With respect to the DNA methylation mechanism in mammalian cells, which of the following statements, if any, is true? 

I. The principal role of the DNMT1 DNA methyltransferase is in de novo methylation. 

II. The DNMT3A and DNMT3B DNA methyltransferases require hemi-methylated DNA as a substrate and are responsible for methylating nascent DNA strands that are complementary to methylated parental DNA strands.

III. Active DNA demethylation means removal of methyl groups from a hemi-methylated DNA double helix. 

IV. DNA methylation is not essential in mammalian development.

TLS Online TPP Program

#Question id: 12269

#Unit 7. System Physiology – Animal

If a woman hears her baby cry, she may experience milk ejection from the nipples even before the baby is placed to the breast. What is the explanation for this?

TLS Online TPP Program

#Question id: 12270

#Unit 7. System Physiology – Animal

Which of the following hormones is not stored in its endocrine-producing gland?

TLS Online TPP Program

#Question id: 12271

#Unit 7. System Physiology – Animal

A young woman comes to the emergency room with a vertebral compression fracture. Radiographs of the spine indicate generalized demineralization. She is vegetarian, does not smoke or drink alcohol, has normal plasma potassium concentration of 5.4 mEq/L, sodium concentration of 136 mEq/L, plasma calcium concentration is 7.0 mg/dL. Her vitamin D3 value is several times greater than normal, although her 1,25-dihydroxycholecalciferol concentration is at the lower limit of detectability. She has been in renal failure for the last 5 years and undergoes hemodialysis three times each week. What is the cause of her low 1,25-dihydroxycholecalciferol level?

TLS Online TPP Program

#Question id: 12272

#Unit 7. System Physiology – Animal

A neonate develops a jaundice condition with a bilirubin concentration of 10 mg/dL on day 2 (normal is 3 mg/dL at 2 days old). The neonatologist can be confident that the condition is not erythroblastosis fetalis if which of the following is true?

TLS Online TPP Program

#Question id: 12273

#Unit 7. System Physiology – Animal

Which of the following findings would likely be reported in a patient with a deficiency in iodine intake?

TLS Online TPP Program

#Question id: 12274

#Unit 7. System Physiology – Animal

Before intercourse, a woman irrigates her vagina with a solution that lowers the pH of the vaginal fluid to 4.5. What will be the effect on sperm cells in the vagina?