9. Compare the energy cost, in ATP equivalents, of synthesizing stearate from mitochondrial acetyl-CoA to the energy recovered by degrading stearate to CO2. assume NADH (or NADPH) and FADH2 yield 2.5 and 1.5 ATP equivalents, respectively. Remember that FAS stops at palmitate; the pathway for further elongation is shown in the book (Fig. 20-28). Don’t forget steps needed to generate malonyl-CoA or transport of acetyl-CoA out of the mitochondria.
9.
Compare the energy cost, in ATP equivalents, of synthesizing
stearate from mitochondrial acetyl-CoA to the energy recovered by
degrading stearate to CO2.
assume NADH (or NADPH) and FADH2 yield 2.5 and 1.5
ATP equivalents, respectively. Remember that FAS stops at palmitate; the pathway for
further elongation is shown in the book (Fig. 20-28). Don’t forget steps needed to
generate malonyl-CoA or transport of acetyl-CoA out of the mitochondria.
Please show me detailed solution.
Stearate is a 18 carbon saturated fatty acid. Lets first look at the amount of ATP equivalents required for Stearate biosynthesis.
First 16 Carbon long , saturated fatty acid called palmitate is synthesized in the cytoplasm. For this 8 Acetyl Co.A molecules are first transported from the mitochondrial matrix to cytoplasm. The transport mechanism involving citrate, oxaloacetate, malate and pyruvate is used. It is a cyclic process where acetyl Co.A is combined with oxaloacetate to form citrate in the mitochondrial matrix and then transported into cytoplasm. In cytoplasm reverse reaction takes place to yield oxaloacetate and acetyl Co.A. Acetyl Co.A is taken for palmitate synthesis while OAA has to be transported back to matrix and converted to oxaloacetate so that it can bind with another molecule of acetyl Co.A and transport it to cytoplasm. As you can see this transport process is cyclic. For the transport of 1 acetyl Co. A from mitochondrial matrix to cytoplasm and regeneration of oxaloacetate, 2 ATP is required.
8 acetyl Co.A is required to synthesize palmitate in cytoplasm. Hence the transport of 8 acetyl Co.A from mitochondrial matrix to cytoplasm require 16 ATP.
7 cycles () of a reaction mechanism done by the enzyme complex Fatty Acid Synthase (FAS) is required to form 16 carbon palmitate. For this 7 malonyl Co. A and 1 acetyl Co.A are required. 7 out of the 8 acetyl Co.A with us is converted to malonyl Co.A . This requires 1 ATP per conversion of acetyl Co. A to malonyl Co.A. So a total of 7 ATP is required.
Each cycle or reaction conducted by FAS requires 2 NADPH. Hence 7 cycles requires 14 NADPH.
Trending now
This is a popular solution!
Step by step
Solved in 3 steps
