Great Race

During exercise, a range of metabolic actions occur to sustain the human body. During a race, different fuels are used at different time points in order for the runner to derive the energy needed during the exercise. During the Great Metabolic Race, the runner utilises two different types of fuel at three different time points. These are fats and carbohydrates. The main energy base that is used by the body is ATP. ATP, or Adenosine Triphosphate, is a nucleotide which contains high amounts of chemical energy. This stored energy is released when the molecule is broken down into ADP, or Adenosine Diphosphate.

At time point zero, which is at the start of the race before the runner has commenced running, fats are used as fuel. Fats are triglycerides that are derived from fatty acids and glycerols. The structure of a triglyceride shows that there is a glycerol backbone, with three fatty acid tails joined to this backbone. Different fatty acids contain different numbers of hydrogen and carbon atoms, which represent the properties of that particular molecule of fat. The carbon atoms in the fat molecule form an uneven chain, with the more carbon atoms present, the longer the chain. Fatty acids that contain long chains are more affected by van der Waals forces which raise its melting point. Van der Waals forces represent the number of attractive or repulsive forces between molecules. In addition, long chains of fatty acids yield a greater amount of energy when metabolised.

Fats play an important role in providing energy for the body. Fats are more reduced than carbohydrates and they can store more energy per unit weight. Fats contain approximately 37.8 kilojoules of energy per gram. The body can also store more fat cells than glycogen. Fats are broken down in the body to release free fatty acids and glycerol, and the released glycerol is converted to glucose. The glucose produced is used as the energy source.

The fatty acid chains of the triglyceride are broken up two carbons at a time. The broken down carbons are then formed into a two carbon acetyl sugar via the process of a beta oxidation reaction. After this, they are broken down via the Citric Acid Cycle. However, to avoid the situation of the body having to break down a large amount of acetyl sugars at once, some of these acetyl sugars are turned into ketone bodies. The third and final step in the catabolism of fatty acids involves the transfer of electrons from the carriers to the electron transport chain.

The beta oxidation is the pathway in which fatty acids are broken down to produce acetyl CoA as well as NADH and FADH2. There are four reactions which take place in the beta oxidation pathway; dehydrogenation, hydration, oxidation and finally thiolysis. Dehydrogenation involves the enzyme Acyl-CoA-Dehydrogenase catalysing the production of a double bond between the second and third carbon. Hydration is the next step, where the bond between the second and third carbon is hydrated, which only forms the L isomer. Oxidation refers to the oxidation of L-Beta-hydroxyacyl CoA via NAD+. This reaction turns the hydroxyl group into a keto group. The fourth and final step is the cleavage of beta-ketoacyl CoA by the thiol group if coenzyme A. This group is then placed in between the second and third carbon. At the end on the beta oxidation pathway, there is a yield of 14 ATP, 1.5 of which are from FAD2, 2.5 from NADH, and 10 ATP from acetyl CoA.

The Citric Acid Cycle involves a series of reactions to produce energy via the oxidation of acetate from carbohydrates, proteins and in this case, fats, into carbon dioxide.

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