The Importance Of The Citric Acid Cycle

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The citric acid cycle, also known as the Krebs cycle and the tribocarboxylic acid cycle, is the hub of the metabolic wheel. The cycle earns this phrase due its role in the oxidation of various fuel molecules i.e. its catabolic nature, and in the provision of carbon skeletons for biosynthesis or its anabolic nature. Anaplerotic reactions are imperative as they replenish the anabolic reactions to ensure the cycle’s function is maintained. The citric acid cycle‘s central role in metabolism is also highlighted through its link to oxidative phosphorylation and the regulatory enzymes that adapt to different nutritional and health conditions.

Aerobic respiration must occur in every living organism as it products are used to
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2). The cycle is broken into eight consecutive stages (Table 1). The first step initiating the cycle involves acetyl CoA reacting with oxaloacetate to first produce citryl CoA and then citrate from further hydrolysis. In the second step, citrate is isomerised into isocitrate. This is achieved through a dehydration and hydration step with cis-Aconistase produced as an intermediate and the aconitase catalysing the overall reaction. The third step involves isocitrate undergoing decarboxylation and oxidation reactions to form alpha-ketoglutarate (Berg J.M et al., 2015). In step four, a second decarboxylation oxidation reaction occurs to form succinyl CoA from alpha-ketoglutarate. Step five involves splitting succinyl CoA to produce succinate and CoA. In step six, succinate is oxidised to fumurate and FADH2 is formed simultaneously (Ness B., 2017). The penultimate step involves fumurate being converted to malate. In the affixing step of the citric acid cycle, malate is oxidised to form oxaloacetate, enabling a cycle to be established (Berg J.M et al., 2015).

The Citric acid cycle has catabolic and anabolic functions. Catabolic is defined as the breakdown of organic molecules and anabolic means essentially the opposite - the synthesis of organic molecules. The citric acid cycle is used as an energy source for oxidative phosphorylation and has a role in the metabolic pathways of lipids, carbohydrates and proteins. These functions and links will be explored further in this
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The catabolic role the cycle plays involves the degradation of products and reactants involved in the cycle to produce ATP. This function appears to be the salient function of the cycle. The citric acid cycle is the final pathway for the oxidation of carbohydrates, lipids and proteins due to the use in amino acids metabolism (Cox M.M et al.,2017). Acetyl CoA has an amphibolic role. It fulfils its catabolic role by entering the citric acid cycle for the breakdown of amino acids. The catabolism of amino acids provides succinate, oxaloacetate, fumarate and alpha-ketoglutarate. These products are then utilized for the anabolic nature of the cycle. Hence why, the citric acid cycle is the hub of the metabolic wheel as the molecules produced through amphibolic reactions are vital for metabolism in the body. Catabolic reactions are also important for harvesting high energy electrons (Berg J.M et al.,
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