Carbon in fatty acids

Pathway of Carbon in Fatty Acid Synthesis Using... 

Triglycerides are the chemical form in which most fat exists in food as well as in the body. A triglyceride is made up of a three-carbon molecule called glycerol, which is bonded to three fatty acids. Fatty acids contain long chains of 12 to 24 carbon atoms. The carbons in fatty acids are bonded to varying numbers of hydrogen atoms. 

There are even numbers of carbons in fatty acids because the acids are built... 

Acyl-CoAs are intermediates in oxidation of fatty acids, in fat synthesis, in elongation of fatty acids longer than palmitate (16 carbons), in fatty acid desaturation. 

Fatty acid methyl esters are currently used in transesterification reactions with sucrose. The formation of methanol, which can be distilled off, drives the estalfication process in favour of the sucrose ester and improves yields. A solvent-less process using a slurry of sucrose and potassium carbonate in fatty acid methyl este or triglycaide oil at 130°C has been developed more recently [5]. 

Figure 5. Thermal oxidation products of saturated fatty acid monohydroperoxide (n=number of carbon in fatty acid moiety).

The milk fat of mammals is very different from the fat depot, particularly in that it contains much higher amounts of triacylglycerols of fatty acids with shorter hydrocarbon chains and lower amounts of triacylglycerols of unsaturated fatty acids (Table 3.8). Characteristic triacylglycerols of milk fat have a number of carbons in fatty acids C44 (7.35%), C42 (7.62%), C34 (6.73%) and C32 (2.92% of total triacylglycerols), which can be used for detection of vegetable and animal fats in milk fat. Other triacylglycerols are C54 (3.32%), C52 (7.76%), C50 (9.97%), 45 (9.09%), (7.91%), C40... 

Dry reduced nickel catalyst protected by fat is the most common catalyst for the hydrogenation of fatty acids. The composition of this type of catalyst is about 25% nickel, 25% inert carrier, and 50% soHd fat. Manufacturers of this catalyst include Calsicat (Mallinckrodt), Harshaw (Engelhard), United Catalysts (Sud Chemie), and Unichema. Other catalysts that stiH have some place in fatty acid hydrogenation are so-called wet reduced nickel catalysts (formate catalysts), Raney nickel catalysts, and precious metal catalysts, primarily palladium on carbon. The spent nickel catalysts are usually sent to a broker who seUs them for recovery of nickel value. Spent palladium catalysts are usually returned to the catalyst suppHer for credit of palladium value. 

Fatty acids Organic acids with long carbon chains. Fatty acids are abundant in cell membranes and are widely used as emulsifiers, as metallic soaps, and for other industrial uses. 

FIGURE 25.1 The citrate-malate-pyruvate shuttle provides cytosolic acetate units and reducing equivalents (electrons) for fatty acid synthesis. The shuttle collects carbon substrates, primarily from glycolysis but also from fatty acid oxidation and amino acid catabolism. Most of the reducing equivalents are glycolytic in origin. Pathways that provide carbon for fatty acid synthesis are shown in blue pathways that supply electrons for fatty acid synthesis are shown in red. 

Lipid Fatty acid components Number of carbon atoms in fatty acid chain... 

Fatty acid flotation method. In this method, the smithsonite was floated using a short carbon chain fatty acid from calcific and dolomitic gangue minerals. The calcite and... 

Biotin is a growth factor for many bacteria, protozoa, plants, and probably all higher animals. In the absence of biotin, oxalacetate decarboxylation, oxalosuccinate carboxylation, a-ketoglutarate decarboxylation, malate decarboxylation, acetoacetate synthesis, citrulline synthesis, and purine and pyrimidine syntheses, are greatly depressed or absent in cells (Mil, Tl). All of these reactions require either the removal or fixation of carbon dioxide. Together with coenzyme A, biotin participates in carboxylations such as those in fatty acid and sterol syntheses. Active C02 is thought to be a carbonic acid derivative of biotin involved in these carboxylations (L10, W10). Biotin has also been involved in... 

Triacylglycerols, commonly refered to as fats and oils, consist of three fatty acids linked to a molecule of glycerol, a three-carbon alcohol. Fatty acids are long-carbon-chain molecules, each with a single carboxyl functional group. Common examples are stearic acid and palmitic acid, shown in Figure 16.3. 

By 1960 it was clear that acetyl CoA provided its two carbon atoms to the to and co—1 positions of palmitate. All the other carbon atoms entered via malonyl CoA (Wakil and Ganguly, 1959 Brady et al. 1960). It was also known that 3H-NADPH donated tritium to palmitate. It had been shown too that fatty acid synthesis was very susceptible to inhibition by p-hydroxy mercuribenzoate, TV-ethyl maleimide, and other thiol reagents. If the system was pre-incubated with acetyl CoA, considerable protection was afforded against the mercuribenzoate. In 1961 Lynen and Tada suggested tightly bound acyl-S-enzyme complexes were intermediates in fatty acid synthesis in the yeast system. The malonyl-S-enzyme complex condensed with acyl CoA and the B-keto-product reduced by NADPH, dehydrated, and reduced again to yield the (acyl+2C)-S-enzyme complex. Lynen and Tada thought the reactions were catalyzed by a multifunctional enzyme system. 

We have briefly noted the role of biotin when we considered the biosynthesis of fatty acids (see Section 15.5). Biotin is a carrier of carbon dioxide and involved in carboxylation reactions. In fatty acid biosynthesis, we noted how acetyl-CoA was... 

The first step is carboxylation of acetyl CoA to malonyl CoA. This reaction is catalyzed by acetyl-CoA carboxylase [5], which is the key enzyme in fatty acid biosynthesis. Synthesis into fatty acids is carried out by fatty acid synthase [6]. This multifunctional enzyme (see p. 168) starts with one molecule of ace-tyl-CoA and elongates it by adding malonyl groups in seven reaction cycles until palmi-tate is reached. One CO2 molecule is released in each reaction cycle. The fatty acid therefore grows by two carbon units each time. NADPH+H is used as the reducing agent and is derived either from the pentose phosphate pathway (see p. 152) or from isocitrate dehydrogenase and malic enzyme reactions. 

The eicosanoids, so called because of their derivation from a 20-carbon unsaturated fatty acid, arachidonic acid (eicosatetraenoic acid), are obtained from membrane phospholipids and synthesized de novo at the time of cellular stimulation. Arachidonic acid is cleaved from membrane-bound phosphatidylcholine by the enzyme phospholipase A2. Alternatively, arachidonic acid may be derived by the sequential actions of phospholipase C and diacylglyceryl lipase. Arachidonic acid can then follow either of two enzymatic pathways that result in the production of inflammatory mediators. The pathway initiated by cyclooxygenase (COX) produces prostaglandins the lipoxygenase pathway generates leukotrienes (Fig. 36.2). 

Fatty acids are carboxylic acids containing an unbranched carbon chain and usually an even number of carbon atoms. Fatty acids do not occur freely in nature, but generally come from esters (esters are discussed later). A few common fatty acids and their sources are shown in Figure 15.12. Fatty acids are important in the production... 

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