Exercise Science: Glucose Catabolism and Energy Production Cycles

This assignment delves into the intricate processes by which the human body generates ATP from glucose catabolism. It meticulously outlines the three primary energy cycles: glycolysis, the Krebs cycle (also known as the citric acid or tricarboxylic acid cycle), and beta-oxidation. The assignment provides a detailed step-by-step breakdown of each cycle, including the raw materials involved, the enzymatic reactions, and the end products generated. Glycolysis is explained from the conversion of glucose to pyruvate, including the role of enzymes like hexokinase and phosphofructokinase. The Krebs cycle is described with its sequential steps, starting from acetyl CoA and oxaloacetate to the production of NADH, FADH2, and GTP. Beta-oxidation is detailed with its stages of fatty acid breakdown. The assignment also discusses the body's preference for utilizing free fatty acids over carbohydrates as a fuel source, highlighting the higher energy content of fats. Furthermore, it explains why protein is typically not the primary fuel source unless necessary, due to its complex tertiary structure and lower energy content. The assignment concludes with a comprehensive reference list.

Running head: EXERCISE SCIENCE
EXERCISE SCIENCE
Name of the student:
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1EXERCISE SCIENCE
Identify the 3 main energy processes/cycles that the human body utilizes to produce
ATP from catabolizing 1 molecule of glucose.
The three main energy cycles or processes which the human body uses in order to produce
ATP from catabolizing each molecule of glucose are;
1. Glycolysis
2. Krebs cycle/ citric acid cycle/ tricarboxylic acid cycle(TCA)
3. Beta- oxidation (Bolte, Rensing & Maier, 2015).
Describe in great detail the “raw products” that go into each cycle as well as the
“end product” that comes out of each process
1. Glycolysis:
Steps of glycolysis:
Step1: conversion of D-glucose (raw material) to glucose-6-phosphate, catalysed by
hexokinase.
Step2: Phosphoglucose Isomerase rearranges glucose 6-phosphate (G6P) into fructose 6-
phosphate (F6P)
Step3: Fructose 1,6-bisphosphate in obtained from fructose 6-phosphate by
Phosphofructokinase consisting of magnesium as its cofactor.
Step4: Fructose 1,6-bisphosphate is divided into two molecules of sugars; dihydroxyacetone
phosphate(DHAP) and glyceraldehyde 3-phosphate (GAP) by the enzyme Aldolase.
Step5: the two sugar molecules DHAP and GAP is interchanged by Triophosphate isomerase
and a molecules of glyceraldehyde phosphate is detached and used in the further step of the
glycolysis process.

2EXERCISE SCIENCE
Step6: the glyceraldehyde 3-phosphate (GAP) get dehydrogenated to 1,3-
bisphosphoglycerate by glyceraldehyde 3-phosphate dehydrogenase (GAPDH).
Step7: a phosphate group is transferred from 1,3-bisphosphoglycerate to a molecule of ADP
to convert to 3-phosphoglycerate and ATP by phosphoglycerate kinase.
Step8: the phosphate group from the 3rd carbon atom is relocated by the phosphoglyverol
mutase from 3-phosphoglycerate to the 2nd carbon atom to develop 2-phosphoglycerate.
Step9: from 2-phosphoglycerate, a molecule of water is removed by enolase to form
phosphoenol pyruvic acid (PEP)
Step10: ADP receives a phosphate molecule from PEP by pyruvate kinase to form pyruvic
acid and ATP (end product) (Li, Gu & Zhou, 2015).
2. Krebs cycle/ citric acid cycle/ tricarboxylic acid cycle(TCA):
Step1: a molecule of two carbon called acetyl CoA (raw material) combines to a four
carbon molecule, oxaloacetate to convert into a 6 carbon molecule called citrate.
Step2: isocitarte is converted from the molecule of citrate.
Step3: alpha-ketoglutarate is formed by the oxidisation of isocitrate releasing carbon dioxide
with formation of a molecule of NADH.
Step4: succinyl CoA is formed by the oxidisation of alpha-ketoglutarate with the acceptance
of coenzyme A and forming a molecule of NADH.
Step5: production of one GTP molecule along with the conversion of succinate from succinyl
CoA.
Step6: production of FADH₂ along with conversion of fumarate from succinate.
Step7: malate is converted from fumarate.

3EXERCISE SCIENCE
Step8: NADH is produced while the conversion of oxaloacetate from malate (end product)
(O’Neill, 2015).
3. Beta-oxidation:
Step1: removal of 2 hydrogen bonds in between 2nd and 3rd carbon atoms by dehydrogenation
which is catalysed by the enzyme Acyl-CoA dehydrogenase.
Step2: enoyl-CoA hydratase catalyses hydration adding water molecule across double bonds
Step3: 3-hydroxyacyl-CoA dehydrogenase catalyses dehydrogenation generating NADH
Step4: beta-ketothiolase catalyses thiolytic cleavage, cleaving the Acetyl-CoA molecule at
the terminal forming a new molecule of Acyl-CoA. The molecule is 2 carbons deficient of the
previous molecule.
Acetyl-CoA which is generated during the beta-oxidation pathway then enters the
TCA cycle, later oxidized in order to produce NADH and FADH, used in electron transport
chain to generate ATP (Bolte, Rensing & Maier, 2015).
Discuss why it may be better to utilize free fatty acids as a raw source of fuel versus
carbohydrates.
It is better to use free fatty acids as a raw energy source then carbohydrate as the
energy content of fat is 9.3 kcal/g and the carbohydrate has energy content of 4.3 kcal/g
which states that fat has the higher efficiency to provide energy to the body then carbohydrate
(Maditz et al., 2015).

4EXERCISE SCIENCE
Why it is the body’s preference not to use protein as a source of fuel unless it has to
do so?
It is preferred by the body not to use protein as protein source as it is present is its
tertiary structure which is difficult to break and also it has energy content of 4.2 kcal/g (Jiang
et al., 2016).

5EXERCISE SCIENCE
Reference:
Bolte, K., Rensing, S. A., & Maier, U. G. (2015). The evolution of eukaryotic cells from the
perspective of peroxisomes: phylogenetic analyses of peroxisomal beta‐oxidation
enzymes support mitochondria‐first models of eukaryotic cell evolution. BioEssays,
37(2), 195-203.
Jiang, S., Wu, X., Luo, Y., Wu, M., Lu, S., Jin, Z., & Yao, W. (2016). Optimal dietary
protein level and protein to energy ratio for hybrid grouper (Epinephelus
fuscoguttatus♀× Epinephelus lanceolatus♂) juveniles. Aquaculture, 465, 28-36.
Li, X. B., Gu, J. D., & Zhou, Q. H. (2015). Review of aerobic glycolysis and its key
enzymes–new targets for lung cancer therapy. Thoracic cancer, 6(1), 17-24.
Maditz, K. H., Smith, B. J., Miller, M., Oldaker, C., & Tou, J. C. (2015). Feeding soy protein
isolate and oils rich in omega-3 polyunsaturated fatty acids affected mineral balance,
but not bone in a rat model of autosomal recessive polycystic kidney disease. BMC
nephrology, 16(1), 13.
O’Neill, L. A. (2015). A broken krebs cycle in macrophages. Immunity, 42(3), 393-394.