Omega-bonding

Vitadur Omega Bonded-to-metal porcelain Vita Zahnfabrik, Bad Sackingen, Germany... 

The unsaturated fatty acids, linoleic [60-33-3] and linolenic [463-40-17, contain two and three double bonds and are considered beneficial components of the diet. The double bond is an essential ingredient for human nutrition when it is in the correct position on the fat molecule. Humans are unable to insert the double bond at the omega-3 and -6 position. Therefore, fatty acids containing double bonds at these positions are essential in the diet, including linoleic and linolenic acids. They are accordingly described as essential fatty acids (EFA) (23). 

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)... 

An exopeptidase that does not cleave standard peptide bonds. An example is pyroglutamyl-peptidase I (MEROPS C15.010), which releases an N-terminal pyroglutamyl from hormones such as thyrotropinreleasing hormone and luteinizing hormone. Omega peptidases are included in Enzyme Nomenclature subsubclass 3.4.19. 

Ge, J., Liu, W., Dong, S. (1987) Determination of partition coefficient with chemically bonded omega-hydroxysilica as HPLC column packing. Sepu 5, 182-185. 

The characteristic properties of peptides result from the presence of a chain of several or many amide bonds. A first problem is that of numbering, and here Fig. 6.1 taken from the IUPAC-IUB rules may help. A second and major aspect of the structure of peptides is their conformational behavior. Three torsion angles exist in the backbone (Fig. 6.2). The dihedral angle co (omega) describes rotation about C-N,

rotation about N-C , and ip (psi) describes rotation about C -C. Fig. 6.2 represents a peptide in a fully extended conformation where these angles have a value of 180°. 

The omega (<0) numbering system is also used for unsaturated fatty acids. The co-family describes the position of the last double bond relative to the end of the chain. The omega designation identifies the major precursor fatty add, e.g., arachidonic add is formed from linoleic acid (co-6 family). Arachidonic acid is itself an important precursor for prostaglandins, thromboxanes, and leukotrienes. 

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. 

Note that arachidonic acid differs from EPA only in that the latter has one additional double bond near the methyl end of the molecule. Arachidonic acid is an omega-6 fatty acid. 

Figure 11.9 Structures of three omega-3, three omega-6 and one omega-9 polyunsaturated fatty adds. The structure of a hydrocarbon chain is sometimes presented in this manner, where each peak or trough represents a CHj group except at a double bond which links CH groups.

The major omega-3 fatty acid in hsh oil is eicosapentae-noic acid, which contains hve double bonds compared with only four present in the omega-6 fatty acid, arachidonic acid. When eicosapentaenoic acid is substrate for eico-sanoid production, it gives rise to prostacyclins and thromboxanes of the three series (Figure 22.9(a)) whereas when arachidonic acid is substrate, it gives rise to the two series, thromboxane A2 and prostacyclin I2. Thromboxane A3 has... 

The effect of dietary fats on hypertriglyceridemia is dependent on the disposition of double bonds in the fatty acids. Omega-3 fatty acids found in fish oils, but not those from plant sources, activate peroxisome proliferator-activated receptor-alpha (PPAR- ) and can induce profound reduction of triglycerides in some patients. They also have antiinflammatory and antiarrhythmic activities. In contrast, the omega-6 fatty acids present in vegetable oils may cause triglycerides to increase. 

FIGURE 7-19 Conformation at the glycosidic bonds of cellulose, amylose, and dextran. The polymers are depicted as rigid pyranose rings joined by glycosidic bonds, with free rotation about these bonds. Note that in dextran there is also free rotation about the bond between C-5 and C-6 (torsion angle [Pg.251]

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