4. A 1-year-old Caucasian girl has had frequent wet diapers and seems to always want her bottle or cup. Her pediatrician is concerned about her growth at her 1-year well visit and notes that she had two prior hospitalizations for dehydration. The pediatrician suspects nephrogenic diabetes insipidus (MIM*125800) and orders serum electrolytes that show concentrations of sodium at 155 mEq/L (normal 133-146) and chloride at 123 (normal 98-107). Urinalysis shows a very dilute urine. Further testing involves a gene named aquaporin-2 that has several transmembrane domains demarcated by β turns. Which of the following β-turn amino acids are most likely to be mutated in patients with nephrogenic diabetes insipidus?

a. Arginine and lysine

b. Aspartic acid and glutamic acid

c. Leucine and valine

d. Glycine and proline

e. Tryptophan and tyrosine

5. A 14-year-old Hispanic adolescent presents with acute abdominal pain and is noted to have mildly yellow whites of the eyes (scleral icterus). Blood counts indicate a low hemoglobin concentration and the blood smear shows sphere-shaped instead of biconcave red blood cells. The girl’s mother reports that she, her father, and several other relatives have anemia, and that they have been diagnosed with a form of spherocytosis (MIM*182900) that is caused by mutations in the ankyrin structural protein of erythrocytes. The student on the case is asked to prepare discussion of clinical-molecular correlation on morning rounds, and downloads a diagram of ankyrin structure and amino acid sequence. The structure has domains of antiparallel α helices, which facilitate stacking of ankyrins into ordered arrays. As the student attempts correlation of ankyrin sequence and structure, α-helical domains could be best identified by the absence of which of the following amino acids?

a. Alanine

b. Cysteine

c. Histidine

d. Proline

e. Glycine

6. A 1-year-old Caucasian girl presents to a pediatrician after being removed from her parents because of severe neglect. The pediatrician notes the child is undersized with tissue and muscle wasting, loss of adipose tissue, mild acidosis, and a hopeless, depressed look. Malnutrition is recognized and supported with laboratory studies that include a low serum protein concentration. The pediatrician institutes a gradual regimen of increased calories and nutrition, gradual because rapid feeding will produce diarrhea, worsening edema, and further protein loss. The extra tissue fluid (edema) and acidosis demonstrate the importance of proteins in maintaining tissue hydration and pH. Indicate the child’s disease and which protein amino acids would have the greatest buffering capacity at physiologic pH.

a. Kwashiorkor; lysine

b. Marasmus; histidine

c. Kwashiorkor; aspartic acid

d. Marasmus; valine

e. Kwashiorkor; leucine

7. A 1-year-old Caucasian boy presents with several fractures, and a protective services investigation ensues. Laboratory evaluation shows mild anemia, a serum pH of 7.2, and a urine pH that is anomalously high at 8.5. Review of the radiographs shows some increased bone density of the skull and limbs, and the diagnosis is changed from battered child to a form of osteopetrosis (MIM*259730). This condition is caused by a nonfunctional mutation in the gene for one form of carbonic anhydrase, the enzyme catalyzing reversible hydration of carbon dioxide The discrepant blood and urine pH values in the patient are best explained by which of the following?

a. Decreased renal carbonic anhydrase with increased conversion and excretion of bicarbonate in urine

b. Increased renal carbonic anhydrase with reduced conversion and excretion of bicarbonate into urine

c. Decreased renal carbonic anhydrase with reduced formation and excretion of hydrogen ion into urine

d. Decreased renal carbonic anhydrase with increased formation and excretion of hydrogen ion into urine

e. Increased renal carbonic anhydrase with reduced formation and excretion of hydrogen ion into urine

8. A 60-year-old Caucasian male is brought to his physician from an institution for severe mental deficiency. The physician reviews his family history and finds he has an older sister in the same institution. Their parents are deceased but reportedly had normal intelligence and no chronic diseases. The man sits in an odd position as though he was sewing, prompting the physician to obtain a ferric chloride test on the man’s urine. This test turns color with aromatic (ring) compounds, including certain amino acids, and a green color confirms the physician’s diagnosis. Which of the following amino acids was most likely detected in the man’s urine?

a. Glycine

b. Serine

c. Glutamine

d. Phenylalanine

e. Methionine

9. A 2-year-old Caucasian boy is admitted for failure to gain weight. His hair has turned reddish brown and his extremities are swollen with extra subcutaneous fluid water (edema). Initial studies show a serum albumin of 1.5 g/dL (normal for age 3.3-5.8) and total protein 2.7 g/dL (normal for age 5.3-8.1). Which of the following statements best explains the reason for the child’s edema?

a. Water forms strong covalent bonds with sodium salts

b. Proteins form hydrogen bonds with water and exert osmotic pressure to retain intravascular volume

c. Surface valine and isoleucine on proteins bind water and exert osmotic pressure

d. Surface glutamic and aspartic acid on proteins form hydrogen bonds with water and become impermeable to capillary walls

e. Surface hydroxyl groups due to protein serines and threonines form aggregates through hydrogen bonding with water and cannot pass capillary membranes

10. A 25-year-old African American female displays decreased appetite, increased urinary frequency, and thirst. Her physician suspects new-onset diabetes mellitus (MIM*222100) and confirms that she has elevated urine glucose and ketones. Which of the following blood values is most compatible with diabetic ketoacidosis?

