Deck 23: Nitrogen Acquisition and Amino Acid Metabolism

Question 1

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

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.

Answer 1

B

Question 2

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

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

Answer 2

A

Question 3

Which of the following describes the role of N-acetylglutamate in the incorporation of ammonium into metabolic intermediates?

A)coenzyme for glutamine synthetase (GS)
B)competitive inhibitor for glutamine synthetase (GS)
C)allosteric activator for carbamoyl-phosphate synthetase I (CPS-I)
D)substrate for the amination of the g-glutamyl-phosphate

Answer 3

C

Question 4

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

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 levels

Question 5

Which of the following describes the process of nitrogen fixation?

A)the reduction of NO₃- to NH₄⁺
B)the formation of NH₄⁺ from N₂ gas
C)the oxidation of NH₄⁺ to N₂ gas
D)the oxidation of NH₄⁺ to NO₃-

Question 6

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

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.

Question 7

Which of the following describes how control over nitrogenase activity accomplished?

A)NH₄⁺ prevents expression of the genes that encode nitrogenase.
B)ATP serves as an allosteric activator.
C)AMP serves as an allosteric inhibitor.
D)Phosphorylation prevents activity.

Question 8

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

A)glutamate dehydrogenase and glutamine synthetase
B)nitrogenase and glutamate dehydrogenase
C)glutamine synthetase and nitrogenase
D)a-ketoglutarate dehydrogenase and glutamate synthetase

Question 9

Which of the following enzymes catalyzes the reaction below?
Glutamate + NAD(P)⁺ + H₂O à NH₄⁺ + a-ketoglutarate + NAD(P)H + H⁺

A)nitrogenase
B)carbamoyl-phosphate synthetase (CPS-I)
C)glutamine synthetase (GS)
D)glutamate dehydrogenase (GDH)

Question 10

Which of the following explains why bacterial glutamine synthetase monomers are inactive?

A)They must be phosphorylated for activity.
B)They must be activated by binding glutamine.
C)They must be stacked for interface active site development.
D)They must be combined for allosteric regulation.

Question 11

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

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

Question 12

Which of the following acts in feedback inhibition of glutamine synthetase in prokaryotes?

A)proline
B)ATP
C)glucose-6-phosphate
D)histidine

Question 13

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

A)nitrogen
B)carbon
C)nitrite
D)carbon dioxide

Question 14

Which of the following compounds is involved in electron transport carried out by nitrate reductase?

A)NADH
B)FMN
C)MoCo
D)CO₂

Question 15

Which of the following compounds provides the 6 electrons required by nitrite reductase to reduce NO₂⁻ to NH₄⁺ in higher plants?

A)plastoquinone
B)heme
C)CO₂
D)ferredoxin

Question 16

Which of the following identifies where nitrifying bacteria obtain their chemical energy?

A)from the formation of NH₄⁺ from N₂ gas
B)from the oxidation of NH₄⁺ to N₂
C)from the oxidation of NH₄⁺ to NO₃-
D)from the formation of NO₂- from NO₃-

Question 17

Which of the following classes of enzymes does glutamine synthetase belong to?

A)isomerase
B)oxidoreductase
C)ligase
D)transferase

Question 18

Which of the following reactions is catalyzed by glutamate dehydrogenase catalyze?

A)the reductive amination of a-ketoglutarate to yield glutamate
B)phosphorylation of carbamate to yield carbamoyl phosphate
C)the amidation of the g-carboxyl group of glutamate to form glutamine
D)the deadenylation of glutamine synthetase

Question 19

Which of the following products is formed from the glutamate synthase-catalyzed reaction?

A)glutamate
B)a-ketoglutarate
C)NADPH
D)N-acetylglutamate

Question 20

Which of the following enzymes catalyzes the reaction below?
N₂ + 10 H⁺+ 8 e⁻ à 2 NH₄⁺ + H₂

A)nitrate reductase
B)nitrogenase
C)glutamate dehydrogenase
D)glutamate synthase

Question 21

How are glutamic acid,glutamine,proline,and arginine related to the process of amino acid biosynthesis?

A)They are all derived from a-ketoglutarate.
B)They are all derivatives of acetyl-CoA.
C)They are all derivatives of pyruvate.
D)They are all derived from aspartate.

Question 22

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

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 argininosuccinate

Question 23

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

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.

Question 24

The structural difference between serine and homoserine is the same as the structural difference between cysteine and homocysteine.How are homoserine and homocysteine different from their commonly occurring amino acid partners?

