ABI 103 Chapter 21: Amino Acid Metabolism

_____ are involved in the nonselective degradation of proteins in well nourished cells.

Lysosomes

ATP-dependent degradation of ubiquitinated proteins is mediated by ______.

26S proteasome

Aminotransferases utilize a coenzyme synthesized from ______.

Vitamin B6

A phenomenon in which intermediates are directly transferred from one active site to another is ______.

channeling

The amino acid ______ has been thought to act as a transfer system for NH3, safely allowing the toxic molecule to be transported from the liver to the kidneys.

glutamate

The cofactor ______ is used to transfer C1 units such as methyl, formyl, and methenyl groups.

THF

The enzyme ______ is critical to regulating nitrogen metabolism.

glutamine synthetase

Infants who cannot properly degrade bilirubin develop ______.

jaundice

Organisms known as _____ can fix nitrogen into metabolically useful molecules.

diazotrophs

Which of the following describes the steps required prior to ATP-dependent degradation of proteins?
I. Ubiquitin is transferred to cysteine on a ubiquitin-conjugating enzyme.
II. The protein is linked to at least four tandemly linked ubiquitin units.
III.

B) IV, I, III, II

The majority of amino acids are deaminated by a ______ reaction.
A) transaminmation
A) reduction
B) condensation
C) transacetylation
D) oxidation

A) transaminmation

The aminotransferase reaction, in which an enzyme-PLP Schiff base forms,
I. is ATP dependent.
II. results in formation of a hydroxylaldehyde. III. results in formation of an ?-ketoacid.
IV. requires an active site lysine.
A) I, III, IV
B) I, IV
C) II, III

A) I, III, IV

Which of the following reaction sequences could result in glucose synthesis?
A) fumarate --> arginine --> urea
B) fumarate --> malate --> oxaloacetate
C) citrulline --> urea --> aspartate
D) urea --> arginine --> ornithine
E) none of the above

B) fumarate --> malate --> oxaloacetate

Ketogenic amino acids can be converted to
I. glucose
II. fatty acids
III. ketone bodies IV. pyruvate
A) I, III
B) II, IV
C) I, II
D) ?,??, ???
E) I, IV

B) II, IV

The amino acids Ala, Cys, Gly, Ser, and Thr are all degraded to the metabolic intermediate ___ and are considered ____.
A) acetyl-CoA; glucogenic
B) acetyl-CoA; ketogenic
C) pyruvate; glucogenic
D) pyruvate; ketogenic
E) acetoacetate; ketogenic

C) pyruvate; glucogenic

Which of the following glycolytic intermediates is the common precursor to serine, cysteine, and glycine?
A) fructose-6-phosphate
B) glyceraldehyde-3-phosphate
C) dihydroxyacetone phosphate
D) 3-phosphoglycerate
E) pyruvate

D) 3-phosphoglycerate

The neurotransmitters, dopamine, epinephrine, and norepinephrine are synthesized from the amino acid
A) tryptophan
B) tyrosine
C) glutamate
D) aspartate
E) lysine

B) tyrosine

Nitrogenase
I. can be found in most bacteria and a few invertebrate animals. II. contains unique redox centers that contain both Fe and Mo. III. changes in conformation as a result of ATP hydrolysis.
IV. carries out a reaction that reduces nitrogen to NO.

C) II, III

The total cost of nitrogen reduction is ____ and ___ transferred electrons.
A) 8 ATP; 4
B) 12 ATP; 8
C) 12 ATP; 6
D) 16 ATP; 8
E) 16 ATP; 6

D) 16 ATP; 8

The lifetime of a protein in cells actively involved in metabolism
A) is longer in eukaryotes than in prokaryotes.
B) ranges from months to years.
C) is independent of the function and activity of the protein.
D) can change in response to changes in metab

D) can change in response to changes in metabolic hormone levels.

What are KFERQ proteins?
I. Proteins that contain the KFERQ pentapeptide sequence (or a similar sequence).
II. Proteins that are selectively degraded in tissues that atrophy after a prolonged fast (starvation).
III. A special set of enzymes that are activ

A) I, II

Proteins targeted for destruction via the ubiquitin pathway include
I. proteins with a destabilizing N-end rule component.
II. proteins with a PEST sequence.
III. proteins that contain the RING finger E3 component named E3a. IV. protein with polyubiquitin

D) I, II, IV

The presence of SGOT and SGPT in the serum indicate potential
A) starvation and brain tissue damage.
B) inflammation.
C) heart attack or liver damage.
D) lung or breast cancer.
E) none of the above

C) heart attack or liver damage.