11. A 2-year-old Caucasian girl presents with severe vomiting, dehydration, and fever. Initial blood studies show acidosis with a low bicarbonate and an anion gap (the sum of sodium plus potassium minus chloride plus bicarbonate is 40 and larger than the normal 12 ± 2). Preliminary results from the blood amino acid screen show two elevated amino acids, both with nonpolar side chains. A titration curve performed on one of the elevated species shows two ionizable groups with approximate pKs of 2 and 9.5. Which of the following pairs of elevated amino acids is most likely elevated?

a. Aspartic acid and glutamine

b. Glutamic acid and threonine

c. Histidine and valine

d. Leucine and isoleucine

e. Glutamine and isoleucine

12. Blood is drawn from a 21-year-old African American female with severe anemia and the globin protein is degraded for peptide and amino acid analysis. Of the results below, which change in globin primary structure is most likely to correlate with the clinical phenotype of anemia?

a. Ile-Leu-Val to Ile-Ile-Val

b. Leu-Glu-Ile to Leu-Val-Ile

c. Gly-Ile-Gly to Gly-Val-Gly

d. Gly-Asp-Gly to Gly-Glu-Gly

e. Val-Val-Val to Val-Leu-Val

13. A 35-year-old female with heavy menstrual periods (metrorrhagia) has anemia but does not respond to iron supplementation. Blood is drawn and the red cell hemoglobin is analyzed. Which of the following results is most likely if the patient has an altered hemoglobin molecule (hemoglobinopathy)?

a. Several proteins but only one red protein detected by high-performance liquid chromatography (HPLC)

b. Two proteins detected in normal amounts by Western blotting

c. Several proteins and two red proteins separated by native gel electrophoresis

d. Two labeled bands a slight distance apart after SDS-gel electrophoresis and reaction with labeled antibody to α- and β-globin

e. A reddish mixture of proteins retained within a dialysis membrane

14. A 2-year-old Caucasian girl is brought for evaluation after being found neglected in a trailer with no kitchen facilities. She has extreme irritability due to thin and bleeding gums with tender forearms and lower legs. A diagnosis of scurvy is made among other deficiencies and her vitamin C levels are low. Which of the following amino acids will be deficient in her bone proteins?

a. Hydroxytryptophan

b. Hydroxytyrosine

c. Hydroxyhistidine

d. Hydroxyalanine

e. Hydroxyproline

15. A newborn African American girl has a large and distorted cranium, short and deformed limbs, and very blue scleras (whites of the eyes). Radiographs demonstrate multiple limb fractures and suggest a diagnosis of osteogenesis imperfecta (brittle bone disease—MIM*155210). Analysis of type I collagen protein, a triple helix formed from two α₁-collagen and one α₂-collagen chains, shows a 50% reduction in the amount of type I collagen in the baby’s skin. DNA analysis demonstrates the presence of two normal α₁-alleles and one normal α₂-allele. These results are best explained by which of the following?

a. Deficiency of α₁-collagen peptide synthesis

b. Inability of α₁-chains to incorporate into triple helix

c. Defective α₁-chains that interrupt triple helix formation

d. Incorporation of defective α₂-chains that cause instability and degradation of the triple helix

e. A missense mutation that alters the synthesis of α₁-chains

16. A 12-year-old African American girl, who has tall stature, loose joints, and detached retinas, is found to have a mutation in type II collagen. Recall that collagen consists of a repeating tripeptide motif where the first amino acid of each tripeptide is the same. Which of the following amino acids is the recurring amino acid most likely to be altered in mutations that distort collagen molecules?

a. Glycine

b. Hydroxyproline

c. Hydroxylysine

d. Tyrosine

e. Tryptophan

17. Children with urea cycle disorders present with elevated serum ammonia and consequent neurologic symptoms including altered respiration, lethargy, and coma. Several amino acids are intermediates of the urea cycle, having side ammonia groups that join with free carbon dioxide and ammonia to produce net excretion of ammonia as urea (NH₂CONH₂). Which of the following amino acids has an ammonia group in its side chain and is thus likely to be an intermediate of the urea cycle?

a. Arginine

b. Aspartate

c. Methionine

d. Glutamate

e. Phenylalanine

18. A child who was normal at birth shows developmental delay with coarsened facial features and enlarged liver and spleen by age 1 year. He is suspected of having I-cell disease (inclusion-cell disease—MIM*252500), a lysosomal storage disease with progressive accumulation of complex carbohydrates and glycoproteins in organs. Affected individuals lack multiple enzymes in their lysosomes (with excess amounts in serum) because man-nose 6-phosphate groups that target enzymes to lysosomes are not correctly synthesized. Which of the following techniques for purification of proteins could be used to isolate the putative lysosomal membrane protein that recognizes mannose 6-phosphate groups and transports enzymes into lysosomes?

