The Great Metabolic Race
Throughout a race or marathon, there are many metabolic processes that occurring. In order to sustain the body through a race of one duration, the body utilises two fuels: carbohydrates and fats. These two fuels will be explored in depth throughout this essay, including how they function to provide energy at different points during the race.
In a human diet, the main source of energy is obtained from carbohydrates. All carbohydrates contain the elements carbon, hydrogen and oxygen, with the formula (CH2O)n. Glucose, for example, has the chemical formula C6H12O6. During cellular respiration, glucose is a very important source of energy for cells. When the level of carbohydrates is too low for the body to run on, the energy source switches to fats. Although fats provide approximately twice as much energy as carbohydrates, fats are not the preferred source of energy due to the fact that they are harder. to break down. They are made up of fatty acids, which contain the elements carbon, hydrogen and oxygen. Triglycerides, for example, which make up the majority of fats, consist of a glycerol head and three phosphates, which form the characteristic three tails of the structure.
Before the race begins, the body is at rest. At this stage the body utilises 35% of it’s energy from carbohydrates, and the other 65% from fats, or lipids. At this stage, the body undergoes lipid breakdown through the beta oxidation pathway. Beta oxidation occurs in the mitochondria of all cells excluding red blood cells and ________ cells, as they do not contain mitochondria. The fatty acid chains that enter beta oxidation are broken into two carbon acetic acid fragments. Coenzyme A (CoA) then attaches to the acetic acid fragments, which forms Acetyl CoA. This Acetyl CoA then goes on to enter the Citric Acid Cycle, or the Krebs Cycle.
Within the Citric Acid Cycle, the Acetyl CoA bonds to oxaloacetate, which is a molecule containing four carbons. The CoA group breaks off, forming a molecule with six carbons, known as citrate. Citrate is then converted to isocitrate. Once this occurs, isocitrate is oxidised, producing a molecule of carbon dioxide and alpha ketoglutarate (NAD+ to NADH). The four carbon molecule bonds with Coenzyme A, forming succinyl CoA. The enzyme catalysing this reaction is alpha ketoglutarate dehydrogenase. After this, the CoA group from the succinyl CoA is replaced by a phosphate. This phosphate molecule goes on to participate in the formation of ATP from ADP. In this step, succinate is formed. The succinate is then oxidised, forming fumarate (FAD to FADH2). Water is added, converting fumarate to malate. Finally, the malate regenerates oxaloacetate (NAD+ to NADH).
After a couple of minutes, the body then begins to undergo anaerobic respiration.
Gets energy from stored ATP, lipids
By five minutes into the race, the ATP stores that the body was partially relying on at the commencement of the race have all but dissipated. The body then switches its main source of fuel to carbohydrates; at this point, the body is sourcing 85% of its energy needs from carbohydrates, and the remaining 15% from fats.
The anaerobic pathway continues for a time, but as the body begins to settle into a steady rhythm, it shifts towards an aerobic pathway. First, glycogenolysis occurs. Glycogenolysis is the breakdown of glycogen to glucose, which will later be used in glycolysis.
Glycogen phosphorylase is a key enzyme in the process of glycogenolysis. With the aid of another enzyme known as pyridoxical phosphate, glucose residues are cleaved sequentially, producing glucose-1-phosphate (phosphorolysis). This continues to occur on the non-reducing ends of the branches until it reaches a glucose molecule four units from the end. This is known as the outer limit of the limit dextrin. Following this, ?-(1,4)-glucan-6-glycosyltransferase removes three of the four units from the four-glucose branch, leaving one glucose unit. Then, amylo-?-(1,6)-glucosidase, also known as the debranching enzyme, hydrolysed the ?-(1,6)-glycosidic bond, with which the single glucose unit is attached to the chain. This releases glucose, as well as a chain of ?-(1,4)-linked glucose units, which are not branched. With the branch removed, the enzyme glycogen phosphorylase is able to continue to cleave the glucose residues. Through this phosphorylation, as well as through hexokinase, glucose-6-phosphate is formed. This reaction is exergonic, with a negative Gibbs free energy value (ATP to ADP). Phosphohexokinase isomerase goes on to isomerise this glucose-6-phosphate molecule, producing fructose-6-phosphate. Unlike the previous reaction, this reaction is endergonic, and has a positive Gibbs free energy value. Although this favours the backwards reaction, the exergonic property of the previous reaction as well as the following reaction outweigh the endergonic property of this reaction.
It is now that glycolysis occurs. Glycolysis is a ten step process, essentially aiming to convert glucose to pyruvate.
The first step of glycolysis
ATP stores are running out
Body uses carbohydrates instead
Describe gluconeogenesis (“… in a process known as gluconeogenesis. …the glycogen can then go on to enter into glycolysis…*mention parts of the body involved, eg. liver and muscle and how they are involved.*)