Question 1

Ornithine serves 3 metabolically important roles,but is not found in proteins.Which of the following is one of the important roles of ornithine?

Accepted Answer

A)  precursor in the synthesis of aspartate
B)  an intermediate in the urea cycle
C)  formation of ornithine from serine
D)  condenses with aspartate to form argininosuccinateE) A) and D)
F) A) and C)

Question 2

Which of the following amino acid's carbon and nitrogen atoms are all used in the biosynthesis of ornithine?

Accepted Answer

A)  proline
B)  valine
C)  alanine
D)  glutamateE) B) and D)
F) A) and C)

Question 3

Which of the following is related to elevated level of homocysteine in the blood?

Accepted Answer

A)  excess folic acid
B)  homocystinuria at very low levels
C)  lower risk of heart attack and stroke
D)  folic acid-dependent conversion of homocysteine to methionineE) None of the above
F) All of the above

Question 4

The reaction,2 NH₄⁺ + α-ketoglutarate + NADPH + ATP →glutamine + NADP⁺ + ADP + Pᵢ + H₂O,is the combined result of which of the following two enzymes?

Accepted Answer

A)  glutamate dehydrogenase and glutamine synthetase
B)  nitrogenase and glutamate dehydrogenase
C)  glutamine synthetase and nitrogenase
D)  α-ketoglutarate dehydrogenase and glutamate synthetaseE) B) and C)
F) A) and B)

Question 5

Which of the following molecules is synthesized using chorismate as a precursor?

Accepted Answer

A)  threonine
B)  homocysteine
C)  tyrosine
D)  alanineE) A) and C)
F) A) and D)

Question 6

Which of the following is NOT a characteristic feature of ATP:GS:adenylyl transferase (AT) ?

Accepted Answer

A)  It catalyzes the adenylation of glutamine synthetase.
B)  It exists in 2 forms,PIIA and PIID.PIIA causes the deadenylation of glutamine synthetase,and its activity increases with an increase in glutamine.
C)  AT:PIIA needs ATP to complete the reaction.
D)  It is an enzyme that causes the adenylation/deadenylation of a specific tyrosine residue.E) A) and C)
F) B) and C)

Question 7

Which of the following amino acid carbon skeletons converges to pyruvate?

Accepted Answer

A)  methionine
B)  isoleucine
C)  glutamate
D)  cysteineE) A) and B)
F) A) and C)

Question 8

Herbicides (e.g.,"Roundup") inhibit biosynthesis of "essential" amino acids.Which of the following explains why these herbicides,however,relatively safe for animal exposure?

Accepted Answer

A)  They lack the enzymes for photosynthesis.
B)  They lack the enzymes for the glyoxylate cycle.
C)  They lack the enzymes for the glutamine synthesis pathway .
D)  They lack the enzymes for the Phe,Val,Leu,Ile,and His biosynthetic pathways.E) B) and C)
F) A) and D)

Question 9

Which of the following amino acids are referred to as the ketogenic amino acids?

Accepted Answer

A)  those that are precursors for glucose synthesis
B)  those degraded to yield acetyl-CoA or acetoacetate
C)  those that cannot be converted to fatty acids or ketone bodies
D)  those degraded to yield succinyl-CoA,pyruvate,a-ketoglutarate,fumarate,and oxaloacetateE) B) and D)
F) All of the above

Question 10

Which of the following is a characteristic of phenylketonuria?

Accepted Answer

A)  urine turning dark on standing due to air oxidation
B)  deficiency or defect in phenylalanine hydroxylase
C)  treated by putting patient on a diet high in phenylalanine
D)  treated patients suffering severe mental retardationE) C) and D)
F) All of the above

Question 11

Which of the following is a requirement of all N₂-fixing systems?

Accepted Answer

A)  the enzyme nitrogenase
B)  GTP
C)  H₂Ofree conditions
D)  a strong oxidizer such as ferredoxinE) A) and D)
F) C) and D)

Question 12

Which of the following molecules is transaminated to form aspartate?

Accepted Answer

A)  asparagine
B)  aspartame
C)  oxaloacetate
D)  α-ketoglutarateE) A) and B)
F) None of the above

Question 13

Which of the following describes how homoserine and homocysteine are related to serine and cysteine,respectively?

Accepted Answer

A)  They have an extra amino group.
B)  They have an additional methylene group.
C)  They have an additional carboxyl group.
D)  They have an aldehyde group.E) B) and D)
F) None of the above

Question 14

Which of the following explains why animals totally dependent on plants and microorganisms for nitrogen fixation and nitrate assimilation?