Oxidative deamination of glutamate
I. generates NAD(P)H and ?-ketoglutarate.
II. is inhibited by glutamate.
III. is activated by GTP.
IV. eliminates the keto group from ?-ketoacids.
A) I only
B) I, II
C) I, III
D) II, IV
E) III, IV

A) I only

Which of the following statements about maple syrup urine disease is FALSE?
I. It is caused by a genetic deficiency in the enzyme BCKDH.
II. The disease is fatal unless promptly treated.
III. There is a buildup of the branched-chain ?-keto acids.
IV. Pati

E) All of the statements are true.

Which of the following statements about phenylalanine is(are) TRUE?
A) The enzymatic degradation of phenylalanine requires the biopterin cofactor.
B) Individuals with defects in phenylalanine catabolism require tyrosine in their
diet.
C) An inability to h

D) A and C

Which of the following statements about tryptophan synthase is FALSE?
A) Indole can pass between active sites via a channel in the enzyme.
B) Tryptophan synthase catalyzes two distinct reaction steps to form tryptophan.
C) The enzyme is a tetramer of four

C) The enzyme is a tetramer of four identical subunits.

Heme biosynthesis
A) requires that synthesis of the protoporphryin ring occur in the mitochondria due to difficulties in transporting large molecule.
B) is inhibited in lead poisoning.
C) can be completed using enzymes from the cytosol.
D) A and B
E) A, B

B) is inhibited in lead poisoning.

_____ catalyzes the synthesis of ____, a molecule that signals vasodilation, from the
precursor _____
A) NOS; nitric oxide (NO); arginine
B) Nitrous oxidase; nitrous oxide; arginine
C) Arginate; nitric oxide (NO); citrulline
D) Citrulline dehydrogenase; n

A) NOS; nitric oxide (NO); arginine

Which of the following is(are) advantages to the constant degradation and reformation of proteins?
A) Nutrients can be stored as proteins, which can be used during periods of metabolic need.
B) Damaged proteins are eliminated so they do not accumulate.
C)

D) All of the above are advantages.

The activity of bacterial glutamine synthetase is
I. inhibited allosterically by tryptophan.
II. inhibited allosterically by glucosamine-6-phosphate. III. activated by nine allosteric feedback inhibitors.
IV. altered by covalent modification.
A) I, III
B)

E) I, II, III, IV

Which enzyme catalyses a reaction via an enzyme-bound adenylated intermediate?
A) glutamine synthetase
B) argininosuccinate synthetase
C) carbamoyl phosphate synthetase I
D) Ac-CoA decarboxylase
E) arginase

B) argininosuccinate synthetase

In which cellular location listed below does the following reaction take place? arginine ? urea + ornithine
A) cytosol
B) mitochondrial matrix
C) lysosome
D) AorB
E) none of the above

A) cytosol

In which cellular location listed below does the following reaction take place?
ornithine + carbamoyl-phosphate ? citrulline
A) cytosol
B) mitochondrial matrix
C) lysosome
D) AorB
E) none of the above

B) mitochondrial matrix

What species are combined to produce carbamoyl phosphate?
A) NH3 , PO43?, HCO3?
B) NH4+, PO43?, Ac-CoA, releasing CoA-SH
C) glycine & inorganic phosphate, releasing CO2
D) acetate & NH4+, releasing CO2
E) alanine & inorganic phosphate, releasing acetate

A) NH3 , PO43?, HCO3?

A number of compounds, including neurotransmitters, are synthesized from amino acids via decarboxylations. The enzymes catalyzing these steps usually use _______ as a cofactor.
A) pyridoxal-5?-phosphate
B) thiamine pyrophosphate
C) biotin
D) cobalt contai

A) pyridoxal-5?-phosphate

Which of the following is TRUE regarding catabolism of leucine?
A) The pathway begins with aspartate.
B) The pathway requires ?-ketoglutarate.
C) The pathway requires TPP.
D) The pathway generates HMG-CoA.
E) none of the above

B) The pathway requires ?-ketoglutarate.

The metabolite chorismate
A) allosterically enhances production of aromatic amino acids.
B) is an important intermediate in the production of Trp, Tyr, and Phe.
C) is a derivative of glucose.
D) A and B
E) B and C

E) B and C

The pictured compound, glutamate-5-semialdehyde, is an intermediate in the biosynthesis of which of the following amino acids?
A) histidine
B) arginine
C) methionine
D) threonine
E) More than one of the above is made from this
intermediate.

B) arginine

Which of the following amino acids is NOT synthesized from aspartate?
A) threonine
B) methionine
C) lysine
D) cysteine
E) All of the above are synthesized from aspartic acid.

