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Biochemistry > Chapter 22 > Flashcards

Chapter 22 Flashcards

1
Q

Which statement about the fixation of atmospheric nitrogen (N2) into NH3 by living cells is FALSE?
A) It involves the transfer of 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.

A

D) It requires one ATP per mol of N2 fixed.

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2
Q

Which statement is NOT true about the anammox reaction?
A) Anammox converts ammonia into 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 occurs anaerobically.
E) The ultimate electron acceptor in anammox is nitrite.

A

B) Anammox is performed by symbiotic bacteria of leguminous plants.

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3
Q 
Which enzyme 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
A

D) nitrile reductase

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4
Q 
Which enzyme 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

A) arginase

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5
Q

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.

A

B) composed of two key proteins, each containing iron.

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6
Q

Glutamine synthetase converts___to___,whereas glutamate synthase converts__to___.
A) formate; glutamine; ammonia; glutamate
B) asparagine; glutamine; alpha-ketoglutarate; glutamate
C) alpha-ketoglutarate; glutamine; oxaloacetic acid; glutamate
D) alpha-ketoglutarate; glutamine; alpha-ketoglutarate; glutamate
E) glutamate; glutamine; alpha-ketoglutarate; glutamate

A

E) glutamate; glutamine; alpha-ketoglutarate; glutamate

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7
Q

Which statement 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.

A

D) ATP is needed to activate the glutamine.

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8
Q

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.

A

D) can be synthesized in humans as well as in bacteria.

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9
Q 
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.
A

E) threonine.

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10
Q

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.

A

B) may all be derived from a citric acid cycle intermediate.

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11
Q

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

A

E) ornithine, proline, arginine, and glutamate

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12
Q

If glucose labeled with 14C at C-1 were the starting material for amino acid biosynthesis, the product that would be readily formed is:
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 answers are correct.
E) None of the answers is correct.

A

C) serine labeled at the R-group carbon.

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13
Q 
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.
A

D) proline.

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14
Q 
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

A) a precursor of both methionine and threonine.

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15
Q 
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.
A

D) methionine.

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16
Q 
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
A

B) glutamic acid

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17
Q 
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
A

C) glutamine

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18
Q 
Erythrose 4-phosphate is a precursor of: 
A) aspartate.
B) cysteine.
C) phenylalanine. 
D) serine.
E) threonine.
A

C) phenylalanine.

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19
Q 
An important intermediate in the biosynthetic pathway to aromatic amino acids is:
A) benzoic acid.
B) lactate.
C) orotate.
D) shikimate.
E) alpha-ketoglutarate.
A

D) shikimate.

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20
Q 
Which amino acid derives its nitrogen from a purine ring? 
A) histidine
B) lysine
C) arginine 
D) glutamine 
E) tryptophan
A

A) histidine

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21
Q 
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
A

B) glycine; heme

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22
Q 
Bile pigments are:
A) formed in the degradation of heme.
B) generated by oxidation of sterols.
C) responsible for a light reception in the vertebrate eye.
D) secreted from the pancreas
E) the products of purine degradation.
A

A) formed in the degradation of heme.

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23
Q

Glutathione is a(n):
A) enzyme essential in the synthesis of glutamate.
B) an 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.

A

E) tripeptide of glycine, glutamate, and cysteine.

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24
Q 
The plant hormone indole-3-acetate (auxin) is formed from: 
A) arginine.
B) histidine.
C) phenylalanine. 
D) threonine.
E) tryptophan.
A

E) tryptophan.

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25
Q 
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.
A

C) tyrosine to epinephrine.

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26
Q 
The amino acid that gives rise to the biological messenger NO is:
A) glutamine.
B) arginine. 
C) proline. 
D) lysine. 
E) histidine.
A

B) arginine.

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27
Q 
The hormones epinephrine and norepinephrine are derived biosynthetically from: 
A) arginine.
B) histidine.
C) isoleucine. 
D) tryptophan. 
E) tyrosine.
A

E) tyrosine.

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28
Q 
One amino acid directly involved in the purine biosynthetic pathway is: 
A) alanine.
B) aspartate. 
C) glutamate. 
D) leucine.
E) tryptophan
A

B) aspartate.

29
Q 
5-Phosphoribosyl--pyrophosphate (PRPP) is NOT a synthetic precursor for:
A) AMP.
B) arginine. 
C) histidine. 
D) tryptophan. 
E) UMP.
A

B) arginine.

