Quiz- Molecular Biochemistry 1
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Question 1 of 26
1. Question
A 4-year-old boy is brought to the physician for fatigue and persistent bone pain. Physical examination shows diffuse lymphadenopathy and multiple purpura over his arms and legs. Laboratory analysis reveals anemia and thrombocytopenia, and a peripheral blood smear shows lymphoblasts. After further workup, he is diagnosed with acute lymphoblastic leukemia and started on a chemotherapy regimen that includes doxorubicin. This agent intercalates between DNA base pairs and inhibits DNA replication, a process that normally occurs at sites known as replication forks. As the replication forks move across the DNA molecule, 2 distinct daughter strands are formed. Which of the following is unique to the daughter strand that is synthesized in the opposite direction of the growing replication fork?
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Question 2 of 26
2. Question
In an experiment, erythrocyte precursor cells are incubated in a medium containing radiolabeled cysteine. These radiolabeled cysteine residues are attached to their appropriate tRNAs by the enzyme aminoacyl-tRNA synthetase. The bound cysteine residues are then chemically modified to form alanine. The end product of this reaction is a tRNA molecule that contains the cysteine anticodon but is mischarged with alanine. Which of the following is most likely to occur to this alanine residue during polypeptide synthesis of alpha-hemoglobin?
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Question 3 of 26
3. Question
A geneticist is performing an experiment to alter protein structures by incorporating modified amino acids into their polypeptide sequences. During the process, she incubates dermal fibroblasts in a medium containing fluorescently labeled lysine residues. After several hours, she finds that aminoacyl tRNA synthetase in the fibroblasts “loads” lysine residues onto tRNA molecules containing the anticodon UUU. This residue most likely attaches to tRNA at which of the following sites in the image shown below?
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Question 4 of 26
4. Question
A 32-year-old man is recovering from extensive burns. Fibroblasts near the site of injury actively synthesize precursor mRNA to be used as templates for protein synthesis. After transcription, extensive processing of the precursor RNA occurs to form the finalized mRNA sequence. The finalized mRNA then exits the nucleus and undergoes translation by ribosome complexes before being degraded. Which of the following steps involving the processing and handling of mRNA occurs only within the cytoplasm of cells?
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Question 5 of 26
5. Question
A 34-year-old man develops severe chest and abdominal pain while shopping in a mall. Paramedics arrive and find him in severe distress. Several minutes later, he suffers a cardiac arrest with pulseless electrical activity and cannot be resuscitated. Postmortem examination reveals an internal hemorrhage as the cause of death. Histochemical evaluation of the patient’s tissues reveals a defect affecting a large extracellular glycoprotein. This protein is normally found abundantly in large blood vessels, periosteum, and zonular fibers of the lens and functions to form microfibrils by surrounding elastin. This patient most likely suffered from which of the following conditions?
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Question 6 of 26
6. Question
A researcher develops 2 functional mRNA sequences composed of CUC and CUU trinucleotide repeats, respectively. He subsequently incubates these mRNAs in a solution containing functional ribosomes and tRNAs charged with the appropriate amino acids. After several hours, it is found that both mRNA sequences produce polypeptide chains containing leucine repeats. This observed finding is due to which of the following genetic principles?
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Question 7 of 26
7. Question
Molecular biologists undertake a series of experiments designed to classify proteins involved in various intracellular signaling pathways. During one of the experiments, a protein mixture obtained from a cell culture is separated by gel electrophoresis and subsequently transferred to a filter membrane. Labeled double-stranded DNA probes are then used to detect a specific protein of interest in the sample. Which of the following proteins is most likely to be detected by this method?
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Question 8 of 26
8. Question
A dermatology researcher is studying the role of different amino acids in wound healing. She cultures mature dermal fibroblasts in growth media. After several days, the fibroblasts begin synthesizing polypeptide chains that assemble into triple helical structures, followed by fibrils. The fibrillar proteins are hydrolyzed and separated into their constituent amino acids via paper chromatography. Which of the following amino acids is most likely to be found in highest quantity in these proteins?
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Question 9 of 26
9. Question
A 6-month-old boy is evaluated in the clinic due to delayed motor development. The mother reports that the boy is weaker than other children his age. He can barely lift his head up when prone and is unable to roll to the side. Physical examination shows generalized hypotonia and decreased deep tendon reflexes. Further evaluation reveals mutation of a protein involved in the assembly of small nuclear ribonucleoproteins (snRNPs) in motor neurons. This patient most likely has impaired function of which of the following cellular elements?