D) cysteine

Which of the following is TRUE about glutamine?
I. It is formed from ?-ketoglutarate.
II. It donates an amino group to aspartate to form asparagine. III. It is directly required for ornithine synthesis.
IV. It is a precursor to homoserine.
A) I, II
B) I,

A) I, II

Individuals with an alanine to valine mutation in N5, N10 - methylenetetrahydrofolate reductase (MTHFR)
I. typically have higher levels of homocysteine.
II. have increased risk for cardiovascular disease.
III. typically have increased incidence of oxidati

E) I, II, III, IV

Which of the following control the urea cycle?
I. substrate concentration of the cycle enzymes
II. allosteric activation of carbamoyl phosphate synthetase I III. concentration of glutamate
IV. availability of glucose
A) I, III
B) II, III
C) II, IV
D) I, I

D) I, II, III

Enzyme A is involved in the metabolism of metabolite C to metabolite D. Enzyme A is part of a linear pathway involving ten enzymes ultimately converting B F. High levels of F directly alter the activity of enzyme A and result in control over the overall p

A) likely has high rates of degradation and synthesis.

Which of the following is required for synthesis of tryptophan?
A) serine
B) phosphoenolpyruvate
C) erythrose-4-phosphate
D) all of the above
E) none of the above

D) all of the above

A mutation in GDH of patients with HI/HA (hypoglycemia/hyperammonemia) results in a decrease in allosteric control of GDH via GTP. Which of the following will be observed in the patients?
A) an increase in ammonia
B) an increase in glutamate
C) an increas

E) A and C

Which of the following require a cyclic carbohydrate precursor for synthesis?
I. histidine II. alanine III. arginine IV. tyrosine
A) I, II
B) II only
C) I, III
D) I , IV
E) II, IV

D) I , IV

Which of the following are essential amino acids for adult humans?
A) Arg, His, Gly, Try
B) Met, Lys, His, Val
C) His, Leu, Tyr, Ala
D) Met, Gly, Thr, Ser
E) Ala, Arg, Cys, Ser

B) Met, Lys, His, Val

The synthesis of which of the following uses an aminotransferase in the first step of the synthesis?
A) glutamine
B) proline
C) serine
D) valine
E) all of the above

A) glutamine

Which of the following amino acid breakdown reactions would be catalyzed by an aminotransferase?
A) Threonine --> Acetyl CoA
B) Alanine --> Pyruvate
C) Asparagine --> Aspartate
D) Homocysteine --> Methionone
E) HMG-CoA --> Acetoacetate

B) Alanine --> Pyruvate

Individuals with an alanine to valine mutation in N5, N10 - methylenetetrahydrofolate reductase (MTHFR)
I. typically have higher levels of homocysteine.
II. have increased risk for cardiovascular disease.
III. typically have increased incidence of oxidati

...

Which of the following control the urea cycle?
I. substrate concentration of the cycle enzymes
II. allosteric activation of carbamoyl phosphate synthetase I III. concentration of glutamate
IV. availability of glucose
A) I, III
B) II, III
C) II, IV
D) I, I

...

Enzyme A is involved in the metabolism of metabolite C to metabolite D. Enzyme A is part of a linear pathway involving ten enzymes ultimately converting B F. High levels of F directly alter the activity of enzyme A and result in control over the overall p

...

Which of the following is required for synthesis of tryptophan?
A) serine
B) phosphoenolpyruvate
C) erythrose-4-phosphate
D) all of the above
E) none of the above

...

Individuals with an alanine to valine mutation in N5, N10 - methylenetetrahydrofolate reductase (MTHFR)
I. typically have higher levels of homocysteine.
II. have increased risk for cardiovascular disease.
III. typically have increased incidence of oxidati

...

ATP-dependent degradation of ubiquitinated proteins is mediated by ______.

...

Aminotransferases utilize a coenzyme synthesized from ______.

...

A phenomenon in which intermediates are directly transferred from one active site to another is ______.

...

The amino acid ______ has been thought to act as a transfer system for NH3, safely allowing the toxic molecule to be transported from the liver to the kidneys.

...

The cofactor ______ is used to transfer C1 units such as methyl, formyl, and methenyl groups.

...

The enzyme ______ is critical to regulating nitrogen metabolism.

...

Infants who cannot properly degrade bilirubin develop ______.

...

Organisms known as _____ can fix nitrogen into metabolically useful molecules.

...

ATP-dependent degradation of ubiquitinated proteins is mediated by ______.

...

Aminotransferases utilize a coenzyme synthesized from ______.

...

A phenomenon in which intermediates are directly transferred from one active site to another is ______.

...

The amino acid ______ has been thought to act as a transfer system for NH3, safely allowing the toxic molecule to be transported from the liver to the kidneys.

...

The cofactor ______ is used to transfer C1 units such as methyl, formyl, and methenyl groups.

...

The enzyme ______ is critical to regulating nitrogen metabolism.

...

ATP-dependent degradation of ubiquitinated proteins is mediated by ______.

...

Aminotransferases utilize a coenzyme synthesized from ______.

...

A phenomenon in which intermediates are directly transferred from one active site to another is ______.

...

ATP-dependent degradation of ubiquitinated proteins is mediated by ______.

...