30
Q 
Glutamine is a nitrogen donor in the synthesis of:
A) CTP.
B) dTTP.
C) inosinic acid (IMP).
D) orotate.
E) UMP.
A

C) inosinic acid (IMP).

31
Q

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).

A

B) incorporation of CO2.

32
Q 
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

B) adenosine 5’-phosphate.

33
Q

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.

A

B) purine biosynthesis starts with the formation of PRPP, whereas pyrimidines
incorporate the PRPP near the end of the pathway.

34
Q

Which statement 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.

A

C) Inosinate is the purine nucleotide that is the precursor of both adenylate and guanylate.

35
Q 
Orotic aciduria is an inherited metabolic disease in which orotic acid (orotate) accumulates in the tissues, blood, and urine. The metabolic pathway in which the enzyme defect occurs is:
A) epinephrine synthesis.
B) purine breakdown.
C) purine synthesis.
D) pyrimidine breakdown.
E) pyrimidine synthesis.
A

E) pyrimidine synthesis.

36
Q

Precursors for the biosynthesis of the pyrimidine ring system include:
A) carbamoyl phosphate and aspartate.
B) glutamate, NH3, and CO2.
C) glycine and succinyl-CoA.
D) glycine, glutamine, CO2, and aspartate.
E) inosine and aspartate.

A

A) carbamoyl phosphate and aspartate.

37
Q 
The MOST direct precursors of the nitrogens of UMP are:
A) aspartate and carbamoyl phosphate.
B) glutamate and aspartate.
C) glutamate and carbamoyl phosphate.
D) glutamine and aspartate.
E) glutamine and carbamoyl phosphate.
A

A) aspartate and carbamoyl phosphate.

38
Q 
CMP, UMP, and TMP all have \_\_\_\_\_ as a common precursor.
A) adenosine
B) aspartate
C) glutamine
D) inosine
E) S-adenosyl methionine
A

B) aspartate

39
Q

Which statement is NOT true of the reaction catalyzed by ribonucleotide reductase?
A) Glutathione is part of the path of electron transfer.
B) It acts on nucleoside diphosphates.
C) Its mechanism involves the formation of a free radical.
D) There is a separate enzyme for each nucleotide (ADP, CDP, GDP, UDP).
E) Thioredoxin acts as an essential electron carrier.

A

D) There is a separate enzyme for each nucleotide (ADP, CDP, GDP, UDP).

40
Q

Which statement CORRECTLY describes the biosynthetic pathway for purine nucleotides?
A) Purine deoxynucleotides are made by the same path as ribonucleotides, followed by reduction of the ribose moiety.
B) The first enzyme in the path is aspartate transcarbamoylase (ATCase).
C) The nitrogen in the purine base that is bonded to ribose in the nucleotide is derived originally from glycine.
D) The pathway occurs only in plants and bacteria, not in animals.
E) The purine rings are first synthesized, then condensed with ribose phosphate.

A

A) Purine deoxynucleotides are made by the same path as ribonucleotides, followed by reduction of the ribose moiety.

41
Q 
A cell that is unable to synthesize or obtain tetrahydrofolic acid (H4 folate) would probably be deficient in the biosynthesis of:
A) CMP.
B) GMP.
C) orotate.
D) thymidylate (TMP).
E) UMP.
A

D) thymidylate (TMP).

42
Q 
An intermediate of purine degradation in humans is:
A) glutamate.
B) NH4+ 
C) succinate.
D) urea.
E) uric acid.
A

E) uric acid.

43
Q

Which statement is TRUE about gout?
A) Gout is caused by an excessive breakdown of pyrimidine nucleotides.
B) Gout can be treated by the administration of fluorouracil.
C) Gout is particularly prevalent in patients lacking xanthine oxidase.
D) Gout leads to the deposition of sodium urate crystals in the joints.
E) Eating more liver is an effective way to treat the symptoms of gout.

A

D) Gout leads to the deposition of sodium urate crystals in the joints.

