Malonyl-S-ACP

Now starts the first of many similar cycles. Acctyl-S-ACP condenses (4) with malonyl-S-ACP to give a four-carbon chain. 

Butyroyl-S-ACP now reacts with a second molecule of malonyl-S-ACP and proceeds through reactions 3-6 to form hexanoyl-S-ACP, etc., until palmitoyl-S-ACP is formed. 

H2O -H CH3CH = CHCO-S-ACP acetyl S-ACP + HS-E - acetyl-S-E -h ACP-SH acetyl-S-E -H malonyl-S-ACP... 

A similar long arm is apparent in biotin (7.9), again enzyme bound through a lysine residue. The coenzyme (7.9) assists in the carboxylation of acetyl-CoA 1.8) with carbon dioxide yielding malonyl-CoA 1.14). Exchange of both acetyl-CoA and malonyl-CoA occurs with acyl carrier proteins (AGP) having free thiol groupings. Condensation then occurs between acetyl-S-ACP and malonyl-S-ACP with simultaneous decarboxylation the carboxylate anion is transferred into the new bond (Scheme 1.2) [6]. Subsequent steps involve reduction, dehydration and double-bond saturation. They... 

The biosynthesis of fatty acids is accomplished two carbons at a time by an enzyme complex called fatty acid synthetase. The biochemical reactions involved in fatty acid synthesis are described in Special Topic E WileyPLUS). Each of these biochemical reactions has a counterpart in synthetic reactions you have studied. Consider the biochemical reactions involved in adding each —CH2CH2— segment during fatty acid biosynthesis (those in Special Topic E that begin with acetyl-S-ACP and malonyl-S-ACP, and end with butyryl-S-ACP). Write laboratory synthetic reactions using reagents and conditions you have studied (not biosynthetic reactions) that would accomplish the same sequence of transformations (i.e., the condensation-decarboxylation, ketone reduction, dehydration, and alkene reduction steps). 

Ql. Acetyl-S-ACP to malonyl-S-ACP to stearic acid, desaturated to oleic acid, chain extended by three acetate units to a C24 unsaturated acid, and decarboxylation gives (Z)-9-tricosene. 

The malonyl-S-ACP then condenses with a primer fatty acid molecule which must also be attached to a molecule of ACP. The simplest... 

But)rryl-S-ACP may then condense with malonyl-S-ACP in a reaction analagous with eqn. 60 above when repetition of reactions 61, 62 and 63 will result in the production of propionyl-S-ACP. Thus each complete repetition of the s)rstem described above results in the addition of two carbon atoms to the primer fatty acid until eventually a long chain fatty acid may be built up. 

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