THE GREAT METABOLIC RACE
Throughout one hour run, there are numerous biochemical reactions occur inside the body. These reactions are parts of metabolism and all of the reactions rely on Adenosine Triphosphate (ATP) through the break down of carbohydrates and fats. ATP acts as a main currency which provides free energy to synthesize the macromolecules, movement of muscle and solutes transportation. Carbohydrates and fats are main energy source in our body however fats provide more energy per unit weight. This essay focuses on the metabolic pathways including the roles and the structures of carbohydrates and fats within the body of the athlete in one hour.
During digestion, carbohydrates and fats are stored in liver as glycogen and adipose tissue as triglycerides. When resting, muscles used triglycerides to maintain when needed. When the muscles carry out heavier activity, anaerobic pathways are required to provide quick energy. In aerobic condition, pyruvate is converted to lactate which is called fermentation reaction. After fermentation reaction, two ATP are formed.
After 5 minutes of running, 85% of energy was supplied by carbohydrates and 15% from fats. Glucose storage located in liver and muscles, while liver regulates blood glucose, muscles are responsible for movement and require much more energy. Glycogen is a form of polysaccharide which has highly-branched structure. At this early stage, the first process of glucose catabolism is called glycolysis takes place. Glycolysis occurs in cytosol of the cell, each glucose molecule enters glycolysis, 2 ATP are produced. Glycolysis consists of 2 phases: preparatory phase and payoff phase with 10 steps. Preparatory phase begins with the phosphorylation of glucose into glucose-6-phosphate which catalysed by hexokinase. This first reaction is exergonic and require the conversion of ADP to ATP. After phosphorylating, phosphohexose isomerase catalysed the isomerization of glucose-6-phosphate to fructo-6-phosphate. In step 3, phosphofructokinase-1 phosphorylates fructose-6-phosphate into fructose-1,6-bisphosphate. This reaction is exergonic reaction and the first committed step in glycolysis. The subsequent step fructose-1,5-biphosphate is cleaved into glyceraldehyde 3-phosphate and dihydroxyacetone phosphate by aldolase. After that, dihydroxyacetone phosphate converts into glyceraldehyde-3-phosphate which is the end product of preparatory phase. In general, the preparatory phase uses 2 ATP and form ADP. Payoff phase starts with the oxidation and phosphorylation of two glyceraldehyde 3-phosphate and two inorganic phosphate group and form two 1,3-Biphosphoglycerate. In this reaction, oxidising form of NAD+ being reduced to form NADH which can be converted to ATP. Via phosphoglycerate kinase, 1,3-phosphoglycerate converted to 3-phosphoglycerate which first ATP is made. Through the phosphate transfer and dehydration, two moles of phosphoenolpyruvate are formed and have higher energy compared to 2-phosphoglycerate which is the product during phosphate transfer. Pyruvate kinase catalysed the last step to form 2 moles of pyruvate and 2 ATP. Overall, 2 pyruvate, 2 ATP and 2 NADH are formed during glycolysis.
Half way through the race, 50% of energy was supplied by carbohydrates and 50% from fats. Both of these catabolism reactions undergo aerobic pathway.