Energy is needed by living organisms to perform work in their daily life. In plants, energy originates from the Sun as light energy and converted to carbohydrate, fat and protein while in human beings and animals, energy originates from the source of food through Krebs cycle. Krebs cycle is defined as “a central part of the energetic metabolism that contributes to the generation of ATP by the chemical breakdown of carbohydrates, fats and proteins. It is a series of chemical reactions catalysed by enzymes occurring in the inside of mitochondria called the matrix and which can be disposed circularly” (Nazaret, Heiske, Thurley, & Mazat, 2008, p. 455).There are eight important steps involving in the process of Krebs cycle in metabolism namely condensation, isomerisation, first oxidative decarboxylation, second oxidative decarboxylation, synthesis of succinyl-CoA, oxidation of succinate, hydration of carbon double bond and lastly, regeneration of oxaloacetate (refer to Figure 1 in Appendix 1).
In the first step in process of Krebs cycle in metabolism is the condensation reaction. The condensation process is “the acetic acid subunit of acetyl coenzyme A (acetyl-CoA) strips off the CoA portion from acetyl-CoA” (Tortora, Funke, & Case, 2010, p. 128). The remaining two carbons are combined with the oxaloacetate which is four carbons to form a molecule of citrate which is six carbons molecule. In this process, the acetyl coenzyme A acts only as a transporter of acetic acid from one enzyme to another. This is because the coenzyme is released by hydrolysis from the molecule so that it combines with another acetic acid molecule to begin the Krebs cycle again (Reece, Urry, Cain, Wasserman, Minorsky, & Jackson, 2011).
The citric acid molecule undergoes an isomerisation of citrate in the second step in the process of the Krebs cycle in metabolism. Reece et al. (2011) defined isomer as “The isomer is one of several compounds with the same molecular formula but different structures and therefore different properties. There are three types of isomers are structural isomers, cis-trans isomers, and enantiomers” (p. 108). During this process, the hydroxyl group and a hydrogen molecule are removed from the citric structure in the formed of the water molecule (H2O). In the same time, the two carbons form a double bond between the molecules. Next, the water molecule is added back in the process. Then, the hydroxyl group and hydrogen molecule are reversed with the respect to the original structure of the citric molecule (Reece et al., 2011). Thus, the isocitrate is formed.
The third step in the process of Krebs cycle in metabolism is the first oxidative decarboxylation. This reaction involved the enzyme Aconitase act as a catalyst (Caret, Denniston, & Topping, 1997). Besides, Blei and Odian (1999) claimed that the citrate is synthesised undergoes condensation which removes a water molecule to become cis-Aconitate. The reaction is followed by the hydration of...