A)1 additional -CH₂- group
B)1 additional -COOH group
C)1 additional -NH₂ group
D)2 additional -NH₂ groups

Question 25

Which of the following molecules is transaminated to form aspartate?

A)asparagine
B)aspartame
C)oxaloacetate
D)a-ketoglutarate

Question 26

Which of the following amino acids is classified as an essential amino acid?

A)proline
B)valine
C)glutamine
D)aspartate

Question 27

Which of the following amino acids is formed by transamination of pyruvate with glutamate?

A)alanine
B)serine
C)cysteine
D)aspartate

Question 28

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

A)threonine
B)homocysteine
C)tyrosine
D)alanine

Question 29

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

A)The coenzyme needed is thiamine pyrophosphate (TPP).
B)It is characterized by the transfer of an a-carboxyl group from an amino acid to the a-keto position of an a-keto acid.
C)The amino donor becomes an a-keto acid.
D)Humans are capable of synthesizing the a-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.

Question 30

Which of the following compounds is an intermediate in biosynthesis of ornithine and a regulator of carbamoyl-phosphate synthetase-I?

A)g-glutamyl-phosphate
B)a-ketoglutarate
C)N-acetylglutamate
D)glutamine-5-phosphate

Question 31

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

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 methionine

Question 32

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

A)the amide N of Asn
B)the N of Asp
C)the R-group N of Lys
D)the N of glucosamine

Question 33

Which of the following regarding the 3-phosphoglycerate family is correct?

A)Production of glycine also produces N5,N10-methylene-THF,which is important in the biosynthesis of purines.
B)3-PG is diverted from glycolysis by phosphoglycerate mutase.
C)Serine,glycine,and methionine are all non-essential amino acids.
D)Glycine production is regulated by a direct feedback mechanism.

Question 34

Which of the following regarding the urea cycle is correct?

A)Stimulation of carbamoyl-phosphate synthetase I (CPS-I)decreases the activity of the urea cycle.
B)It results in the accumulation of excess nitrogen.
C)It is linked to the citric acid cycle through citrate.
D)It is completed by the regeneration of ornithine from arginine.

Question 35

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

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.

Question 36

Which of the following is a commonly used transamination pair?

A)Asp / oxaloacetate
B)Phe / phenylpyruvate
C)Glu / pyruvate
D)Ala / a-ketoglutarate

Question 37

Which of the following amino acids is biosynthesized from aspartate?

A)serine
B)glycine
C)cysteine
D)lysine

Question 38

Which of the following outcomes would be a result of a high [Gln]/[a-KG] ratio?

A)a need for ammonium fixation by glutamine synthetase
B)an increase in activity of glutamine synthetase
C)an increase in the degree of adenylation of glutamine synthetase
D)inhibition of AT:PIIA and stimulation of AT:PIID

Question 39

Which of the following molecules is synthesized and then transaminated using glutamate,for subsequent use in amino acid biosynthesis in plants and microorganisms?

A)an a-keto acid
B)an acetyl-CoA derivative
C)a phospho-carbon skeleton
D)a nitrogenous base

Question 40

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

A)proline
B)valine
C)alanine
D)glutamate

Question 41

Which of the following molecules is NOT a convergent metabolic intermediate of a-amino acid carbon skeletons?

A)citrate
B)a-ketoglutarate
C)oxaloacetate
D)succinyl-CoA

Question 42

Which of the following is NOT a part of the degradation pathway of valine,isoleucine,and methionine leading to succinyl-CoA?

A)biotin and ATP
B)acetyl-CoA
C)methylmalonyl-CoA
D)propionyl-CoA

Question 43

Which of the following is a characteristic of maple syrup urine disease?

A)non-hereditary enzyme defect
B)decreased levels of Val,Leu,and Ile and their corresponding a-keto acids in blood and urine
C)elevated blood levels of acetoacetate and b-hydroxybutyrate
D)fatal without detection and treatment

Question 44

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

A)methionine
B)isoleucine
C)glutamate
D)cysteine

Question 45

Which of the following is a characteristic of phenylketonuria?

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 retardation

Question 46

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

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 oxaloacetate

Question 47

Which of the following is NOT a characteristic of alkaptonuria?

A)excretion of homogentisate
B)urine turning dark on standing due to air oxidation
C)possibility of arthritis due to accumulation of homogentisate in joints
D)possibility of mental retardation due to accumulation of Phe metabolites