Explain how enzymes are involved in processes such as the breakdown of fructose.

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Enzymes are integral to processes such as the breakdown of fructose, a monosaccharide. Thus, a deficiency in enzymes can cause malabsorption of fructose or other sugars. Chemically, enzymes are complex proteins. Some enzymes like fructokinase transform molecules into available energy via processes of metabolism. For example, fructokinase and aldolase B. are enzymes involved in the breakdown of fructose. Any imbalance or absence of these and other enzymes can lead to fructose intolerance in the person, leading to a number of medical symptoms. When fructose cannot be metabolized by enzymes, it may lead to reduced absorption of water in the intestines, which in turn may lead to “bloating, diarrhoea or constipation, flatulence, and stomach pain due to muscle spasms. (Breakspear Medical Group, n.d.).

Found throughout the human body, enzymes can be considered to be chemical catalysts that convert substances like fructose into energy that is necessary and available to the system. The method by which enzymes work includes their actually changing shape, or creating what can be called welcoming sites. Shape changes or welcoming sites on their own molecules allow the enzyme molecules like those of fructokinase to welcome other molecules, like those in fructose. However, sometimes enzymes can become less powerful or denatured; they cannot therefore breakdown substances like fructose.

B1. Explain what would happen to the amount of energy available to a cell if the entire Cori cycle occurred and remained within that single cell (i.e., a muscle cell).

The mitochondria are the primary locus of energy generation within cells. Effective functioning of mitochondria is critical for the maintenance of life and health. When any aspect of cellular metabolism is compromised in the mitochondria, the result can be deadly. The Cori cycle is a metabolic process involving both the body’s muscles and one of its most critical organs, the liver.

If the Cori cycle occurred and remained within a single cell, such as a muscle cell, that amount of energy would stagnate and never be transferred to the liver and back to the muscles. Thus, the body would be adversely deprived of energy. This would explain the patient’s motor weakness, inability to stand for long periods of time, and general fatigue. A thorough and comprehensive Cori cycle is necessary for the optimal functioning of the human body. Typically, the Cori cycle involves anaerobic glycolysis and lactate releasing into the bloodstream and subsequently the liver. A person with mitochondrial disease may experience elevated lactic acid levels in the blood due to an inefficient or ineffective Cori cycle (United Mitochondrial Disease Foundation, n.d.).

B2. Explain where in the citric acid cycle a hypothetical defect of an enzyme could occur that prevents an increase in adenosine triphosphate (ATP) production in response to an increased energy need and how the products of the citric acid cycle are converted into ATP.

If an enzyme is defective in the sense that it prevents an increase in adenosine triphosphate (ATP) in spite of there being an increased need for energy in the body, then it would account for symptoms like muscular weakness and fatigue. The citric acid cycle is one of the most important metabolic cycles in the human body. During the citric acid cycle, most of the adenosine triphosphate (ATP) needed for energy is produced (“Citric Acid Cycle Summary”). Converting products of the citric acid cycle, such as carbon compounds and fatty acids, into ATP, involves a complex process of metabolism. Also known as the Krebs cycle, the citric acid cycle is the most fundamental of food-related metabolism. All inputs to the body such as fats, protein, and carbohydrates, can be converted into ATP in the cells via electron transport. Oxidation is the cornerstone of the process by which the products of the citric acid cycle are converted into ATP. The point in the citric acid cycle in which a hypothetical defect of an enzyme, like those that cause mitochondrial disease, occurs would be glycogenesis.


Breakspear Medical Group (n.d.). Fructose metabolism — acumen. Retrieved online:

“Citric Acid Cycle Summary.” Retrieved online:

“Glycolysis, Krebs Cycle, and other Energy-Releasing Pathways,” (n.d.). Retrieved online:

United Mitochondrial Disease Foundation (n.d.). What is mitochondrial disease? Retrieved online: