Omega carbon

FIGURE 17-16 The fatty acids in the endoplasmic reticulum. This alternative to /3 oxidation begins with oxidation of the carbon most distant from the a carbon—the oj (omega) carbon. The substrate is usually a medium-chain fatty acid shown here is lauric acid (laurate). This pathway is generally not the major route for oxidative catabolism of fatty acids... 

For nomenclature purposes, the carbonyl carbon of a fatty acid is assigned the number 1. The carbon next to the carbonyl is called the a-carbon (alpha carbon) and the carbon at the opposite end of the chain is called the W-carbon (omega carbon). The pof most fatty acids is around 4,5, so most fatty acids exist in their anion form in the cellular environment. 

The carbon bonded to the a carbon is the p carbon, followed by the y (gamm carbon, the 5 (delta) carbon, and so forth down the chain. The last carbon in the chain is sometimes called the 2 (omega) carbon. 

The last carbon of the chain is called the M-carbon (omega-carbon), so the attached phenyl group is an co-phenyl group, (a) Oxidation of co-phenyl-labeled fatty acids occurs two carbons at a time. Fatty acids having an even number of carbon atoms are degraded to phenyl acetate and "acetate." (b) Oxidation of cophenyl-labeled fatty acids that contain an odd number of carbon atoms yields benzoate and "acetate."... 

FIGURE 8.12 Chemical structure of a-linolenic acid. Although chemists count from the carbonyl carbon (or alpha carbon), physiologists count from the omega carbon. Note that from the omega end, the first double bond appears as the third carbon-carbon bond, hence the name omega-3. ... 

For certain purposes the PUFA are grouped into famihes, based on oleic (n-9-18 l), linoleic (n-6,9-18 2) and a-linolenic (n-3,6,9-18 3) as precursors.The famihes are called omega-9 (co-9), omega-6 (co-6) and omega-3 (double bonds nearest to the omega carbon atom in these acids. Again, n is frequently substituted for (I). Some of the nutritionally important fatty acids are shown in Table 3.1. 

Saturated fatty acids are long-chain carboxylic acids that usually have between 12 and 24 carbon atoms and have no double bonds. Thus, saturated fatty acids are saturated with hydrogen (since double bonds reduce the number of hydrogens on each carbon). Because saturated fatty acids have only single bonds, each carbon atom within the chain has 2 hydrogen atoms (except for the omega carbon at the end that has 3 hydrogens). 

Cold-water frsh like salmon are rich in omega-3 fatty acids, which have a double bond three carbons in from the noncarboxyl end of the chain and have been shown to lower blood cholesterol levels. Draw the structure of 5,8,11,14,17-eicosapentaenoic acid, a common example. (Eicosane = C20H42)... 

Solid-state 13C NMR spectra were obtained on a General Electric Omega PSG 400 spectrometer operating at 100.6 MHz for l3C nuclei using a Doty Scientific 5 mm high speed MAS probe. The various NMR experiments performed in this study are shown schematically in Figure 1. The carbon chemical shift scale (11) and 90 degree... 

Resistance to electron flow is measured in ohm units and is symbolized by the letter R. The ohm unit is symbolized by the Greek letter omega (Q). A resistance slows the movement of electrons in a circuit much like a smaller-diameter pipe would slow the movement of water. While all electronic circuit components have a certain resistance, components known as resistors—components that have a certain defined resistance in ohms, kilohms (kO, or 103 Q), or megaohms (MQ, or 106 Q) and are inserted into circuits for their resistance values—are available. These usually are small, cylindrical epoxy or plastic packages with leads (short wires) protruding from each end and small granules of carbon or resistance wire inside to slow the electrons. Resistors are manufactured with different degrees of accuracy. One percent... 

Prostaglandins are a subgroup of a larger family of compounds known collectively as eicosanoids, which are synthesized from arachidonic acid (arachidonate) this is a 20-carbon omega-6 unsaturated fatty acid (C20 4). The source of the arachidonic acid for PG synthesis is the cell membrane. Most membrane phospholipids have an unsaturated fatty acid as arachidonate at carbon 2 on the glycerol backbone to help maintain membrane fluidity. The arachidonic acid released from the membrane by the... 

Oxidation is a cyclical pathway which removes a C2 (acetyl) unit form the fatty acyl-CoA on each cycle. The designation [3 derives from the traditional system of labelling atoms within fatty acid molecules where the carbon attached to the carboxyl group is a and the methyl carbon is always CO (omega) ... 

There is one nomenclature that is commonly used, particularly in news articles intended for the lay audience. It is useful to understand it. Here families of fatty acids are collected by designating where the first double bond occurs, starting at the methyl group (CH3) end of the molecule, frequently known as the omega (co) carbon atom. Thus, the omega-3 fatty acids look hke ... 

Note that all the double bonds are cis and that the double bond closest to the methyl group end of the molecule begins with carbon atom 3, numbering from the terminal methyl group. Hence EPA is an omega-3 fatty acid. 

The key substrate for synthesis of the eicosanoids is the omega-6,20-carbon fatty acid arachidonic acid ... 

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