Question

very emergence

1. For each 2-carbon increase in the length of a saturated fatty acid chain, how many more additional numbers of ATP can be formed upon complete oxidation to CO₂ and H₂O? Show your calculation. The table can be drawn to show calculation, if necessary. Description of enzymatic reactions is NOT required.                                                                

                                                                                                                                

2. In the fatty acid synthesis, ATP and NADPH are required.

1. Which step requires ATP? Name the enzyme used in this step.                     

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2. Where are the sources of NADPH?                                                                 

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3. Carbamoyl phosphate synthetase I (CPS I) is present in mitochondrial matrix.

1. Glutamate dehydrogenase is also present in the mitochondrial matrix. Suggest an explanation for the significance for its presence in mitochondrial matrix.      

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2. Write the reaction catalyzed by CPS I.                                                            

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3. What is the role of aspartate in urea cycle?                                                       (1 mark)

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Answer 1

1. ATP generation can be summarized for 16 carbon and 18 carbon fatty acid as

	16 carbon	18 carbon
FADH2	7 cycle x 2 = 14 ATP	8 cycle x 2 = 16 ATP
NADH	7 cycle x 3 = 21 ATP	8 cycle x 3 = 24 ATP
Acetyl CoA	8 cycle x 12 = 96 ATP	9 cycle x 12 = 108 ATP
Activation	= -2 ATP	= -2 ATP
NET ATP produced	131-2= 129 ATP	148-2= 146 ATP

thus, addition of each 2 carbon has a difference of 146-129 = 17 ATP generated by additional 1 NADH, 1 FADH2 and 1 acetyl CoA

2. a. During fatty acid biosynthesis the conversion of acetyl CoA to malonyl CoA requires ATP (enzyme acetyl CoA carboxylase)

  b. the sources of NADPH are HMP shunt and malic enzyme, which converts malate to pyruvate.

3. a. carbamoyl phosphate synthase catalyse the synthesis of carbamoyl phosphate from carbon dioxide and ammonia or ammonium ion in mitochondria.  

b. in urea cycle aspartate combine with citrullin to form arginosuccinate by enzyme argino succinate synthase using ATP.