1. Which of the following statements about the fixation of atmospheric nitrogen (N2) into NH3 by living cells is false?
A) It involves the transfer of
... [Show More] eight electrons per mol of N2.
B) It occurs in certain microorganisms, but not in humans.
C) It requires a source of electrons, normally ferredoxin.
D) It requires one ATP per mol of N2 fixed.
E) It requires two key protein components, each containing iron.
D
2. Which of the following is not true about the anammox reaction?
A) Anammox converts ammonia to nitrogen.
B) Anammox is performed by symbiotic bacteria of leguminous plants.
C) Anammox generates the highly reactive molecule hydrazine that is a component of rocket fuel.
D) Anammox occursw anaerobically.
E) The ultimate electron acceptor in anammox is nitrite.
B
3. Which of the following enzymes is not involved in the assimilation of inorganic nitrogen into an organic molecule?
A) Dinitrogenase reductase
B) Nitrate reductase
C) Nitrite reductase
D) Nitrile reductase
E) Dinitrogenase
D
4. Which of the following enzymes is not involved in the assimilation of inorganic nitrogen into an organic molecule?
A) Arginase
B) Glutamate dehydrogenase
C) Glutamate synthase
D) Glutamine synthetase
E) Dinitrogenase
A
5. The enzymatic machinery to fix atmospheric N2 into NH4+ is:
A) a means of producing ATP when excess N2 is available.
B) composed of two key proteins, each containing iron.
C) relatively stable when exposed to O2.
D) specific to plant cells.
E) unaffected by the supply of electrons.
B
6. Glutamine synthetase converts _____ to _____ whereas glutamate synthase converts ____ to _____.
A) formate; glutamine; ammonia; glutamate
B) asparagine; glutamine; -ketoglutarate; glutamate
C) alpha-ketoglutarate; glutamine; oxaloacetic acid; glutamate
D) alpha-ketoglutarate; glutamine; alpha-ketoglutarate; glutamate
E) glutamate; glutamine; alpha-ketoglutarate; glutamate
E
7. Which of the following is not true about glutamine amidotransferases?
A) These enzymes proceed via a covalent intermediate.
B) Ammonia is released into a channel.
C) Glutamate is a product of the reaction.
D) ATP is needed to activate the glutamine.
E) A Cys at the active site is critical for the activity of these enzymes.
D
8. Nonessential amino acids:
A) are amino acids other than those required for protein synthesis.
B) are not utilized in mammalian proteins.
C) are synthesized by plants and bacteria, but not by humans.
D) can be synthesized in humans as well as in bacteria.
E) may be substituted with other amino acids in proteins.
D
9. An amino acid that does not derive its carbon skeleton, at least in part, from alpha-ketoglutarate is:
A) arginine.
B) glutamate.
C) glutamine.
D) proline.
E) threonine.
E
10. Glutamine, arginine, and proline:
A) do not have a common precursor.
B) may all be derived from a citric acid cycle intermediate.
C) may all be derived from a Cori cycle intermediate.
D) may all be derived from a glycolytic intermediate.
E) may all be derived from a urea cycle intermediate.
B
11. In which group are all the amino acids closely interrelated metabolically?
A) Arginine, hydroxyproline, and histidine
B) Arginine, tyrosine, and glutamate
C) Glycine, valine, glutamine, and aspartate
D) Ornithine, alanine, glycine, and valine
E) Ornithine, proline, arginine, and glutamate
E
12. If glucose labeled with 14C at C-1 were the starting material for amino acid biosynthesis, the product(s) that would be readily formed is (are):
A) serine labeled at the carboxyl carbon.
B) serine labeled at alpha carbon.
C) serine labeled at the R-group carbon.
D) All of the above
E) None of the above
C
13. An amino acid that does not derive its carbon skeleton, at least in part, from oxaloacetate is:
A) aspartate.
B) lysine.
C) methionine.
D) proline.
E) threonine.
D
14. Homoserine is:
A) a precursor of both methionine and threonine.
B) a precursor of serine.
C) derived from homocysteine.
D) derived from serine.
E) derived from threonine.
A
15. If a cell were unable to synthesize or obtain tetrahydrofolic acid (H4 folate), it would probably be deficient in the biosynthesis of:
A) isoleucine.
B) leucine.
C) lysine.
D) methionine.
E) serine.
