Discuss about the Yield of ATP Molecules per Glucose Molecule.
Below is the calculation for the yield of ATP from 4 moles of glucose in the liver. The calculation is based on the yield of ATP from the oxidation of a unitary mole of glucose. The calculation involved is based on the synthesis of a variable amount of ATP. As we know, the synthesis of ATP in the liver gives the maximum yield and this has been done under optimal conditions (Flurkey, 2010).
At first the glucose in transformed into G6Pase consuming 1 molecule ATP. Parallel, Fructose ^ phosphate is transformed into 1, 6-biphosphate consuming another molecule of ATP. BPG obtained from transformation of glyceraldehydes 3 phosphate
BPG -> 3- phosphoglycerate = 2 Molecules of ATP
Phosphoenolpyruvaye transformed to pyruvate -> 2 Molecules of ATP
The pryruvate is transformed into reaction of acetyl CoA with carbon dioxide producing NADH.
Succinyl CoA is transformed into succinate -> 2 Molecules of ATP
The NADH produced in the pathway yields the following
2/3 Molecules per NADH -> 4/6 for 2 cytoplasmic NADH
Pyruvate Oxidation -> 3 molecules per NADH = 6 ATP molecules
2 molecules ATP per FADH x 2 FADH = 4 Molecules of ATP
3 molecules of ATP per NADH ( Krebs cycle) x 3 NADH = 18 molecules of ATP.
Total yield per mol of glucose = 38
Yield for 4 mol of input = 38 x 4 = 152
Glucose is metabolized in the human body and the primary form of storage in the body is glycogen which is found in the liver and the skeletal muscles of the body. There is a difference between the amounts of ATP production with the variation of site of metabolism (Hackmann and Firkins, 2015). The ATP synthesis will not take place in the muscle tissue. The liver is responsible for the maintenance of the optimum level of glucose in the blood stream. At the last step of the gluconeogenesis, the G6Pase catalyses the synthesis and governs the release of the glucose in the bloodstream (Ncbi.nlm.nih.gov, 2016). However, muscle tissue do not participate in glucose export hence they lack the G6Pase enzyme.
The oxidation process of the fuel molecules in the body namely amino acids, fatty acids and carbohydrates are completed through the process of the citric acid cycle. Acetyl Coenzyme A is the basic form of input of the fuel molecules in the cycle. This is the final pathway of oxidation and after transamination every amino acid enters this cycle. While entering the process are completely oxidized in the process (Qu, Lee and Boos, 2004). The carbohydrates input in this stage are in the form of pyruvate and acetyl coA. If there is any surplus of carbohydrates in the food intake of the body, these are transformed to neutral fat at this stage. The neutral fat thus produced does not take part in any metabolism activity but are stored in the adipose tissue. Many of these amino acids are converted so that they can take part in the gluconeogenesis through OAA. In addition to this, in this cycle, the fat is completely disintegrated and the net synthesis of carbohydrates from the fat is zero in this cycle. Most of the pathways are either catabolic or anabolic in nature (Taylor and Robinson, 2005). However, this is the only true pathway that is completely amphibolic in nature. The anaplerotic role of the cycle ensures that the concentration of 4 carbon units is maintained in the cells.
The molecule of GTP is not an equivalent molecule of ATP but the when the GTP is gathered in a triphospate group, the amount of energy built up is equivalent to the triphosphate group of ATP. Additionally, GTP has the ability of a phosphoral group into ADP to form an ATP. Hence, the GTP is considered equivalent to ATP.
ATP formation in the liver is through glycolysis which is a non aerobic process. This process breaks down the glucose into 3C compounds, pyruvate and lactate thereby forming ATP. Further in the process, the pyruvate dehydrogenase transforms the 3C compounds into 2C compound with the extraction and release of carbon di oxide (Zou, Ma and Wang, 2015). This is through the pathway of the citric acid cycle.
The overall equation is represented as follows
The preliminary step in the formation of ATP is the transformation of glucose in the blood into the cells. AT this step 4 ATPs and 2NADH are produced.
AT the next step, the pyruvate is oxidized in the mitochondria producing 2 ATPs and 8NADH as well as 2FADH2 .
Hence the total number of molecules generated in the process is as follows
6 Carbon dioxide molecules.
This way, 12 ATP is produced from one molecule input in the citric acid cycle.
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Flurkey, W. (2010). Yield of ATP Molecules per Glucose Molecule. J. Chem. Educ., 87(3), pp.271-271.
Hackmann, T. and Firkins, J. (2015). Electron transport phosphorylation in rumen butyrivibrios: unprecedented ATP yield for glucose fermentation to butyrate. Front. Microbiol., 6.
Ncbi.nlm.nih.gov. (2016). National Center for Biotechnology Information. [online] Available at: https://www.ncbi.nlm.nih.gov/ [Accessed 17 Jul. 2016].
Qu, Q., Lee, S. and Boos, W. (2004). Molecular and biochemical characterization of a fructose-6-phosphate-forming and ATP-dependent fructokinase of the hyperthermophilic archaeon Thermococcus litoralis. Extremophiles, 8(4).
Taylor, R. and Robinson, R. (2005). Quinoxaline Synthesis from α-Hydroxy Ketones via a Tandem Oxidation Process Using Catalysed Aerobic Oxidation. Synlett, (6), pp.1003-1005.
Zou, H., Ma, W. and Wang, Y. (2015). A novel process of dye wastewater treatment by linking advanced chemical oxidation with biological oxidation. Archives of Environmental Protection, 41(4).