Thought Questions 1. Breakdown of fats generates acetyl CoA, which is subsequent

Question

Thought Questions 1. Breakdown of fats generates acetyl CoA, which is subsequently oxidized in the citric acid cycle. a. How many ATP/GTP can be generated from one molecule of acetyl CoA? b. Does this ATP/GTP generation require oxygen? Can a sprinter utilize fats as a significant source of energy while sprinting? Explain. c. 2. The following graph plots the length of time exercise could be maintained at moderately high intensity as a function of initial muscle glycogen levels (as a side note, note that the different levels of muscle glycogen were established by different levels of "carboloading" prior to exercise). Why might initial muscle glycogen levels be so highly correlated with endurance at a moderately high level of exercise? 400 Diets O High CHO O Mixed Low CHO. 300 R-0.93 100 p 0.00001 Endurance time at 75% VO2max (hours) 3.9 The linear relationship between preexercise muscle glycogen concentrations and -se duration at 75% VO.max. tom data in Hermansen, Hultman, et al. (1967)

Explanation / Answer

1a. ANS: One molecule of acetyl-CoA is degraded through citric acid cycle or TCA cycle produces 3 molecules of NADH at step 4, 5 and 9 (one in each of the enzymatic reaction catalyzed by isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase and malate dehydrogenase respectively) and 1 molecule of GTP at step 6 by succinyl-CoA synthetase and 1 molecule of FADH at step 7 by succinate dehydrogenase

One turn of Citric Acid Cycle completely degraded Acetyl Co A into CO2 and H2O and produces 3 NADH, 1 FADH2an d 1GTP.

3 NADH = 3 x 3 = 9 ATP

1 FADH2 =1 x 2 = 2 ATP

1 GTP =                  1 ATP

Total no. Of ATPs = 12 ATP

1b. ANS: During the citric acid cycle the NADH and FADH2 produced transfer their electrons to the next pathway in the system, which will use oxygen so it is considered an aerobic pathway. But in the citric acid cycle very little amount of ATP was directly produced and it does not directly consume oxygen.

1c. ANS:

The primary source of energy during low-to-moderate aerobic exercise is fat, which accounts for approximately 60 percent of the calories burned during activity, according to the American Council on Exercise. Your body will burn circulating fat from food before tapping into stored fat. Carbohydrates convert to glycogen to provide the remainder of the fuel used for moderate exercise. If glycogen is not available, your body may use protein for fuel, but this is more likely during higher intensity exercise.

When we perform exercise, we trigger the breakdown of these triglycerides in the muscle fibre and adipose tissue. Exercise stimulates the release of lipase and epinephrine, both of which cause lipolysis that results into formation of three molecules of free fatty acids acids (FFA) and glycerin, which now becomes available for any concurrent activity. That is the reason why fat is used as fuel when person is exercising at VO2max.

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