DNA repair Practice Questions

Question 1

A 5-month-old male infant from a consanguineous marriage presents with severe sunburns and freckling in sun exposed areas. The mother explains that the infant experiences these sunburns every time the infant goes outside despite applying copious amounts of sunscreen. Which of the following DNA repair mechanisms is defective in this child?

Accepted Answer

Nucleotide excision repair

Answer

Non-homologous end joining

Answer

Homologous recombination

Answer

Base excision repair

Answer

Mismatch repair

Question 2

A 42-year-old woman presents to her primary care physician with fatigue. She reports that over the past 2 months, she has felt increasingly tired despite no changes in her diet or exercise. Her past medical history is notable for obesity, seasonal allergies, and hypertension. She takes ranitidine as needed and hydrochlorothiazide daily. Her family history is notable for colorectal cancer in her mother and maternal uncle, endometrial cancer in her maternal aunt, and ovarian cancer in her maternal grandmother. Her temperature is 98.8°F (37.1°C), blood pressure is 132/71 mmHg, pulse is 89/min, and respirations are 17/min. On exam, she has conjunctival pallor. A stool sample is hemoccult positive. A colonoscopy reveals a fungating hemorrhagic mass in the ascending colon. Which of the following processes is likely impaired in this patient?

Accepted Answer

Mismatch repair

Answer

Non-homologous end joining

Answer

Homologous recombination

Answer

Base excision repair

Answer

Nucleotide excision repair

Question 3

A 71-year-old man with colorectal cancer comes to the physician for follow-up examination after undergoing a sigmoid colectomy. The physician recommends adjuvant chemotherapy with an agent that results in single-stranded DNA breaks. This chemotherapeutic agent most likely has an effect on which of the following enzymes?

Accepted Answer

Topoisomerase I

Answer

DNA polymerase III

Answer

Helicase

Answer

Telomerase

Answer

Topoisomerase II

Question 4

A 34-year-old woman comes to the physician for evaluation of a breast lump she noticed 2 days ago while showering. She has no history of major illness. Her mother died of ovarian cancer at age 38, and her sister was diagnosed with breast cancer at age 33. Examination shows a 1.5-cm, nontender, mobile mass in the upper outer quadrant of the left breast. Mammography shows pleomorphic calcifications. Biopsy of the mass shows invasive ductal carcinoma. The underlying cause of this patient's condition is most likely a mutation of a gene involved in which of the following cellular events?

Accepted Answer

Repair of double-stranded DNA breaks

Answer

Inhibition of programmed cell death

Answer

Regulation of intercellular adhesion

Answer

Activity of cytoplasmic tyrosine kinase

Answer

Arrest of cell cycle in G1 phase

Question 5

A 5-year-old girl is brought to the physician by her mother because of a 1-month history of a painful ulcer on her face. She has developed painful sunburns in the past with minimal UV exposure. Examination of the skin shows a 2-cm ulcerated nodule on the left cheek. There are scaly, hyperpigmented papules and plaques over the skin of the entire body. Ophthalmologic examination shows decreased visual acuity, clouded corneas, and limbal injection. Examination of a biopsy specimen from the facial lesion shows poorly-differentiated squamous cell carcinoma. Impairment of which of the following proteins is the most likely cause of this patient's condition?

Accepted Answer

Excision endonuclease

Answer

Rb nuclear protein

Answer

Base-specific glycosylase

Answer

ATM serine/threonine kinase

Answer

DNA helicase

Question 6

A 19-year-old woman presents to the physician for a routine health maintenance examination. She has a past medical history of gastroesophageal reflux disease. She recently moved to a new city to begin her undergraduate studies. Her father was diagnosed with colon cancer at age 46. Her father's brother died because of small bowel cancer. Her paternal grandfather died because of stomach cancer. She takes a vitamin supplement. Current medications include esomeprazole and a multivitamin. She smoked 1 pack of cigarettes daily for 3 years but quit 2 years ago. She drinks 1–2 alcoholic beverages on the weekends. She appears healthy. Vital signs are within normal limits. Physical examination shows no abnormalities. Colonoscopy is unremarkable. Germline testing via DNA sequencing in this patient shows mutations in DNA repair genes MLH1 and MSH2. Which of the following will this patient most likely require at some point in her life?