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Question 10 of 26
10. Question
A genetic researcher is comparing the DNA replication process of prokaryotic and eukaryotic cells. In an experiment, Escherichia coli and human cells are cultured in separate media containing tagged nucleotides and their rates of DNA replication are determined. Although the eukaryotic genome is significantly larger and more complex than that of the prokaryote, eukaryotic DNA replication still occurs in a timely manner. Which of the following features of eukaryotic replication best explains this observation?
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Question 11 of 26
11. Question
A 24-year-old woman comes to the office due to a persistent facial rash. The patient easily develops “sunburns” after sun exposure and her fingers “turn blue” in cold weather. She has also felt more fatigued than usual. Physical examination shows a facial rash in a butterfly distribution that spares the nasolabial folds. Laboratory studies reveal several types of autoantibodies directed against components of the cell nucleus. One specific antibody targets proteins complexed with small nuclear ribonucleic acid. These protein-ribonucleic acid complexes are most likely involved in which of the following cellular functions?
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Question 12 of 26
12. Question
A 2-year-old boy is being evaluated at the office for failure to thrive and developmental delay. Medical history is significant for recurrent ear infections since 6 months of age. Physical examination shows corneal clouding, hepatosplenomegaly, and restricted joint mobility. Further evaluation shows deficient phosphorylation of mannose residues on certain glycoproteins in the Golgi apparatus. In unaffected patients, these proteins are normally transported to which of the following cellular locations?
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Question 13 of 26
13. Question
A 24-year-old man comes to emergency department complaining of abdominal pain, vomiting, and severe watery diarrhea. He recently returned from a camping trip and admits to eating wild mushrooms that he collected in the woods. His past medical history is insignificant and he takes no medications. He does not use illicit drugs. On physical examination, he is ill-appearing and jaundiced. His liver edge is soft, tender, and palpable 4 cm below the right costal margin. Laboratory tests are significant for elevated levels of alanine aminotransferase, aspartate aminotransferase, and bilirubin. Synthesis of which of the following is most likely to be directly inhibited by the responsible toxin?
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Question 14 of 26
14. Question
A pharmaceutical researcher develops a novel antibacterial drug that works by inhibiting exonuclease activity during DNA replication. When actively dividing Escherichia coli is exposed to the drug, enzyme-mediated nucleotide removal in the 5′ to 3′ direction is impaired, leading to inhibition of bacterial growth. Which of the following enzymes is the most likely target of this drug?
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Question 15 of 26
15. Question
A 42-year-old woman comes to the neurologist for enrollment in a research study. She has a 15-year history of resting tremor, bradykinesia, and cogwheel rigidity consistent with Parkinson’s disease. One of her siblings recently started having similar symptoms. Genetic analysis is performed on the patient and her affected sibling. The results show a loss-of-function mutation in a gene that leads to an accumulation of misfolded proteins. Which of the following biochemical processes is most likely defective in this patient?
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Question 16 of 26
16. Question
A 65-year-old woman with chronic obstructive pulmonary disease and type II diabetes mellitus comes to the emergency department due to profound fevers and malaise. After initial evaluation, she is hospitalized for septicemia. Blood cultures plated on lactose-containing media grow rapidly dividing gram-negative bacteria. Replication of these microbial cells requires synthesis of two daughter strands of DNA using the parent strands as templates. Which of the following processes will differ the most between the 2 daughter strands formed at each replication fork?
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Question 17 of 26
17. Question
A 47-year-old woman has a tumor that is causing symptoms of excessive hormone production. Surgical resection of the lesion is performed with no operative complications, and the neoplastic tissue is subjected to detailed pathologic studies. Electron microscopy reveals the tumor cells have highly developed, smooth endoplasmic reticulum. Which of the following is a possible direct effect of the substance secreted by these cells?
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Question 18 of 26
18. Question
A 44-year-old man is evaluated due to progressive dyspnea over the past several years. The patient has no associated chest pain or palpitations. Physical examination shows a prolonged expiratory phase without wheezes or rhonchi. CT scan of the chest demonstrates bilateral lower lobe–predominant emphysema. Further testing reveals that the patient has a protease inhibitor deficiency, which has led to increased elastin fiber breakdown. Elastin fibers within alveolar walls normally allow the lung to stretch during active inspiration and recoil during passive expiration. Which of the following most likely contributes to this property of elastin?
