From the list of terms provided below, fill in the blanks appropriately such tha
ID: 58354 • Letter: F
Question
From the list of terms provided below, fill in the blanks appropriately such that the text passages, when complete, correctly describe the production of energy (i.e. of ATP) in skeletal muscle cells at rest as compared to during exercise.
Terms: aerobic, anaerobic, beta oxidation, Cori cycle, decreased, fats, fatty acid, increased, lactic acid, sugars
At rest, skeletal muscle cells derive more than half (roughly 60%) of the ATP needed to meet their energy requirements by burning ______. Specifically, using the process of ___________, they break down the ____________ components of triglyceride type lipids to generate acetyl CoA and reduced NADH and FADH2. These products are then metabolized under _____________ conditions, using Kreb's cycle and the electron transport chain in the mitochondria to generate large amounts of ATP in the presence of oxygen. The remainder of the cells' energy needs are met predominantly by burning ______________, primarily glucose. If oxygen is readily available, like the fatty acids, glucose can be metabolized aerobically using glycoysis, Kreb's cycle and the activity of the electron transport chain.
However, when one engages in exercise - skeletal muscle must 'tweak' its fuel mixture and begin metabolizing ____________ amounts of glucose. The reason for this change is because glycolysis of glucose, while it generates only small amounts of ATP per cycle - does this really quickly which is beneficial to the muscle during exercise. When the glucose and fat can be metabolized in the presence of oxygen, the NADH produced by glycolysis can also boost ATP production in the skeletal muscle cells. However, if exercise is prolonged and/or of increasing intensity, there can be periods where oxygen availability in the tissues is ___________ to the point it becomes transiently unavailable, forcing the skeletal muscle cells to burn their fuels under ____________ conditions. At these times, fats cannot be used for ATP production because, in the absence of oxygen, the metabolic processes used to burn fats (i.e. Kreb's cycle and the ETC) cannot operate. When the muscle is working under these anaerobic conditions, only glucose metabolism via glycolysis can provide for ATP production to the skeletal muscle cells. When glycolysis occurs in the absence of oxgyen, the pyruvate generated gets converted to ______________, which like other acids, is caustic and causes localized irritation/damage to skeletal muscle cells as it accumulates. So when you are exercising to the point you 'feel the burn' you are feeling the soreness that occurs in response to tissue damage induced by acid accumulation in your muscles while your muscle cells are 'burning' their sugar without oxygen. Another major metabolic pathway that becomes active during anaerobic periods is ______________, the metabolic pathway designed to minimize the accumulation of the lactic acid in tissues. In this pathway, lactic acid diffuses out of the cell and into blood, which carries the organic acid to the liver. The liver takes up the lactic acid and utilizes it as a substrate for glucose production by gluconeogenesis. The liver-derived glucose then diffuses back into blood and returns to skeletal muscle, where the cells take it up and anaerobically metabolize it via glycolysis until aerobic metabolism resumes.
Explanation / Answer
At rest, skeletal muscle cells derive more than half (roughly 60%) of the ATP needed to meet their energy requirements by burning carbohydrates fatty acids or lipids. Specifically, using the process of beta-oxidation, they break down the fatty acids components of triglyceride type lipids to generate acetyl CoA and reduced NADH and FADH2. These products are then metabolized under aerobic conditions, using Kreb's cycle and the electron transport chain in the mitochondria to generate large amounts of ATP in the presence of oxygen. The remainder of the cells' energy needs are met predominantly by burning carbohydrates primarily glucose. If oxygen is readily available, like the fatty acids, glucose can be metabolized aerobically using glycolysis, Kreb's cycle and the activity of the electron transport chain.
However, when one engages in exercise - skeletal muscle must 'tweak' its fuel mixture and begin metabolizing small amounts of glucose. The reason for this change is because glycolysis of glucose, while it generates only small amounts of ATP per cycle - does this really quickly which is beneficial to the muscle during exercise. When the glucose and fat can be metabolized in the presence of oxygen, the NADH produced by glycolysis can also boost ATP production in the skeletal muscle cells. However, if exercise is prolonged and/or of increasing intensity, there can be periods where oxygen availability in the tissues is reduced to the point it becomes transiently unavailable, forcing the skeletal muscle cells to burn their fuels under anaerobic conditions. At these times, fats cannot be used for ATP production because, in the absence of oxygen, the metabolic processes used to burn fats (i.e. Kreb's cycle and the ETC) cannot operate. When the muscle is working under these anaerobic conditions, only glucose metabolism via glycolysis can provide for ATP production to the skeletal muscle cells. When glycolysis occurs in the absence of oxgyen, the pyruvate generated gets converted to lactate, which like other acids, is caustic and causes localized irritation/damage to skeletal muscle cells as it accumulates. So when you are exercising to the point you 'feel the burn' you are feeling the soreness that occurs in response to tissue damage induced by acid accumulation in your muscles while your muscle cells are 'burning' their sugar without oxygen. Another major metabolic pathway that becomes active during anaerobic periods is cori-coir cycle, the metabolic pathway designed to minimize the accumulation of the lactic acid in tissues. In this pathway, lactic acid diffuses out of the cell and into blood, which carries the organic acid to the liver. The liver takes up the lactic acid and utilizes it as a substrate for glucose production by gluconeogenesis. The liver-derived glucose then diffuses back into blood and returns to skeletal muscle, where the cells take it up and anaerobically metabolize it via glycolysis until aerobic metabolism resumes.
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