5.14 Providing energy from Triglycerides The breakdown of Triglycerides yields fatty acids and a small amount of glycerol. Fatty acids provide most of the energy stored in a triglyceride molecule. 5.5 Lipid Functions in the Body 169 stored; then, between meals, some of the stored Triglycerides will be broken down to provide energy. When the energy in the diet equals the body’s energy requirements, the net amount of stored triglyceride in the body does not change. Feasting When energy is ingested in excess of needs, the excess can be stored as fat in adipose tissue. Excess energy consumed as fat is packaged in chylomicrons and transported directly from the intestines to the adipose tissue. Because the fatty acids in our body fat come from the fatty acids we eat, what we eat affects the fatty acid composition of our adi- pose tissue; therefore, if you eat more saturated fat, there will be more saturated fat in your adipose tissue. Excess energy consumed as carbohydrate or protein must first go to the liver, where the carbohydrate and protein can be used, although inefficiently, to synthesize fatty acids; these fatty acids are then assembled into Triglycerides, which are transported to the adipose tissue in VLDLs. Lipoprotein lipase at the membrane of cells lining the blood vessels breaks down the tri- glycerides from both chylomicrons and VLDLs so that the fatty acids can enter the cells, where they are reassembled into Triglycerides for storage (Figure 5.15). The ability of the body to store fat is theoretically limitless. Adipocytes can increase in weight by about 50 times, and new adipocytes can be synthesized when existing cells reach their maximum size (see Chapter 7).
eBook - PDF- Ira Wolinsky, Judy A. Driskell, Ira Wolinsky, Judy A. Driskell(Authors)
- 2004(Publication Date)
- CRC Press(Publisher)
This chapter provides a brief overview of fatty acid, triglyceride and glyc-erol metabolism under normal dietary circumstances. Also included is a discussion on the dietary and supplemental sources of MCT and glycerol. Finally, this chapter reviews human studies that have investigated MCT and glycerol as ergogenic aids. Note that the terms MCT and LCT used through-out the chapter refer to triglyceride molecules composed primarily of MCFA and LCFA, respectively, while recognizing that some LCFA are present in MCT and some MCFA are present in LCT. II. Overview of Metabolism A. Chemical and Physical Properties All Triglycerides have the same chemical structure of three fatty acids attached to a glycerol molecule through ester bonds (Figure 14.1). Most fatty acids in nature exist as Triglycerides, although free fatty acids are formed during normal metabolism. Triglyceride molecules found in nature may contain the same fatty acid species at all three positions, or they may contain different fatty acids. The unique physical and chemical properties of tri-glycerides are thus defined by the characteristics of the fatty acids. Table 14.1 shows some common fatty acids found in nature and are categorized as having short, medium or long hydrocarbon chains. The division between lauric (12:0) and myristic (14:0) acid is somewhat arbitrary; some literature sources list lauric acid as a LCFA or myristic acid as a MCFA, while other sources refer to lauric and myristic acid as neither MCFA nor LCFA, but rather “in between.” Nevertheless, the classification of fatty acids according to chain length is useful because the groupings reflect certain metabolic attributes unique to each group. Note that increased chain length is generally associated with increased melting point and decreased solubility in water. 1,2 Also note that the presence of double bonds in the LCFA is associated with Medium-Chain Triglycerides and Glycerol 223 decreased melting point.
eBook - PDF- Glenn R. Gibson, Marcel Roberfroid, Glenn R. Gibson, Marcel Roberfroid(Authors)
- 2008(Publication Date)
- CRC Press(Publisher)
180 Cholesterol Metabolism ......................................................... 182 Synthesis and Uptake of Cholesterol by Cells ......................... 182 References ......................................................................... 186 Triacylglycerols (TAGs) and cholesterol are quantitatively the most important circulating lipids. Both have important physiological roles and abnormalities in their metabolism are implicated in major pathologies such as obesity, insulin resistance, type 2 diabetes, dyslipidemia, and atherosclerosis. This chapter will present an overview of TAG metabolism and of its regulation 163 164 Handbook of Prebiotics with emphasis on intra-cellular metabolism and on recent findings. For cho-lesterol, the chapter focuses mainly on the mechanisms of cholesterol entry into and exit out of the cells and of the organism. General Presentation Triacylglycerols are one of the main forms of transport of energy in the cir-culation from one tissue to another. They are also the main energy stores of the body. They have two origins, dietary intake, which is by far the more important source in humans, and endogenous synthesis. The main sites of endogenous synthesis from glycerol-3-phosphate (G3P) and fatty acids are liver and adipose tissue. Most fatty acids used for this synthesis are provided by breaking down other TAGs while de novo lipogenesis (DNL), the synthesis of new molecules of fatty acids from nonlipid substrates, is a minor path-way. G3P can be provided by phosphorylation of glycerol by glycerol kinase (liver), by glycolysis or glyceroneogenesis (liver and adipose tissue). The main site of storage of TAGs, by far, is white adipose tissue. However, small amounts are stored in other tissues such as liver, heart, and muscles and excessive accumulation of lipids in these tissues can contribute toward the development of insulin-resistance.
eBook - PDF- Ji-Xin Cheng, Xiaoliang Sunney Xie, Ji-Xin Cheng, Xiaoliang Sunney Xie(Authors)
- 2016(Publication Date)
- CRC Press(Publisher)
19 .2 Lipid Droplets as a Conserved Energy Storage Lipid droplets are cytoplasmic bodies comprising mainly of triacylglycerols (TAGs) and sterol esters (Martin and Parton 2006). TAG is an evolutionarily conserved source of energy formed by the ester bonds between a glycerol and three fatty acids. The hydro-phobic packing of the TAG fatty acid chains provides a compact and anhydrous means of energy storage. The energy yield of fatty acid catabolism is 9 kcal/g, which is more than twice the energy yield of 4 kcal/g of carbohydrates, the next high-energy mole-cule in biological systems (Voet and Voet 2010). In addition, the packing of anhydrous fatty acids provides more energy per storage mass as compared to hydrous packing. For example, 1 g of glycogen, the carbohydrate energy storage form, can be hydrated with 2 g of water, which reduces the energy yield per gram to 1.33 kcal. Thus, for the same stor-age mass, fatty acids provide greater than sixfolds more energy than carbohydrates. The efficient means of energy storage is conserved from yeast to human where excess energy is converted to fatty acids and TAG and stored as cytoplasmic lipid droplets. 19 .3 Lipid Droplets as a Dynamic Organelle As energy storage depots, lipid droplets represent a dynamic pool of TAG that expands with nutritional excess and shrinks with starvation. However, since their initial descrip-tion in the nineteenth century, lipid droplets were mostly viewed as simple inert and immobile energy depots whose structures and functions were sparsely characterized. In recent decades, lipid droplets are increasingly recognized as a dynamic organelle that participates in critical cellular processes including energy metabolism, vesicle traffick-ing, and signaling (Guo et al. 2009).
Index pages curate the most relevant extracts from our library of academic textbooks. They’ve been created using an in-house natural language model (NLM), each adding context and meaning to key research topics.
