BCH 4054 HOUR TEST 2 NAME _____________________ October 20, 1995 (18) 1. Calculate the number of ATP's that can be obtained from the complete oxidation of one mole of pentanoic acid (CH3CH2CH2CH2COOH) to CO2 and water. Sketch the overall pathway, showing names or structures of intermediates, and indicating where ATP's would be used or produced (including ATP production by the reoxidation of NADH and CoQH2). Start with pentanoic acid that has just entered the cell across the plasma membrane. (Note: This is an odd-chain fatty acid). 2. The thioester of a á-ketoacid is an intermediate in both fatty acid oxidation and fatty acid synthesis. Compare and contrast the catabolic and anabolic pathways for fatty acids by giving the following information about the á-ketoacid intermediate for each pathway. (2) (a) The identity of the thiol group involved in the thioester in each case. (6) (b) The reaction forming the á-ketothioester in each pathway. Give structures of reactants and products (nucleotides and prosthetic groups may be abbreviated). (6) (c) The reaction utilizing the á-ketothioester in each pathway. Give the structures of reactants and products (nucleotides and prosthetic groups may be abbreviated). (6) 3. Leucine and lysine are ketogenic amino acids, while alanine and aspartate are glucogenic. What common feature in the degradation of each pair leads to this classification? (It is not the first initial). Answer question 4 or 5 (8) 4. Explain the role of carnitine in fatty acid oxidation. (8) 5. Explain the role of citrate in fatty acid synthesis. (8) 6. CTP is required for the activation of metabolic intermediates in phosphoglyceride biosynthesis. Give the structure of the active intermediate, and the name or structure of the compound it reacts with, in the formation of the following phosphoglycerides in animal tissues: (a) phosphatidyl choline (b) phosphatidyl inositol Answer question 7 or 8. (8) 7. Give the reactions catalyzed by the enzymes ACAT and LCAT, and the location of each enzyme in the body. (8) 8. The hydrolysis of phosphatidyl inositol diphosphate by phospholipase A2 and by phospholipase C are important reactions in hormonal regulation that produce several second messengers. Identify the products formed when each of these enzymes acts on phosphatidyl inositol diphosphate. (a) phospholipase A2 (b) phospholipase C (12) 9. For the four plasma lipoproteins, (a) chylomicrons, (b) VLDL, (c) LDL, and (d) HDL, put the letter or letters corresponding to the lipoprotein(s) for which the following statements are true in the blank to the left of the statement: ________ Contains apoprotein B-100. ________ Contains apoprotein B-48. ________ Contains apoprotein A-1. ________ Contains apoprotein C-1. ________ Source of cholesterol for tissues. ________ Transports dietary triacylglycerols. ________ Transports endogenous (made in liver) triacylglycerols. ________ Is degraded by lipoprotein lipase. ________ Is taken up by cells via receptor-mediated mechanisms. ________ Is a precursor of LDL. ________ May remove cholesterol from cells. ________ Is acted on by the enzyme LCAT. (12) 10. Identify the cellular location of each of the five urea cycle enzymes listed below as either the cytosol (C) or mitochondria (M). ____ Carbamoyl phosphate synthetase I ____ Ornithine transcarbamoylase ____ Argininosuccinate synthetase ____ Argininosuccinate lyase ____ Arginase Which urea cycle intermediates must be transported across the mitochondrial membrane? Fumarate is formed in which reaction? Aspartate is used in which reaction? How is fumarate converted back to aspartate? (Show the pathway). 11. Glutamine synthetase is regulated in bacteria both by allosteric end- product inhibition and by covalent modification. (2) (a) What type of covalent modification is involved? (2) (b) Is the modified enzyme the active or inactive form? (4) (c) The state of the enzyme (modified or unmodified) depends on the concentrations of glutamine and of alpha-ketoglutarate. Explain how these compounds regulate the modification of the enzyme. (4) 12. Tetrahydrofolic acid (THFA) exists in several derivative forms: (a) N10-formyl-THFA (b) N5-N10-methylene-THFA (c) N5-N10-methenyl-THFA (d) N5-methyl-THFA Which of these forms (identify by putting the correct letter or letters in the blank) ____ is formed in the degradation of serine? ____ furnishes the methyl group in methionine biosynthesis? ____ contains a C-1 group at the oxidation level of methanol? ____ contains a C-1 group at the oxidation level of formaldehyde? (2) 13. Gaucher's disease is a sphingolipid storage disease marked by the accumulation of the sphingolipid glucosyl-ceramide (also known as glucocerebroside). What is the metabolic defect in this disease?