a. Dialysis

b. Affinity chromatography

c. Gel filtration chromatography

d. Ion exchange chromatography

e. Electrophoresis

19. An adolescent presents with shortness of breath during exercise and is found to be anemic. A hemoglobin electrophoresis is performed that is depicted in the figure below. The adolescent’s sample is run with controls including normal, sickle trait, and sickle cell anemia hemoglobin samples and serum. The adolescent is determined to have an unknown hemoglobinopathy. Which of the following lanes contains the adolescent’s sample?

a. Lane A

b. Lane B

c. Lane C

d. Lane D

e. Lane E

20. Which of the following proteolytic enzymes is activated by acid hydrolysis of the proenzyme form?

a. Carboxypeptidase

b. Chymotrypsin

c. Elastase

d. Pepsin

e. Trypsin

21. A 3-day-old African American female infant was normal at birth but becomes lethargic after several feedings; the medical student describes an unusual smell to the urine but is ignored. Infection (sepsis) is suspected, and blood tests show normal white blood cell counts with a serum pH of 7.0. Electrolytes reveal an anion gap, and evaluation for an inborn error of metabolism shows an abnormal amino acid screen. The report states that branched-chain amino acids are strikingly elevated. Which of the following amino acids does the report refer to?

a. Arginine

b. Aspartic acid

c. Isoleucine

d. Lysine

e. Glycine

22. In comparing the secondary structure of proteins, which of the following descriptions applies to both the α-helix and the β-pleated sheet?

a. All peptide bond components participate in hydrogen bonding.

b. N-terminals of chains are together and parallel.

c. The structure is composed of two or more segments of polypeptide chain.

d. N- and C-terminal ends of chains alternate in an antiparallel manner.

e. The chains are almost fully extended.

23. A 6-year-old African American girl with speech delay is found to have a large, abnormal peak when blood amino acids are measured. The abnormal amino acid migrates toward the anode, indicating a positively charged side group in addition to its carboxyl and amino groups. Which of the following amino acids is most probable and what medical procedure is most important?

a. Alanine; laryngoscopy

b. Glycine; hearing test

c. Histidine; hearing test

d. Leucine; laryngoscopy

e. Valine; hearing test

24. The oxygen carrier of muscle is the globular protein myoglobin. Which of the following amino acids is highly likely to be localized within the interior of the molecule?

a. Arginine

b. Aspartic acid

c. Glutamic acid

d. Valine

e. Lysine

25. A 2-year-old Asian child has stopped progressing in speech and develops coarse facial features with thick mucous drainage. Skeletal deformities including curved spine (kyphosis), thickened and short fingers, and curved limbs appear over the next year, and the child regresses to a vegetative state by age 10 years. The child’s urine tests positive for glycosaminoglycans that include which of the following molecules?

a. Collagen

b. γ-Aminobutyric acid

c. Heparan sulfate

d. Glycogen

e. Fibrillin

26. Under normal conditions in blood, which of the following amino acid residues of albumin is neutral?

a. Arginine

b. Aspartate

c. Glutamine

d. Glutamate

e. Histidine

27. A 20-year-old Caucasian female comes in with her husband for preconception counsel as they have decided to have children. Her gynecologist notices that she has very thin skin with multiple bruises and easy visualization of the underlying veins. Further history discloses joint hypermobility with frequent dislocation, and on physical examination she can appose her thumbs to her forearms, reach an arm behind her back to touch her umbilicus in front, and spontaneously dislocate her shoulder. Further referral and diagnostic DNA testing reveals that the woman has type IV Ehlers-Danlos syndrome (MIIM 130050) due to a mutation in the gene for type III collagen on chromosome 2. She is informed that a pregnancy would likely be lethal due to breakdown of major arteries from stress, and the couple decide to pursue adoption. Which of the statements below best apply to her collagen III gene mutation?

a. Mutation changing alanine to glycine in one type III collagen allele

b. Silent mutation in the codon for a lysine near the amino-terminus of one collagen allele

c. Mutation changing alanine to glycine in both collagen alleles

d. Mutation changing glycine to proline in one type III allele

e. Silent mutation in the codon for a lysine near the carboxy terminus of two collagen alleles

28. Which of the following amino acids is aromatic (ring compound), and in a pathway leading to neurotransmitters and melanin?

a. Arginine

b. Cystine

c. Glutamine

d. Leucine

e. Proline

f. Serine

g. Tyrosine

29. Which of the following substances is primarily found in tendons?

a. Collagen

b. Fibrillin

c. Fibrin

d. Fibronectin

e. Troponin

30. Which of the following is primarily found in the extracellular matrix?

a. Collagen

b. Fibrin

c. Keratin

d. Proteoglycan

e. Troponin

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