20. Which ofthe following is not an intermediate in the C4 pathway?
(A) Malate.
(B) Pyruvate.
(C) Phosphoenolpyruvate.
(D) Fumarate.
(E) Oxaloacetate.

21. Which one of the following statements is incorrect? (A) Rafts are enriched in sphingolipids and cholesterols. (B) A region with more than 20 residues of high hydropathy index is presumed to be a transmembrane segment. (C) The positively charged Lys, His, and Arg residues of membrane proteins occur more commonly on the cytoplasmic face of membranes. (D) Glycosyl phosphatidylinositol (GPI)-linked proteins are always on the inner face of the plasma membrane. (E) Lamin A uses the farnesyl group to anchor at the nuclear inner membrane. Unable to cleave pre-Lamin A/C from the nuclear inner membrane may cause premature aging.

22. Which one of the following statements is incorrect? (A) A transporter can significantly reduce the for polar compounds and ions across the membrane bilayer. (B) P-type ATPases are sensitive to the phosphate analog vanadate. (C) ATPase, an antiporter for outward 2 Na ions and inward ions, produces the membrane potential of-50 to -70 mV. (D) The multidrug transporter (MDR1), an ABC transporter, is responsible for the drug resistance in certain tumors. (E) Cystic fibrosis is resulted from a defective chloride ion channel.

23. Which one of the following statements is incorrect? (A) Epinephrine and glucagon activate adenylyl cyclase to free fatty acids from adipocytes. (B) Defective perilipin cannot promote hormone-sensitive lipase-mediated adipocyte lipolysis. (C) The fatty acids with acyl chain lengths of 12 or fewer carbons enter mitochondria without the help of membrane transporters. (D) Fatty acids with 14 or more carbons must be through the carnitine shuttle to enter the mitochondrial membranes. (E) Coenzyme A in the mitochondrial matrix is largely used in the biosynthesis of fatty acids; whereas cytosolic coenzyme A is used in oxidative degradation of fatty acids.

24. Which one of the following statements is incorrect? (A) Malonyl-CoA negatively regulates carnitine acyltransferase I. (B) During vigorous exercise, glucagon activates protein kinase A (PKA) to phosphorylate acetyl-CoA carboxylase and reduce malonyl-CoA synthesis. (C) The peroxisomal ẞ oxidation is active on very-long-chain fatty acids. (D) Branched fatty acids with methyl groups, such as phytanic acid (16 C), are catabolized in peroxisomes by a oxidation. (E) In vertebrates, the preferred substrates for oxidation are fatty acids of 20 to 26 carbon atoms.

25. Which one of the following statements is incorrect? (A) All cells can synthesize cholesterol from acetyl-CoA. (B) The B-hydroxy-B-methylglutaryl-CoA (HMG-CoA) synthase for cholesterol synthesis is simultaneously responsible for the ketone body formation in the mitochondria. (C) The reduction of HMG-CoA to mevalonate by HMG-CoA reductase is a rate-limiting step, which can be inhibited by statins. (D) Adrenal gland and gonads use cholesterol as a precursor for steroid hormones. (E) Cholesterol and cholesteryl esters are carried in the blood plasma as lipoproteins.

26. Which one of the following statements is incorrect? (A) Humans have the enzyme to synthesize the o-3 a-linolenic acid (ALA; 18:3. (B) Fish oils are rich in eicosapentaenoic acid (EPA; 20:5 and docosahexaenoic acid (DHA; 22:6. (C) The "Mediterranean diets" contain rich -3 polyunsaturated fatty acids (PUFAs). (D) In all naturally unsaturated fatty acids, the double bonds are in the cis configuration. (E) Intake of more trans fatty acids leads to a higher incidence of cardiovascular disease.

27. Which of the following statements is false in reference to the mammalian synthesis of urea? (A) The carbon atom of urea is derived from mitochondrial . (B) Aspartate directly donates a nitrogen atom for the formation of urea during the urea cycle. (C) The activity of urea cycle is regulated by the rates of synthesis of the four urea cycle enzymes and carbamoyl phosphate synthetase I. (D) Arginine is an inhibitor of the urea cycle. (E) The process of urea production is an energy-consuming series of reactions.

28. Which of the following statements concerning the nitrogen excretion and the urea cycle in mammals is false? (A) The reaction of the combination of ammonia with glutamate to form glutamine requires ATP. y-Glutamyl phosphate is an intermediate in the reaction. (B) Glutamate is metabolically converted to a-ketoglutarate and by a process described as oxidative deamination. (C) generated in liver mitochondria is immediately used, together with CO2 (as ), to form carbamoyl phosphate. This reaction is catalyzed by carbamoyl phosphate synthetase I and requires ATP. (D) The urea cycle causes a net conversion of oxaloacetate to malate. (E) The pathways of the citric acid cycles and the urea cycles are interconnected, and the pathway interconnections decrease the energetic cost of urea synthesis.

29. Which of the following conversions require more than one step? 1. Alanine → pyruvate 2. Phenylalanine → hydroxyphenylpyruvate  3. Aspartate → oxaloacetate 4. Glutamate → ketoglutarate 5. Proline → glutamate (A) 2 and З. (B) 1, 2, and 4. (C) 1, 3, and 5. (D) 2 and 5. (E) 2, 3, and 5.

30. Which of the following descriptions is false? (A) The conversion of glutamate to an a-keto acid and NH4 is accompanied by ATP hydrolysis. (B) Most amino acids are metabolized in the liver; however, the three amino acids with branched side chains (leucine, isoleucine, and valine) are oxidized as fuels primarily in muscle, adipose, kidney, and brain. (C) In liver mitochondria, glutaminase catalyzes the reaction to release the amino group from glutamine; the products are glutamate and ammonia. (D) Genetic defects in the urea cycle can not be treated by a protein-free diet. (E) Alanine can play the role to transport ammonia from skeletal muscles to the liver. In muscles, glutamate can transfer its a-amino group to pyruvate to form alanine by alanine aminotransferase.

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