GREAT METABOLIC CHALLENGE
Metabolism is a series of vital biochemical processes that take place in order to sustain life. During a marathon run, the individual relies on the breakdown of carbohydrates and lipids, in order to provide energy release in the form of Adenosine Triphosphate (ATP).
This essay will focus on the role of mobilization and structures of both carbohydrates and lipids in the production of ATP.
Mobilization of Carbohydrates
When carbohydrates are consumed during a meal, catabolism originates in the mouth. The salivary enzyme α-amylase breaks down the carbohydrates through the hydrolysis of the α1->4 glycosidic bonds. This is followed by the further breakdown of the complex polysaccharides in the small intestine down to monosaccharides units in order for the glucose to be absorbed directly into the bloodstream.
Mobilization of Lipids
Lipids in the form of triaglycerols are a major source of energy storage. Initially, the lipids are absorbed in the small intestine through emulsification into small droplets by bile salts; thus forming mixed micelles. During low blood sugar levels, the secretion of glucagon and adrenalin hormones activates the release of the enzyme triacylglycerol lipase, which subsequently stimulates the release of fatty acids in adipocytes. The blood protein serum albumin then transports the fatty acid through the bloodstream to tissue such as the renal cortex, heart and skeletal muscle in order to provide energy through β-oxidation.
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Provision of energy during race
On your mark
At the beginning of the race, internal energy laws determine in which direction and to what extent each metabolic reaction will proceed. According to this system, when the Gibbs Free Energy (ΔG) is negative, a spontaneous forward reaction is proceeding towards equilibrium thus resulting in the formation of products from reactants. During this marathon, ATP is the energy currency during the breakdown of macromolecules, more specifically the breakdown carbohydrates and lipids in this case. Furthermore ATP will be necessary for muscular movement and the transport of solutes across biological membranes. 5 minutes
After 5 minutes into the marathon, majority of the energy is being supplied by carbohydrates (85%) specifically glycogen that is stored in skeletal muscle and liver; in comparison to a mere 15% of lipid utilization. At this early stage of the race, the ten-step process of glycolysis is starting to take place; in which pyruvate is being formed from glucose. In the first half of this process known as the preparatory phase, there is a debt of two ATP molecules. However this is recovered in the payoff phase in which 1,3-bisphosphoglycerate is oxidized and phosphorylated to form 3-phosphoglycerate, with the production of four ATP molecules; thus providing a net yield of 2 ATP molecules.
Half way through the race, the citric acid cycle predominates in the oxidation of carbohydrates and lipids in order to supply energy. At this stage, half of the runner’s energy needs are being supplied by carbohydrates while the other half is being met by lipids. Within the mitochondria of the cell,
As the race is nearing the end, most of the energy is being supplied through the catabolism of fats from storages in adipose tissue.