44
Q 
Which drug is NOT chemotherapeutic? 
A) Azaserine
B) Allopurinol 
C) Fluorouracil 
D) Methotrexate 
E) Acivicin
A

B) Allopurinol

45
Q 
Which list CORRECTLY arranges nitrogen-containing species from most to least
oxidized?
A) NO3- >NO2- >NH4+ >N2
B) NO3- >NO2- >N2 >NH4+
C) NO2- >NO3- >NH4+ >N2
D) N2 >NO2- >NO3- >NH4+
E) NO2- >NO3- >N2 >NH4+
A

B) NO3- >NO2- >N2 >NH4+

46
Q

Which statement does NOT accurately describe a difference between heme b and the siroheme found in nitrite reductase?
A) Siroheme contains a larger negative charge than heme b.
B) Siroheme contains no vinyl groups, while heme b does.
C) Siroheme contains tetrahedral carbons in the porphyrin ring, while heme b does not.
D) Siroheme contains four propionate groups, while heme b contains two.
E) Siroheme contains Fe2+, while heme b contains Fe3+

A

E) Siroheme contains Fe2+, while heme b contains Fe3+

47
Q 
Which cofactor or functional group within the context of the nitrate reductase electron- transport chain has the HIGHEST reduction potential?
A) cysteine
B) NAD+
C) FAD
D) molybdenum cofactor
E) cyt b557
A

D) molybdenum cofactor

48
Q

Which statement is FALSE regarding ladderanes?
A) Ladderanes are classified as phospholipids.
B) Ladderanes are associated with annamoxosomes.
C) Ladderanes are amphipathic membrane components.
D) Ladderanes have less conformational flexibility than equivalent fatty acids.
E) None of the statements is false.

A

A) Ladderanes are classified as phospholipids.

49
Q

The bacteria A. vinelandii uncouples oxidative phosphorylation during nitrogen fixation for what reason?
A) It increases the temperature so that the enzymes will function at maximum efficiency.
B) It ensures that the citric acid cycle is fully active and providing substrates for nitrogen fixation.
C) It ensures that ATP is not present to inhibit nitrogen fixation.
D) It maintains a low level of reduced cofactors.
E) It ensures that oxygen concentrations are kept low to prevent interference with enzymes.

A

E) It ensures that oxygen concentrations are kept low to prevent interference with enzymes.

50
Q

Which statement is TRUE regarding the regulation of nitrogen fixation?
A) High concentrations of ADP will activate nitrogen fixation enzymes.
B) Elevated concentrations of ammonia will reduce the expression of genes associated with nitrogen fixation.
C) ATP acts as a negative allosteric effector for nitrogenase.
D) Nitrogenase is regulated via adenylylation.
E) Oxygen acts as an allosteric effector for the nitrogenase complex.

A

B) Elevated concentrations of ammonia will reduce the expression of genes associated with nitrogen fixation.

51
Q 
What high-energy structure is found as part of the major intermediate in the glutamine synthetase reaction?
A) a phosphoanhydride bond
B) a phosphoester
C) an acyl phosphate
D) an enol
E) a thioester
A

C) an acyl phosphate

52
Q

Which statement is FALSE regarding glutamine synthetase?
A) Both Type I and Type II forms have dihedral symmetry.
B) Histidine, glycine, and alanine are all negative effectors for this enzyme.
C) It is regulated by multiple feedback inhibitors and covalent modification.
D) ATP is an inhibitor for this enzyme.
E) This enzyme is classified as a ligase.

A

D) ATP is an inhibitor for this enzyme.

53
Q

Which kind of reversible covalent modification is used to regulate glutamine synthetase?
A) ADP-ribosylation
B) adenylylation
C) phosphorylation
D) acetylation
E) both ADP-ribosylation and adenylylation

A

B) adenylylation

54
Q

Which statement is FALSE regarding the proposed mechanism for glutamine amidotransferases?
A) Part of the mechanism includes the formation of a thioester to a cysteine.
B) A hydrolysis reaction releases glutamine from the active site.
C) Ammonia is released from one substrate before reacting with the second substrate.
D) Phosphorylation is often used to activate the substrate accepting the amino group.
E) Two portions of the enzymes are connected by an “ammonia channel.”

A

B) A hydrolysis reaction releases glutamine from the active site.

55
Q

Which reaction step in the synthesis of proline is nonenzymatic?
A) the phosphorylation of the side chain
B) the reaction that generates an aldehyde product
C) the cyclization step
D) the reaction that releases inorganic phosphate as a product
E) the reaction that converts a double bond to a single bond

A

C) the cyclization step

56
Q 
Which amino acid is NOT considered to originate from alpha-ketoglutarate? 
A) arginine
B) glutamate 
C) glutamine 
D) histidine 
E) proline
A

D) histidine

57
Q 
The synthesis of methionine originates from which compound? 
A) alpha-ketoglutarate
B) 3-phosphoglycerate
C) oxaloacetate
D) pyruvate
E) ribose-5-phosphat
A

C) oxaloacetate

58
Q

Which molecule is NOT a high-energy molecule involved in the synthesis of arginine from glutamate?
A) Acetyl-CoA
B) ATP
C) NADH/NADPH
D) FADH2
E) All of these molecules are involved in this pathway.

