The Great Metabolic Race Biology Essay


Adenosine Triphosphate is a ribonucleotide 5-triphosphate that functions as a phosphate group donor in metabolism. ATP carries chemical energy between metabolic pathways by serving as a shared intermediate coupling endergonic and exergonic reactions within the body. During exercise, ATP is required to fuel the body's energy demands. Therefore in the form of a hypothetical race, this essay will explain how energy is utilised during exercise.

At the beginning of the race, even at rest before running, energy is being used to fuel normal metabolic functions. According to the "Runner's Energy Graph" at time zero, carbohydrates supply 35% of the energy and fats supply 65% of the energy. During metabolism, the body maintains a balance between catabolic (exergonic) and anabolic (endergonic) reaction pathways. Energy coupling then occurs, the use of exergonic reactions to produce endergonic reactions. Due to the sum of energy change (ΔG). Exergonic reactions produce a negative ΔG, while endergonic reactions produce a positive ΔG. When coupled, the overall ΔG is negative and therefore producing an exergonic reaction.

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The race has started and after 5 minutes, anaerobic pathways are required to provide quick energy. According to the "Runner's Energy Graph" at time 5 minutes, carbohydrates is at its highest peak supplying 85% of the energy and fats are at its lowest peak supplying 15% of the energy. Glycolysis plays a vital role in anaerobic metabolic processes. It involves ten reactions by which glucose is oxidised to 2 molecules of pyruvate.

The first five steps is the preparatory phase wherein energy is consumed which allows glucose to be converted to 2 molecules of glyceraldehyde-3-phosphate. Firstly, by transferring a phosphate group from ATP to glucose causes the phosphorylation of the hydroxyl group of carbon 6 (C-6), to form glucose-6-phosphate. Secondly, the aldohexose glucose-6-phosphate is converted to fructose-6-phosphate. This time at

C-1 and using 1 mole of ATP, fructose-6-phosphate is again phosphorylated to form fructose 1,6 biphosphate. In the fourth reaction, fructose 1,6 biphosphate is cleaved to form dihydroxyacetone phosphate and glyceraldehyde 3-phosphate. During the fifth reaction, isomerisation occurs between glyceraldehyde 3-phosphate, forming 2 molecules of glyceraldehyde 3-phosphate. This ends the preparatory phase with an overall consumption of 2 ATP.

The last five step is the payoff phase wherein energy is produced which causes 2 molecules of glyceraldehyde 3-phosphate to be converted into 2 molecules of pyruvate. In the sixth reaction, the 2 molecules of glyceraldehyde 3-phosphate is phosphorylated by inorganic phosphate (Pi) and oxidised by NAD+ reducing it to NADH, forming 2 molecules of 1,3 biphosphoglycerate. During the seventh reaction, 1,3 biphosphoglycerate is converted to 2 molecules of 3-phosphoglycerate and releasing 2 mole of ATP. The eighth reaction involves isomerisation of both of the 3-phosphoglycerate to form 2 molecules of 2-phosphoglycerate. In the ninth reaction, the 2 molecules of 2-phosphoglycerate is dehydrated to form 2 molecules of

2-phosphoenolpyruvate. Finally, during the tenth reaction, there is a transfer of a phosphate group to ADP to form pyruvate. This ends the glycolysis stage and overall yields the production of 2 ATP.


Approximately at 30 minutes, the body begins using equal amounts of carbohydrates and fats, to provide aerobic energy to maintain the runner's pace. According to the "Runner's Energy Graph" at time 30 minutes, both carbohydrates and fats are equal, providing 50% of energy. The Citric Acid Cycle or Krebs Cycle is essential for oxidation of both carbohydrates and lipids under aerobic conditions.

It consists of eight steps, firstly with the condensation of acetyl-CoA and oxaloacetate form citrate. Secondly, citrate is converted to isocitrate. Thirdly, isocitrate undergoes oxidation and decarboxylation to produce α-ketoglutarate. Fourthly, α-ketoglutarate undergoes further oxidation and decarboxylation to form succinyl-CoA. In the fifth reaction, coupled reactions allow the formation of succinate. During the sixth reaction, succinate is oxidised to form fumarate. Fumarate is then hydrated in the seventh step to produce malate. Finally in the eighth reaction, malate is oxidised by NAD+ to form oxaloacetate with an overall yield of 1 ATP.


Approximately 40 minutes into the race, most of the body's energy is being supplied by catabolising fats. According to the "Runner's Energy Graph" at time 40 minutes, carbohydrates is supplying 45% of the energy and gradually decreasing and fats supplying 65% of the energy and gradually increasing. The β-oxidation pathway occurs in the mitochondria.

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It involves a cyclic repetition of a four step process in which fatty acids are converted into acetyl-CoA. Firstly, the carbon chain between the alpha and beta carbons are oxidised to form trans-Δ2-Enoyl-CoA. Secondly, the carbon-carbon double bond of trans-Δ2-Enoyl-CoA becomes hydrated to produce L-β-Hydroxy-acetyl-CoA. Thirdly, L-β-Hydroxy-acetyl-CoA becomes oxidised to form a ketone, β-Ketoacyl-CoA. The final reaction consists of the catalysed by thiolase, producing Acyl-CoA and

Acetyl Co-A. Then six more passes through the pathway yield seven more molecules of acetyl-CoA, the seventh arising from the last two carbon atoms of the 16-carbon chain. Therefore, eight molecules of acetyl-CoA is formed. Overall the 7 cycles of

β-oxidation of fatty acids yields 98 ATP.


In conclusion, during exercise the body undergoes different metabolism pathways in order to produce an efficient amount of energy.