CellularMetabolism

CellularMetabolism - Chapter 2 Cellular Metabolism Tommy...

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Chapter 2 Cellular Metabolism Tommy Boone, PhD, MPH, FASEP, EPC and Larry Birnbaum, PhD, MA, EPC Energy is necessary for muscle contraction, which is critical for human movement. Chemical substances such as carbohydrates, lipids, and proteins provide the energy for movement by muscle contraction. The nutrients yield usable forms of energy (a process called catabolism) from the chemical activities (i.e., metabolism) that take place in the muscle fibers. Since the body’s metabolism is increased with exercise, the oxidation or breakdown of the nutrients is increased to provide more energy in the form of adenosine triphosphate, ATP. The catabolism of glucose by way of glycolysis and the Krebs cycle supplies the electrons that produce energy within the electron transport chain . Fats can also be converted to compounds that are intermediate products in the catabolism of glucose. Depending upon the work that is required of the fiber, not all the glucose undergoes glycolysis. Some is combined with other glucose molecules to form glycogen (this process is called glycogenesis ). When there is an increased need for glucose as a source for energy, the stored glycogen is broken down into glucose to undergo glycolysis. This process of converting glycogen into glucose is called glycogenolysis . The purpose of bioenergetics (i.e., the conversion of foodstuffs into usable energy-rich phosphate compounds, ATP) is to insure cellular energy production. In regards to exercise, the energy within the ATP molecule is used for muscle contraction. The compound itself is a combination of a molecule of adenine and ribose (referred to as adenosine) linked to three phosphates. The bonds of the two outer phosphates represent potential energy. When the enzyme ATPase breaks these bonds, energy is released to do work. Indeed, the hydrolysis of ATP to adenosine diphosphate (ADP), inorganic phosphate (P i ), and energy is critical to the sliding of filaments, known as myofibrils, and muscle contraction (see the Skeletal Muscle chapter). Because ATP is the universal energy donor for cellular work, cells must be able to produce it. Fortunately, there are several pathways to insure a constant supply. The most immediate is the ATP-PC system . PC stands for phosphocreatine, which is also written as creatine phosphate (CrP). PC hydrolysis regenerates ATP by giving its phosphate to ADP to form ATP (figure 1). The enzyme creatine kinase (CK) is involved in the donation of phosphate to ADP. This process does not require oxygen. It is entirely anaerobic. All forms of intense exercise, such as sprinting, weight lifting, and gymnastics, are possible because of the phosphagen system. Another metabolic pathway that produces ATP is glycolysis . It is an anaerobic pathway that ends with the breakdown of glucose into two, 3-carbon molecules of lactic acid. The third pathway is defined as
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aerobic ATP production. It involves glycolysis, the Krebs cycle , and the electron transport chain . Oxygen is not used in the Krebs cycle, but it is the final electron acceptor of the electron transport chain.
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CellularMetabolism - Chapter 2 Cellular Metabolism Tommy...

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