Deck 20: Metabolism of Nitrogenous Compounds I: Principles of Biosynthesis, utilization, and Turnover

Question 1

Which of the following metabolites is elevated as a result of low folate levels and poses a risk for cardiovascular disease?

A)homocysteine
B)methionine
C)5-formyl-THF
D)formate
E)none of the above

Answer 1

A

Question 2

Which of the following amino acids is exclusively ketogenic?

A)phenylalanine
B)tyrosine
C)isoleucine
D)arginine
E)leucine

Answer 2

E

Question 3

Which of the following amino acids relies upon the synthesis of carbamoyl phosphate?

A)lysine
B)histidine
C)arginine
D)glutamine
E)asparagine

Answer 3

C

Question 4

In the nitrogen fixation process,which step of the electron transfer process requires ATP hydrolysis?

A)transfer of electron from ferredoxin to the 4Fe-4S complex
B)transfer of electron from 4Fe-4S complex to the P cluster
C)transfer of electron from P cluster to iron-molybdenum cofactor (FeMo-co)
D)transfer of electron from FeMo-co to nitrogen
E)none of the above

Question 5

The reaction of ammonia with $\alpha$ -ketoglutarate is catalyzed by _________ and requires _________ as a reactant.

A)glutamate synthetase;ATP
B)glutamate synthetase;NADH or NADPH
C)glutamate dehydrogenase;ATP
D)glutamate dehydrogenase;NADH or NADPH
E)none of the above

Question 6

Ubiquitin is added to _________ residues of the target protein by reaction with the terminal __________ group of ubiquitin.

A)lysine;carboxyl
B)serine;carboxyl
C)cysteine;carboxyl
D)glutamate;amine
E)glutamine;amine

Question 7

Which of the following is seen in the transaminase mechanism?

A)aldimine formed between pyridoxal and lysine residue
B)Schiff base
C)pyridoxamine phosphate that reacts only with an $\alpha$ -ketoacid
D)a carbanion that is resonance stabilized as a quinonoid intermediate
E)all of the above

Question 8

Which of the following correctly accounts for the regulation of carbamoyl phosphate synthetase I?

A)inhibited by N-acetylglutamate,activated by acetylation of a lysine residue
B)inhibited by N-acetylglutamate,activated by phosphorylation of a tyrosine residue
C)activated by N-acetylglutamate,inhibited by acetylation of a lysine residue
D)activated by N-acetylglutamate,activated by phosphorylation of a tyrosine residue
E)none of the above

Question 9

The reaction catalyzed by nitrite reductase requires _______ electrons and is summarized as _____________.

A)2;NO₃^- $\to$ NO₂^-
B)2;NO₂^- $\to$ NO^-
C)4;NO₂^- $\to$ NO^- $\to$ NH₂OH
D)4;NO₂^- $\to$ NO^- $\to$ NH₃
E)6;NO₂^- $\to$ NO^- $\to$ NH₂OH $\to$ NH₃

Question 10

What is a PEST sequence in a protein?

A)a sequence where phosphorylation occurs at every serine and tyrosine
B)a sequence that confers resistance to cathepsin-mediated proteolysis
C)a sequence of phenylalanine-glutamate-serine-threonine that is found in many proteins with half lives less than 2 hours
D)a sequence that causes ubiquitination of the protein followed by degradation
E)none of the above

Question 11

The conversion of nitrogen to ammonia can be accomplished by _________ while the conversion of nitrate to ammonia can be accomplished by _________.

A)plants;diazotrophs
B)diazotrophs;plants
C)diazotrophs;invertebrates
D)denitrifying bacteria;bacteria
E)denitrifying bacteria;plants

Question 12

Which of the following is an essential amino acid for humans?

A)alanine
B)serine
C)tyrosine
D)cysteine
E)histidine

Question 13

Assuming that ammonia serves as the source of both nitrogen atoms of urea and that all cycles involved in the production of urea make one full turn,how many ATP equivalents and how many NADH are required to produce one molecule of urea?

A)3 ATP equivalents,1 NADH
B)3 ATP equivalents,0 NADH
C)4 ATP equivalents,1 NADH
D)4 ATP equivalents,0 NADH
E)none of the above

Question 14

Which of the following reactions is highly active in the liver when large amounts of amino acids are moving from extrahepatic tissue to the liver?

A)conversion of glutamate to glutamine
B)oxidation of glutamate by glutamate dehydrogenase
C)reduction of $\alpha$ -ketoglutarate by glutamate dehydrogenase
D)transamination of glutamate and pyruvate to $\alpha$ -ketoglutarate and alanine
E)none of the above

Question 15

What are the products of the following transamination?

A)glutamine and pyruvate
B) $\alpha$ -ketoglutarate and alanine
C)glutamate and alanine
D)oxaloacetate and alanine
E)aspartate and pyruvate

Question 16

Which of the following enzymes of ammonia incorporation is the most highly regulated?

A)glutamate dehydrogenase
B)glutamate synthetase
C)glutamine synthetase
D)glutamine synthase
E)none of the above

Question 17

Which of the following forms of tetrahydrofolate is correctly paired with the reaction for which it serves as a coenzyme?

A)5,10-methenyl-THF: biosynthesis of purines
B)5-methyl-THF: dUMP $\to$ dTMP
C)5,10-methylene-THF: glycine $\to$ serine
D)5-methyl-THF: methionine $\to$ homocysteine
E)all of the above

Question 18

Which of the following represents a correct flow of electrons for nitrogen fixation?

A)ferredoxin $\to$ Fe protein $\to$ MoFe protein $\to$ N₂
B)Fe protein $\to$ MoFe protein $\to$ ferredoxin $\to$ N₂
C)MoFe protein $\to$ Fe protein $\to$ ferredoxin $\to$ N₂
D)ferredoxin $\to$ MoFe protein $\to$ Fe protein $\to$ N₂
E)none of the above

Question 19

In the regulation of glutamine synthetase activity,an important regulatory protein,P_II exists in two states,one with UMP covalently bound (P_II-UMP),the other without (P_II).Which of the following statements regarding $\alpha$ -ketoglutarate and P_II is correct?

A) $\alpha$ -ketoglutarate binds to P_II causing inhibition of adenylyltransferase
B) $\alpha$ -ketoglutarate binds to P_II causing activation of adenylyltransferase
C) $\alpha$ -ketoglutarate binds to P_II-UMP causing inhibition of adenylyltransferase
D) $\alpha$ -ketoglutarate binds to P_II-UMP causing activation of adenylyltransferase
E) $\alpha$ -ketoglutarate does not bind to either form of P_II

Question 20

Which of the following correctly explains the covalent modification used to control glutamine synthetase?

A)uridylylation activates,deuridylylation inhibits
B)uridylylation inhibits,deuridylylation activates
C)adenylation activates,deadenylation inhibits
D)adenylation inhibits,deadenylation activates
E)phosphorylation inhibits,dephosphorylation activates

Question 21

For the following transamination reaction,show the products of the first half of the reaction.

Question 22

What would be the energy requirements of the urea cycle if both nitrogens of urea came from glutamine (assuming that any NADH made was re-oxidized via electron transport/oxidative phosphorylation)? Explain how this is possible.

Question 23

Show the products of the following reaction.

Question 24

What is the only reaction of mammalian amino acid metabolism that is dependent upon vitamin B₁₂?

A)conversion of phenylalanine to tyrosine
B)conversion of homocysteine to methionine
C)isomerization of methylmalonyl-CoA to succinyl-CoA
D)methane synthesis
E)none of the above