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Question 19 of 26
19. Question
Microbiologists are investigating sugar metabolism in wild-type and mutant strains of Escherichia coli. Both strains are found to grow viable colonies on lactose-containing media. Each strain is then cultured on a new growth medium containing only glucose. Representative colonies of each strain from the new media undergo Western blot processing using a fluorescently labeled probe specific for β-galactosidase. Wild-type bacterial colonies are found to contain only trace quantities of β-galactosidase. However, the mutant colonies express significant amounts of β-galactosidase. Further analysis reveals that the variant strain contains a mutation that inhibits the binding of a certain protein to its regulatory sequence. In which of the following locations did this mutation most likely occur?
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Question 20 of 26
20. Question
A 2-year-old boy is evaluated for easy bruising. His parents report that he develops marked bruising and open wounds following minor trauma. The skin is difficult to suture due to its extreme fragility. Physical examination reveals hyperextensible skin, multiple ecchymoses over the forearms and pretibial regions, and an umbilical hernia. A skin biopsy is performed, and histochemical evaluation of the biopsy reveals a defect in extracellular processing of collagen. Which of the following steps of collagen synthesis is most likely impaired in this patient?
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Question 21 of 26
21. Question
A 56-year-old man comes to the office due to difficulty swallowing for the past several months. He has the most trouble with solid foods and says, “They seem to get stuck in my throat if I don’t chew a lot.” The patient has no chest pain or heartburn and has lost 4.5 kg (10 lb) in the last 3 months. He has been an avid hunter for many years and frequently cures the meat he eats with sodium nitrite. Physical examination is unremarkable. Endoscopy shows an ulcerated mass in the distal third of the esophagus, and biopsy samples are obtained from the mass and adjacent normal mucosa. Analysis of the samples shows accelerated cytosine deamination of chromosomal DNA in both normal and malignant epithelial cells. This damage is most likely to be repaired through which of the following enzymatic sequences?
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Question 22 of 26
22. Question
A 34-year-old woman comes to the physician with abdominal pain and melena. She also complains of progressive fatigue and a 5 kg (11 lb) weight loss over the last 2 months. She has a strong family history of colon, endometrial, and ovarian cancer. Colonoscopy shows a protuberant, friable mass in the ascending colon, and biopsy is diagnostic for colon adenocarcinoma. Genetic analysis confirms a mutation consistent with Lynch syndrome (hereditary nonpolyposis colon cancer). Which of the following is most likely responsible for the development of colon cancer in this patient?
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Question 23 of 26
23. Question
A series of experiments is being conducted to determine the structure and function of different types of bacterial RNA. Cultures of Staphylococcus aureus are exposed to chemicals that lyse the bacterial cells, and the RNA molecules are then extracted. A specific RNA consisting of 90 nucleotides is purified for further analysis. It is found to contain high amounts of chemically modified bases such as dihydrouridine, pseudouridine, and ribothymidine, and its secondary structure arises from base pairing within the chain. Which of the following is the most likely composition of the 3′-end of this molecule?
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Question 24 of 26
24. Question
An 18-year-old woman comes to the office for evaluation of graying hair. The patient has no other concerns and has otherwise been healthy. She reports that her mother had similar features at a young age and died of progressive pulmonary fibrosis. Examination shows diffuse gray hair. There are white patches on the surface of the tongue. Cardiopulmonary examination is unremarkable, and the abdomen is soft and nondistended. Skin examination shows areas of reticular hyperpigmentation on the neck and torso. The nails of the fingers and toes appear thin. Genetic testing reveals a loss-of-function mutation affecting the telomerase reverse transcriptase gene. Which of the following cell types is most likely to be affected by this mutation?
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Question 25 of 26
25. Question
A 9-month-old boy is brought to the clinic for a routine follow-up. His mother is concerned because the patient is not yet able to sit up unsupported. He was born at term and has had muscle weakness since birth. Vital signs are normal. The patient is alert but has diminished tone. Examination shows a prominent forehead with a depressed nasal bridge. Eye examination shows epicanthal folds. Analysis of lysosomal acid hydrolases shows an increased concentration within the serum and a decreased level within the cultured skin fibroblast cells. This patient most likely has a defect in which of the following steps of enzyme production?
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Question 26 of 26
26. Question
A 58-year-old man comes to the office with a persistent dry cough. He also has involuntarily lost 10 kg (22 lb) over the past 3 months. The patient drinks 2 or 3 beers daily and has a 40-pack-year smoking history. Physical examination shows dullness to percussion over the right lower lung base. CT scan of the chest reveals a right-sided pleural effusion and a mass in the lower lobe of the right lung. Microscopic examination of the mass demonstrates malignant cells with large nuclei that contain prominent, round, basophilic bodies, as shown in the image below:
Which of the following enzymes is most likely to function only within this basophilic region of the nucleus?
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