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.

#Question id: 1497

#Unit 4. Cell Communication and Cell Signaling

In children with retinoblastoma, the chromosomal deletion that is present in all of their cells indicates that the chromosomal aberration:

#Question id: 1498

#Unit 4. Cell Communication and Cell Signaling

Would you expect to find that the cells of children with nonfamilial (i.e., sporadic) retinoblastoma have the chromosomal deletion referred to in number (9) above?

#Question id: 1499

#Unit 4. Cell Communication and Cell Signaling

The normal protein product of the RB gene acts as an:

#Question id: 1500

#Unit 4. Cell Communication and Cell Signaling

Which of the following is not a normal function of p53?

#Question id: 1501

#Unit 4. Cell Communication and Cell Signaling

When a culture of rodent cells is infected with a DNA tumor virus whose gene products bind to p53 and RB, all the cells take on characteristics of malignancy. If the viral gene coding the p53-binding protein is mutated, but that coding for the RB-binding protein is not mutated, how will infected cells respond?

#Question id: 1502

#Unit 4. Cell Communication and Cell Signaling

The textbook states that cells of patients with adenomatous polyposis coli (APC) “contain a deletion of a small portion of chromosome #5, which was subsequently identified as the site of a tumor-suppressor gene called APC.” In which cells of these patients would you expect to find this chromosomal deletion?