Rat heart muscle operating aerobically fills more than 90% of its ATP needs by o
ID: 67298 • Letter: R
Question
Rat heart muscle operating aerobically fills more than 90% of its ATP needs by oxidative phosphorylation. Each gram of tissue consumes Oxygen at the rate of 10.0 micromol/min, with glucose as the fuel source.
(a) Calculate the rate at which the heart muscle consumes glucose and produces ATP.
(b) Consider an alternate scenario – what would be the rate of consumption if the energy source were triglycerides whose fatty acyl chains were each 12-C in length and saturated. (assume the same rate of 10.0 micromol/min of oxygen consumption).
(c) For a steady-state concentration of ATP of 5.0 micromol/g of heart muscle tissue, calculate the time required (in seconds) to completely turn over the cellular pool of ATP. What does this result indicate about the need for tight regulation of ATP production? (Note: Concentrations are expressed as micromoles per gram of muscle tissue because the tissue is mostly water.)
Explanation / Answer
(a)
Glucose oxidation requires 6 mol of oxygen per mol of glucose. Therefore, glucose is consumed at the rate of 10 / 6 = 1.7 micro mol / minute gram of tissue. If each glucose produces 32 ATP, the muscle produces ATP at the rate of about 1.7 x 32 = 54.4 micro mol / minute gram of tissue or 0.91 micro mol / sec / gram.
(b)
The overall equation for beta oxidation of 12 carbon saturated fatty acid is as follows:
CH3- (CH2)10 - COSCoA + 5 NAD+ + 5 FAD + 5 CoASH + 5 H2O = 6 CH3 - COSCoA + 5 NADH + 5 FADH2 + 5H+
The breakdown by an organism of 1 mol of 12 carbon saturated fatty acid requires 1 mol of ATP (for activation) and forms 6 mol of acetyl-CoA.
1 mol of ATP is split to AMP and 2Pi = 2 ATP
6 mol of acetyl-CoA formed (6 × 12) = 72 ATP
5 mol of FADH2 formed (5 × 2) =10 ATP
5 mol of NADH formed (5 × 3) = 15 ATP
Total = 99 ATP
The combustion of 1 mol of 12 carbon fatty acid
C12H32O2 + 19 O2 = 12 CO2 + 16 H2O + energy
Therefore, glucose is consumed at the rate of 10 / 19 = 0.52 micro mol / minute gram of tissue. If each 12 carbon saturated fatty acid produces 99 ATP, the muscle produces ATP at the rate of about 0.52 x 99 = 51.48 micro mol / minute gram of tissue or 0.86 micro mol / sec / gram.
(c)
It will take about 5.5 seconds to produce ATP at a level of 5 micro mol / gram. This indicates that the entire pool of ATP in muscle must be regenerated every 5.5 seconds. In order to do this, the cell must regulate ATP synthesis very precisely.
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