D
16. The nitrogen atom in the side chain of lysine is derived from which amino acid?
A) Aspartic acid
B) Glutamic acid
C) Glutamine
D) Asparagine
E) Arginine
B
17. The nitrogen atom in the indole ring of tryptophan is derived from which amino acid?
A) Aspartic acid
B) Glutamic acid
C) Glutamine
D) Asparagine
E) Arginine
C
18. Erythrose 4-phosphate is a precursor of:
A) aspartate.
B) cysteine.
C) phenylalanine.
D) serine.
E) threonine.
C
19. An important intermediate in the biosynthetic pathway to aromatic amino acids is:
A) benzoic acid.
B) lactate.
C) orotate.
D) shikimate.
E) alpha-ketoglutarate.
D
20. Which of the following amino acids derives its nitrogen from a purine ring?
A) Histidine
B) Lysine
C) Arginine
D) Glutamine
E) Tryptophan
A
21. The amino acid__________ and is an intermediate in the biosynthesis of _________.
A) histidine; purines
B) glycine; heme
C) serine; heme
D) serine; sphingosine
E) glutamine; glutathione
B
22. Bile pigments are:
A) formed in the degradation of heme.
B) generated by oxidation of sterols.
C) responsible for light reception in the vertebrate eye.
D) secreted from the pancreas
E) the products of purine degradation.
A
23. Glutathione is a(n):
A) enzyme essential in the synthesis of glutamate.
B) isomer of oxidized glutamic acid.
C) methyl-group donor in many biosynthetic pathways.
D) product of glutamate and methionine.
E) tripeptide of glycine, glutamate, and cysteine.
E
24. The plant hormone indole-3-acetate (auxin) is formed from:
A) arginine.
B) histidine.
C) phenylalanine.
D) threonine.
E) tryptophan.
E
25. L-Dopa is an intermediate in the conversion of:
A) phenylalanine to homogentisic acid.
B) phenylalanine to tyrosine.
C) tyrosine to epinephrine.
D) tyrosine to phenylalanine.
E) tyrosine to phenylpyruvate.
C
26. The amino acid that gives rise to the biological messenger NO is:
A) glutamine.
B) arginine.
C) proline.
D) lysine.
E) histidine.
B
27. The hormones epinephrine and norepinephrine are derived biosynthetically from:
A) arginine.
B) histidine.
C) isoleucine.
D) tryptophan.
E) tyrosine.
E
28. One amino acid directly involved in the purine biosynthetic pathway is:
A) alanine.
B) aspartate.
C) glutamate.
D) leucine.
E) tryptophan
B
29. 5-Phosphoribosyl-alpha-pyrophosphate (PRPP) is a synthetic precursor for all of the following except:
A) AMP.
B) arginine.
C) histidine.
D) tryptophan.
E) UMP.
B
30. Glutamine is a nitrogen donor in the synthesis of:
A) CTP.
B) dTTP.
C) inosinic acid (IMP).
D) orotate.
E) UMP.
C
31. De novo purine biosynthesis is distinguished from de novo pyrimidine biosynthesis by:
A) condensation of the completed purine ring with ribose phosphate
B) incorporation of CO2.
C) inhibition by azaserine (a glutamine analog).
D) participation of aspartate.
E) participation of PRPP (phosphoribosyl pyrophosphate).
B
32. The ribosyl phosphate moiety needed for the synthesis of orotidylate, inosinate, and guanylate is provided most directly by:
A) 5-phosphoribosyl 1-pyrophosphate.
B) adenosine 5'-phosphate.
C) guanosine 5'-phosphate.
D) ribose 5-phosphate.
E) ribulose 5-phosphate.
A
33. The synthesis of purine and pyrimidine nucleotides differ in that:
A) ATP is required in the synthesis of purines but not in the synthesis of pyrimidines.
B) purine biosynthesis starts with the formation of PRPP, whereas pyrimidines incorporate the PRPP near the end of the pathway.
C) purine formation requires a THF derivative, whereas pyrimidine formation does not.
D) pyrimidine biosynthesis is tightly regulated in the cell, whereas purine biosynthesis is not.
E) pyrimidines go through many steps, adding a single carbon or nitrogen each time, whereas the basic skeleton for purines is formed by two main precursors.
B
34. Which one of the following statements is true of the biosynthetic pathway for purine nucleotides?
A) CO2 does not participate in any of the steps in this pathway.
B) Deoxyribonucleotides are formed from 5-phosphodeoxyribosyl 1-pyrophosphate.
C) Inosinate is the purine nucleotide that is the precursor of both adenylate and guanylate.
D) Orotic acid is an essential precursor for purine nucleotides.
E) The amino acid valine is one of the precursors contributing to purine nucleotides.
C [Show Less]