The Great Metabolic Race
The Great Metabolic Race Introduction (The comparison of fuels) Carbohydrates and fats are the main energy reserves in the human body. When carbohydrates and fats are metabolised during digestion, they are stored in the liver as glycogen and in adipose tissue as triglycerides, respectively. Glycogen is a chain of glucose residues that branch out to form more polymers. In contrast, triglycerides are esters that are comprised of 2-3 fatty acid chains connected to a glycerol. Compared with carbohydrates, the body can reduce lipids more intensely, thus lipids can store more energy per unit weight. The difference in structure and energy storage between the two fuels allows the body to sustain enough energy for the 45 minute marathon.
Beginning At rest, the muscles use triglycerides to acquire the energy they need. However, when the body carries out more strenuous exercise, the muscles acquire its energy via anaerobic respiration.
5 minutes When the body is 5 minutes into the race, it will acquire 85% of its energy from carbohydrates, and 15% from fats. This means that glucose will be the main source for acetyl-CoA that will enter the citric acid cycle. In order for this to occur, the body will mobilise glucose from glycogen stores in the muscle and liver.
Glycogen mobilisation: Glycogen mobilisation in the muscles supply immediate energy to the muscle cells. In contrast, glycogen mobilisation in the liver supplies energy for other cells in the body. Glycogen mobilisation requires glycogen phosphorylase to remove the terminal glucose on the upper branch of glycogen. The terminal glucose is dispensed as glucose-1phosphate, which is later converted into glucose-6-phosphate by phosphoglucomutase. This conversion allows it to enter glycolysis. The removal of glucose continues until 4 residues remain before a branching point is met. The next 3 glucose residues are cleaved together and placed on the lower glycogen branch. The last residue at the branching point is then freed as glucose. Glycogen phosphorylase will continue to remove glucose residues on the lower branch, and they, too, will be dispensed as glucose-1-phosphate molecules, and later converted into glucose-6phosphate.
Glycolysis: Glycolysis occurs in the cytosol of the cell, outside the mitochondria. This biochemical pathway serves to convert glucose molecules into pyruvates. For each glucose molecule that enters glycolysis, 2 ATP are produced.
Glycolysis consists of 2 stages and 10 different reactions. The first 5 reactions that make up the preparatory phase collaborate to convert glucose into glyceraldehyde-3phosphate. The last 5 reactions that make up the payoff phase collaborate to convert glyceraldehyde-3-phosphate into pyruvate. Preparatory Phase: This process requires in input of 2 ATP. Reaction 1: Hexokinase phosphorylates glucose into glucose-6-phosphate, by removing OH on glucose and replacing it with the phosphate from ATP. Here, ΔG°’= -16.7kJ/mol. Reaction 2: Phosphohexose Isomerase converts glucose-6-phosphate into fructose-6- phosphate. Here, ΔG°’= +1.7kJ/mol. Reaction 3: Phosphofructokinase-1 phosphorylates fructose-6-phosphate into fructose-1,6 bisphosphate. Another ATP molecule is consumed and ΔG°’= -14.2kJ/mol. Reaction 4: Aldolase cleaves fructose-1,6-bisphosphate to form dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. Here, ΔG°’= +23.8kJ/mols. Reaction 5: Triose Phosphate Isomerase converts dihydroxyacetone phosphate into glyceraldehyde-3- phosphate. Here, ΔG°’= +7.5kJ/mol. The preparatory phase uses 2 ATP to form 2 ADP. The glyceraldehyde-3- phosphate continues into the payoff phase to finally be converted into pyruvate.
Beginning At rest, the muscles use triglycerides to acquire the energy they need. However, when the body carries out more strenuous exercise, the muscles acquire its energy via anaerobic respiration.
5 minutes When the body is 5 minutes into the race, it will acquire 85% of its energy from carbohydrates, and 15% from fats. This means that glucose will be the main source for acetyl-CoA that will enter the citric acid cycle. In order for this to occur, the body will mobilise glucose from glycogen stores in the muscle and liver.
Glycogen mobilisation: Glycogen mobilisation in the muscles supply immediate energy to the muscle cells. In contrast, glycogen mobilisation in the liver supplies energy for other cells in the body. Glycogen mobilisation requires glycogen phosphorylase to remove the terminal glucose on the upper branch of glycogen. The terminal glucose is dispensed as glucose-1phosphate, which is later converted into glucose-6-phosphate by phosphoglucomutase. This conversion allows it to enter glycolysis. The removal of glucose continues until 4 residues remain before a branching point is met. The next 3 glucose residues are cleaved together and placed on the lower glycogen branch. The last residue at the branching point is then freed as glucose. Glycogen phosphorylase will continue to remove glucose residues on the lower branch, and they, too, will be dispensed as glucose-1-phosphate molecules, and later converted into glucose-6phosphate.
Glycolysis: Glycolysis occurs in the cytosol of the cell, outside the mitochondria. This biochemical pathway serves to convert glucose molecules into pyruvates. For each glucose molecule that enters glycolysis, 2 ATP are produced.
Glycolysis consists of 2 stages and 10 different reactions. The first 5 reactions that make up the preparatory phase collaborate to convert glucose into glyceraldehyde-3phosphate. The last 5 reactions that make up the payoff phase collaborate to convert glyceraldehyde-3-phosphate into pyruvate. Preparatory Phase: This process requires in input of 2 ATP. Reaction 1: Hexokinase phosphorylates glucose into glucose-6-phosphate, by removing OH on glucose and replacing it with the phosphate from ATP. Here, ΔG°’= -16.7kJ/mol. Reaction 2: Phosphohexose Isomerase converts glucose-6-phosphate into fructose-6- phosphate. Here, ΔG°’= +1.7kJ/mol. Reaction 3: Phosphofructokinase-1 phosphorylates fructose-6-phosphate into fructose-1,6 bisphosphate. Another ATP molecule is consumed and ΔG°’= -14.2kJ/mol. Reaction 4: Aldolase cleaves fructose-1,6-bisphosphate to form dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. Here, ΔG°’= +23.8kJ/mols. Reaction 5: Triose Phosphate Isomerase converts dihydroxyacetone phosphate into glyceraldehyde-3- phosphate. Here, ΔG°’= +7.5kJ/mol. The preparatory phase uses 2 ATP to form 2 ADP. The glyceraldehyde-3- phosphate continues into the payoff phase to finally be converted into pyruvate.
