Exam Questions - Lesson 3 - Metabolism of Proteins & Amino Acids - Harper’s Illustrated Biochemistry, 29th Edition (2012)

Harper’s Illustrated Biochemistry, 29th Edition (2012)

SECTION III. Metabolism of Proteins & Amino Acids

Exam Questions

Section III

1. Select the one of the following statements that is NOT CORRECT?

A. Selenocysteine is present at the active sites of certain human enzymes.

B. Selenocysteine is inserted into proteins by a posttranslational process.

C. Transamination of dietary α-keto acids can replace the dietary essential amino acids leucine, isoleucine, and valine.

D. Conversion of peptidyl proline to peptidyl 4-hydroxyproline is accompanied by the incorporation of oxygen into succinate.

E. Serine and glycine are interconverted in a single reaction in which tetrahydrofolate derivatives participate.

2. Select the one of the following statements that is NOT CORRECT?

A. Δ1-Pyrroline-5-carboxylate is an intermediate in both the biosynthesis and catabolism of L-proline.

B. Human tissues can form dietarily nonessential amino acids from amphibolic intermediates or from dietarily essential amino acids.

C. Human liver tissue can form serine from the glycolytic intermediate 3-phosphoglycerate.

D. The reaction catalyzed by phenylalanine hydroxylase interconverts phenylalanine and tyrosine.

E. The reducing power of tetrahydrobiopterin derives ultimately from NADPH.

3. Identify the metabolite that does NOT serve as a precursor of a dietarily essential amino acid:

A. α-Ketoglutarate

B. 3-Phosphoglycerate

C. Glutamate

D. Aspartate

E. Histamine

4. Select the CORRECT answer. The first reaction in the degradation of the majority of the common amino acids involves the participation of:

A. NAD+

B. Pyridoxal phosphate

C. Thiamine pyrophosphate (TPP)

D. FAD

E. NAD+ and TPP

5. Identify the amino acid that is the major contributor to hepatic gluconeogenesis.

A. Alanine

B. Glutamine

C. Glycine

D. Lysine

E. Ornithine

6. Select the one of the following statements that is NOT CORRECT?

A. The rate of hepatic gluconeogenesis from glutamine is far higher than that of any other amino acid.

B. Angelman syndrome is associated with a defective ubiquitin E3 ligase.

C. Following a protein-rich meal, the splanchnic tissues release predominantly branched-chain amino acids, which are taken up by peripheral muscle tissue.

D. The L-α-amino oxidase-catalyzed conversion of an α-amino acid to its corresponding α-keto acid is accompanied by the release of NH4+.

E. Similar or even identical signs and symptoms can be associated with different mutations of the gene that encodes a given enzyme.

7. Select the one of the following statements that is NOT CORRECT?

A. PEST sequences target some proteins for rapid degradation.

B. ATP and ubiquitin typically participate in the degradation of membrane-associated proteins and proteins with long half-lives.

C. Ubiquitin molecules are attached to target proteins via non-α peptide bonds.

D. The discoverers of ubiquitin-mediated protein degradation received a Nobel Prize.

E. Degradation of ubiquitin-tagged proteins takes place in the proteasome, a multi-subunit macromolecule present in all eukaryotes.

8. For metabolic disorders of the urea cycle, which statement is NOT CORRECT?

A. Ammonia intoxication is most severe when the metabolic block occurs prior to reaction 3 of the urea cycle, catalyzed by argininosuccinate synthase.

B. Clinical symptoms include mental retardation and the avoidance of protein-rich foods.

C. Clinical signs include hyperammonemia and respiratory acidosis.

D. Aspartate provides the second nitrogen of argininosuccinate.

E. Dietary management focuses on a low-protein diet ingested as frequent small meals.

9. Select the one of the following statements that is NOT CORRECT?

A. One metabolic function of glutamine is to sequester nitrogen in a non-toxic form.

B. Liver glutamate dehydrogenase is allosterically inhibited by ATP and activated by ADP.

C. Urea is formed both from absorbed ammonia produced by enteric bacteria and from ammonia generated by tissue metabolic activity.

D. The concerted action of glutamate dehydrogenase and glutamate aminotransferase may be termed transdeamination.

E. Fumarate generated during biosynthesis of argininosuccinate ultimately forms oxaloacetate in reactions catalyzed by mitochondrial fumarase and malate dehydrogenase.

10. Select the one of the following statements that is NOT CORRECT?

A. Histamine arises by decarboxylation of histidine.

B. Threonine provides the thioethanol moiety for biosynthesis of coenzyme A.

C. Ornithine serves as a precursor of both spermine and spermidine.

D. Serotonin and melatonin are metabolites of tryptophan.

E. Glycine, arginine, and methionine each contribute atoms for biosynthesis of creatine.

11. Select the one of the following statements that is NOT CORRECT?

A. Excreted creatinine is a function of muscle mass, and can be used to determine whether a patient has provided a complete 24-hour urine specimen.

B. Many drugs and drug catabolites are excreted in urine as glycine conjugates.

C. Decarboxylation of glutamine forms the inhibitory neurotransmitter GABA (γ-aminobutyrate).

D. The concentration of histamine in brain hypothalamus exhibits a circadian rhythm.

E. The major nonprotein metabolic fate of methionine is conversion to S-adenosylmethionine.

12. Which of the following is NOT a hemoprotein?

A. Myoglobin

B. Cytochrome c

C. Catalase

D. Cytochrome P450

E. Albumin

13. A 30-year-old male presented at clinic with a history of intermittent abdominal pain and episodes of confusion and psychiatric problems. Laboratory tests revealed increases of urinary δ-aminolevulinate and porphobilinogen. Mutational analysis revealed a mutation in the gene for uroporphyrinogen I synthase (porphobilinogen deaminase). The probable diagnosis was:

A. X-linked sideroblastic anemia.

B. Acute intermittent porphyria.

C. Congenital erythropoietic porphyria.

D. Porphyria cutanea tarda.

E. Variegate porphyria.

14. Select the one of the following statements that is NOT CORRECT?

A. Bilirubin is a cyclic tetrapyrrole.

B. Bilirubin is carried in the plasma to the liver bound to albumin.

C. High levels of bilirubin can cause damage to the brains of newborn infants.

D. Bilirubin contains methyl and vinyl groups.

E. Bilirubin does not contain iron.

15. A 62-year-old female presented at clinic with intense jaundice, steadily increasing over the preceding 3 months. She gave a history of severe upper abdominal pain, radiating to the back, and had lost considerable weight. She had noted that her stools had been very pale for some time. Lab tests revealed a very high level of direct bilirubin, and also elevated urinary bilirubin. The plasma level of alanine aminotransferase (ALT) was only slightly elevated, whereas the level of alkaline phosphatase was markedly elevated. Abdominal ultrasonography revealed no evidence of gallstones. Of the following, which is the most likely diagnosis?

A. Gilbert syndrome.

B. Hemolytic anemia.

C. Type 1 Criggler-Najjar syndrome.

D. Carcinoma of the pancreas.

E. Infectious hepatitis.