TCA cyde

Examine Figure 5.1 again. There is an apparent conflict if dtric add accumulates there would appear to be no way in which the TCA cyde could continue to regenerate oxaloacetate. On the other hand continuation of the TCA cyde would regenerate oxaloacetate but there will be correspondingly less dtric add accumulated. 

The answer is that not only is there no apparent regeneration of oxaloacetate there is seemingly no way of producing any of the TCA cyde intermediates from sucdnyl CoA through to oxaloacetate. 

In addition to dtrate, there are other addic intermediates of file TCA cyde and several of these are used in industry. Even though some have been produced by fermentation, production is currently from other, cheaper sources. 

It was originally thought that microbial fermentation by Aspergillus terreus followed a similar pattern in that dtric add - produced by glycolysis plus the bridging reaction and two Dathwavs rst reaction of the TCA cyde - was converted to aconitic add. This compound was... 

Give three reasons why it is believed that the formation of itaconic add in A. terreus is via a route which does not involve TCA cyde intermediates. 

The nitrogen source in the medium is the amino add glutamate. There are several cations K Mn2, Cn2, Zn2, Mg2, Co2, Fe2, Ca2 Mo6. Phosphate (POi") is the major anionic component. Fumaric add is a TCA cycle intermediate and may improve metabolic balance through the catabolic pathways and oxidation through the TCA cyde. Peptone may improve growth through the provision of growth factors (amino acids, vitamins, nudeotides). 

Succinic add source of carbon and energy improves metabolic balance between carbon flux from glucose and oxidation throgh TCA cyde. 

The citric acid cycle, also called the Krebs cycle or the tricarboxylic add (TCA) cyde, is in the mitochondria. Although oxygen is not directly required in the cyde, the pathway will not occur anaerobically because NADH and FADH will accumulate if oxygen is not available for the electron transport chain. 

In the reaction that bridges glycolysis and die TCA cyde, for each pyruvate degraded to acetyl CoA, one CO2 is released and a further NAu is reduced to NADH + H. ... 

Rgure 5.1 A simplified diagram of glycolysis arxJ the tricarboxylic add (TCA) cycle showing the entry points for various substrates. Indicates the two reactions specific to the glyoxylate cycle. Compounds in boxes are potential substrates for entry into the TCA cyde, via at l CoA. 

A large intracellular pool of a) ions (caused by a negative effect of severe limitation of b) on protein turnover) and an increased respiratory activity, which in part is not coupled to c) synthesis, stimulates metabolic flux throu glycolysis without significant metabolic control. This, togettier with d) pyruvate carboxylase and the peculiarities in the operation of the TCA-cyde, results in elevat cellular concentrations of e>. This in turn enhances dtric add accumulation by inhibiting i) dehydrogenase. 

Exopolysaccharide production ntay be improved by tiie provision of various organic con xments, otiier Aan the main carbon and energy source. These can improve growth of the production organism (growth factors) and/or directly enhance the synthesis of exopolysaccharide. Additions that improve polymer yield include tricarboxylic add (TCA) cyde intermediates, which are thou t to improve metabolic balance between carbon flow frcnn carbohydrate substrate through the catabolic pathwaj arul oxidation through the TCA cyde. 

Acceptable answers to part 1) indude amino adds and fatty adds or specific examples of each, such as glycine or stearic add respectively. The obvious answer for part 2) is tiie central metabolite pyruvate, though all of tiie adds of the TCA cyde would be appropriate. Answers to part 3) include the prindpal add of the hexose monophosphate... 

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