Accepted Answer

A)  They lack the enzyme aminotransferase.
B)  They lack the enzymes to reduce N₂ and NO₃- to NH₄⁺.
C)  They lack carbamoyl-phosphate synthetase I.
D)  They lack glutamate dehydrogenase.E) A) and B)
F) A) and C)

Question 15

Which of the following serves directly as one of the nitrogen atoms of a urea molecule?

Accepted Answer

A)  the amide N of Asn
B)  the N of Asp
C)  the R-group N of Lys
D)  the N of glucosamineE) B) and C)
F) A) and B)

Question 16

Which of the following amino acids is biosynthesized from aspartate?

Accepted Answer

A)  serine
B)  glycine
C)  cysteine
D)  lysineE) A) and B)
F) All of the above

Question 17

Which of the following regarding the process of transamination is correct?

Accepted Answer

A)  The coenzyme needed is thiamine pyrophosphate (TPP) .
B)  It is characterized by the transfer of an α-carboxyl group from an amino acid to the α-keto position of an α-keto acid.
C)  The amino donor becomes an α-keto acid.
D)  Humans are capable of synthesizing the α-keto acid analog of essential amino acids and using transamination to form the amino acids,but are not able to construct carbon skeletons of the non-essential amino acids.E) A) and C)
F) B) and C)

Question 18

Which of the following compounds is reduced to ammonia during the second step of nitrate assimilation?

Accepted Answer

A)  nitrogen
B)  carbon
C)  nitrite
D)  carbon dioxideE) A) and D)
F) C) and D)

Question 19

Which of the following describes the role ATP plays in the nitrogenase complex?

Accepted Answer

A)  breaks the N₂ triple bond
B)  provides electrons
C)  phosphorylates the enzyme
D)  transfers electrons from ferredoxinE) A) and B)
F) A) and C)

Question 20

Which of the following reactions are denitrifying bacteria NOT capable of?

Accepted Answer

A)  reducing NO₃- to N₂
B)  using NO₃- as an electron acceptor in their energy-producing pathways
C)  oxidizing NH₄⁺ to NO₃-
D)  reducing the combined-nitrogen levelsE) All of the above
F) None of the above

Exam 23: Nitrogen Acquisition and Amino Acid Metabolism

Which of the following amino acids is biosynthesized from aspartate?

Correct AnswerverifiedShow Answer

Ornithine serves 3 metabolically important roles,but is not found in proteins.Which of the following is one of the important roles of ornithine?

Correct AnswerverifiedShow Answer

Which of the following is a characteristic of phenylketonuria?

Correct AnswerverifiedShow Answer

Which of the following is a requirement of all N₂-fixing systems?

Correct AnswerverifiedShow Answer

The reaction,2 NH₄⁺ + α-ketoglutarate + NADPH + ATP →glutamine + NADP⁺ + ADP + Pᵢ + H₂O,is the combined result of which of the following two enzymes?

Correct AnswerverifiedShow Answer

Which of the following regarding the process of transamination is correct?

Correct AnswerverifiedShow Answer

Which of the following explains why animals totally dependent on plants and microorganisms for nitrogen fixation and nitrate assimilation?

Correct AnswerverifiedShow Answer

Which of the following molecules is transaminated to form aspartate?

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Which of the following describes the role ATP plays in the nitrogenase complex?

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Which of the following describes how homoserine and homocysteine are related to serine and cysteine,respectively?

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Which of the following amino acid's carbon and nitrogen atoms are all used in the biosynthesis of ornithine?

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Which of the following serves directly as one of the nitrogen atoms of a urea molecule?

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Which of the following reactions are denitrifying bacteria NOT capable of?

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Which of the following compounds is reduced to ammonia during the second step of nitrate assimilation?

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Which of the following is related to elevated level of homocysteine in the blood?

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Which of the following molecules is synthesized using chorismate as a precursor?

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Which of the following is NOT a characteristic feature of ATP:GS:adenylyl transferase (AT) ?

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Which of the following amino acid carbon skeletons converges to pyruvate?

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Which of the following amino acids are referred to as the ketogenic amino acids?

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Herbicides (e.g.,"Roundup") inhibit biosynthesis of "essential" amino acids.Which of the following explains why these herbicides,however,relatively safe for animal exposure?

Correct AnswerverifiedShow Answer

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