A

D) FADH2

59
Q 
In the synthesis of serine from 3-phosphoglycerate, which answer lists the CORRECT order and type of reactions?
A) reduction, hydrolysis, transamination
B) oxidation, transamination, hydrolysis
C) reduction, transamination, hydrolysis
D) oxidation, hydrolysis, transamination
E) hydrolysis, transamination, reduction
A

B) oxidation, transamination, hydrolysis

60
Q

Which statement is FALSE regarding the synthesis of glycine from 3-phosphoglycerate (3PG)?
A) Oxidation of 3PG creates an -keto acid.
B) Pyridoxal phosphate is a required cofactor for this process.
C) The uncommon amino acid phosphoserine is an intermediate in the process.
D) A dehydration reaction produces glycine from serine.
E) A phosphatase catalyzes one of the reaction steps.

A

D) A dehydration reaction produces glycine from serine.

61
Q

Which statement is NOT a similarity in the synthesis of isoleucine, valine, and leucine?
A) Pyruvate is the starting compound for the synthesis of all these amino acids.
B) Pyridoxal phosphate is a required cofactor in the synthesis of all these amino acids.
C) These are all essential amino acids in humans.
D) An alpha-keto acid is the immediate precursor for all three synthetic pathways.
E) Acetyl-CoA is required as a substrate in all three synthetic pathways.

A

E) Acetyl-CoA is required as a substrate in all three synthetic pathways.

62
Q 
Phosphocreatine is derived from which amino acid? 
A) alanine
B) arginine 
C) cysteine 
D) serine 
E) lysine
A

B) arginine

63
Q

Which molecule does NOT require 5-phosphoribosyl-1-pyrophosphate (PRPP) as a substrate for biosynthesis?
A) adenosine monophosphate
B) cytidine monophosphate
C) guanosine monophosphate
D) histidine
E) All of these molecules require PRPP for biosynthetic pathways.

A

E) All of these molecules require PRPP for biosynthetic pathways.

64
Q

Which statement is FALSE regarding aspartate transcarbamoylase (ATCase) in prokaryotes?
A) This enzyme catalyzes the rate-limiting step in cytidine biosynthesis.
B) This enzyme is inhibited by pyrimidine triphosphates.
C) Aspartate is a homotropic activator for ATCase.
D) CTP is a heterotropic inhibitor for ATCase.
E) ATCase is regulated by product inhibition.

A

E) ATCase is regulated by product inhibition.

65
Q

Which statement is TRUE regarding Class I ribonucleotide reductase?
A) The beta subunit contains the regulatory sites for the enzyme.
B) The alpha subunit contains the active site cysteines.
C) The alpha subunit contains the binuclear iron center.
D) This enzyme catalyzes a hydrolysis reaction.
E) ATP is an inhibitor for most isoforms of this enzyme.

A

B) The alpha subunit contains the active site cysteines.

66
Q 
In purine biosynthesis, which ring nitrogens are contributed by the sidechain of glutamine?
A) N1 only
B) N1 and N3
C) N1, N3, and N9
D) N1 and N9
E) N3 and N9
A

E) N3 and N9

67
Q 
Which process below is NOT required in the conversion of dCTP into dTTP?
A) deamination
B) methylation
C) phosphate hydrolysis
D) phosphate addition
E) reduction
A

E) reduction

68
Q 
Degradation of purines in primates leads to the formation of what major excreted product?
A) allantoin
B) ammonia
C) hypoxanthine
D) urea
E) uric acid
A

E) uric acid

69
Q

Which statement is TRUE regarding the conversion of UTP into CTP by cytidylate synthetase?
A) Glutamate is also a substrate for this reaction.
B) This reaction consumes one phosphoanhydride bond.
C) This enzyme is an isomerase.
D) Ammonia is a substrate for the overall reaction.
E) Folate is a required cofactor for the reaction.

A

B) This reaction consumes one phosphoanhydride bond.

Biochemistry (6 decks)

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