Initiation of transcription — MCQs

A 45-year-old man presents with a hereditary condition affecting iron metabolism. The condition is caused by mutations in a gene that normally stimulates hepatic production of hepcidin, a hormone that downregulates iron absorption by inhibiting ferroportin (an iron transporter) on enterocytes. Due to this genetic defect, the patient has developed iron overload. He presents with skin hyperpigmentation, fatigue, joint pain, and diabetes mellitus. Laboratory studies show elevated serum ferritin and transferrin saturation. The patient is also developing early signs of cardiovascular complications from iron deposition. What would be the first cardiac manifestation in this patient?

Researchers are investigating oncogenes, specifically the KRAS gene that is associated with colon, lung, and pancreatic cancer. They have established that the gain-of-function mutation in this gene increases the chance of cancer development. They are also working to advance the research further to study tumor suppressor genes. Which of the genes below is considered a tumor suppressor gene?

A 25-year-old male is brought to the emergency department by his friends after a camping trip. He and his friends were in the woods camping when the patient started experiencing severe right upper quadrant abdominal pain after foraging and ingesting some wild mushrooms about 3 hours earlier. The patient is lethargic on exam and appears jaundiced. He has scleral icterus and is severely tender to palpation in the right upper quadrant. He has scattered petechiae on his extremities. Liver function tests are: Serum: Na+: 134 mEq/L Cl-: 100 mEq/L K+: 4.2 mEq/L HCO3-: 24 mEq/L Urea nitrogen: 50 mg/dL Glucose: 100 mg/dL Creatinine: 1.4 mg/dL Alkaline phosphatase: 400 U/L Aspartate aminotransferase (AST, GOT): 3278 U/L Alanine aminotransferase (ALT, GPT): 3045 U/L gamma-Glutamyltransferase (GGT): 100 U/L The most likely cause of this patient’s clinical presentation acts by inhibiting which of the following molecules?

E. coli has the ability to regulate its enzymes to break down various sources of energy when available. It prevents waste by the use of the lac operon, which encodes a polycistronic transcript. At a low concentration of glucose and absence of lactose, which of the following occurs?

A 55-year-old man, who was recently diagnosed with tuberculosis, presents to his primary care provider as part of his routine follow-up visit every month. He is currently in the initial phase of anti-tubercular therapy. His personal and medical histories are relevant for multiple trips to Southeast Asia as part of volunteer activities and diabetes of 5 years duration, respectively. A physical examination is unremarkable except for a visual abnormality on a color chart; he is unable to differentiate red from green. The physician suspects the visual irregularity as a sign of toxicity due to one of the drugs in the treatment regimen. Which of the following is the mechanism by which this medication acts in the treatment of Mycobacterium tuberculosis?

A 37-year-old man previously treated with monotherapy for latent tuberculosis develops new-onset cough, night sweats and fever. He produces a sputum sample that is positive for acid-fast bacilli. Resistance testing of his isolated bacteria finds a mutation in the DNA-dependent RNA polymerase. To which of the following antibiotics might this patient's infection be resistant?

Although nucleotide addition during DNA replication in prokaryotes proceeds approximately 20-times faster than in eukaryotes, why can much larger amounts of DNA be replicated in eukaryotes in a time-effective manner?

You are culturing bacteria on lactose-rich and glucose-free media. These bacteria regulate gene expression via the lac operon to ferment lactose into glucose and galactose for their metabolic needs. You add free glucose to the media. The addition of glucose reduces lactose fermentation secondary to which of the following changes?

An investigator is studying the genotypes of wingless fruit flies using full exome sequencing. Compared to wild-type winged fruit flies, the wingless fruit flies are found to have a point mutation in the gene encoding wing bud formation during embryogenesis. The point mutation in the gene causes the mRNA transcript to have a 'UUG' segment instead of an 'AUG' segment. Which of the following processes is most likely affected by this mutation?

A 82-year-old woman is brought to the emergency department from a retirement community after she was found down during the evening. On presentation, she complains that she experienced several hours of nausea, vomiting, crampy abdominal pain, and diarrhea prior to blacking out. She said that she cannot recall any factors that may have triggered her symptoms; however, she recalls that some of her friends with whom she eats also had similar symptoms earlier in the day and were brought to the hospital. They often go for walks and occasionally cook for themselves from a garden that they keep in the woods behind the facility. One of the residents on the team recalls seeing other patients from this facility earlier today, one of whom presented with kidney failure and scleral icterus prior to passing away. The enzyme most likely affected in this case has which of the following functions?