Accepted Answer

Annual colonoscopy beginning at 20–25 years of age

Answer

Celecoxib or sulindac therapy

Answer

Surgical removal of a desmoid tumor

Answer

Prophylactic proctocolectomy with ileoanal anastomosis

Answer

Measurement of carcinoembryonic antigen and CA 19-9 yearly

Question 7

A 7-month-old boy presents to the family physician with extensive scaliness and pigmentation of sun-exposed skin areas. His mother says that these symptoms were absent until mid-spring and then became significantly worse after their trip to California in the summer. The child was born in December to a consanguineous couple after an uncomplicated pregnancy. He is breastfed and receives mashed potatoes, bananas, and carrots as complementary foods. His weight is 8.5 kg (18.7 lb) and length is 70 cm (2 ft 96 in). The patient’s vital signs are within normal limits for his age. On physical examination, there is freckling, scaling, and erythema on the sunlight-exposed areas of the face, trunk, and upper and lower extremities. No blistering, scarring, hypertrichosis, or alopecia is noted. The rest of the exam is unremarkable. Which process is most likely disrupted in this patient?

Accepted Answer

Nucleotide-excision DNA repair

Answer

Base-excision DNA repair

Answer

Hydroxylation of proline and lysine in the procollagen molecule

Answer

Conversion of uroporphyrinogen III to coproporphyrinogen III

Answer

NAD production

Question 8

As part of a clinical research study, the characteristics of neoplastic and normal cells are being analyzed in culture. It is observed that neoplastic cell division is aided by an enzyme which repairs progressive chromosomal shortening, which is not the case in normal cells. Due to the lack of chromosomal shortening, these neoplastic cells divide more rapidly than the normal cells. Which of the following enzymes is most likely involved?

Accepted Answer

Telomerase

Answer

Topoisomerase

Answer

DNA polymerase

Answer

Reverse transcriptase

Answer

Protein kinase

Question 9

A 28-year-old woman, gravida 1, para 0, at 20 weeks' gestation comes to the physician for genetic counseling. Her brother and maternal uncle both have anemia that worsens after taking certain medications. Based on the pedigree shown, what is the probability that her son will be affected by the disease?

Accepted Answer

25%

Answer

12.5%

Answer

100%

Answer

50%

Answer

0%

Question 10

An 11-year-old boy is brought to the emergency room with acute abdominal pain and hematuria. Past medical history is significant for malaria. On physical examination, he has jaundice and a generalized pallor. His hemoglobin is 5 g/dL, and his peripheral blood smear reveals fragmented RBC, microspherocytes, and eccentrocytes (bite cells). Which of the following reactions catalyzed by the enzyme is most likely deficient in this patient?

Accepted Answer

D-glucose-6-phosphate + NADP+ → 6-phospho-D-glucono-1,5-lactone + NADPH + H+

Answer

Glucose-1-phosphate + UTP → UDP-glucose + pyrophosphate

Answer

Glucose + ATP → Glucose-6-phosphate + ADP + H+

Answer

D-glucose 6-phosphate → D-fructose-6-phosphate

Answer

Glucose-6-phosphate + H2O → glucose + Pi

DNA repair

Study Resources

Lessons

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Lessons

Types of DNA damage

Base excision repair

Nucleotide excision repair

Mismatch repair

Double-strand break repair

Homologous recombination

Non-homologous end joining

Direct repair mechanisms

DNA damage response signaling

DNA repair deficiency syndromes

Cancer susceptibility and DNA repair

Aging and DNA repair

Practice Questions

Flashcards

About DNA repair for USMLE

Lessons in DNA repair

Master DNA repair