3. One hallmark of cancer cells is their ability to divide indefinitely, in contrast with most normal somatic cells that undergo senescence after 30 to 50 generations of divisions. One reason for this...

Extracted text: 3. One hallmark of cancer cells is their ability to divide indefinitely, in contrast with most normal somatic cells that undergo senescence after 30 to 50 generations of divisions. One reason for this difference is that many cancer cells express the Telomerase enzyme that can mediate telomere lengthening. Interestingly, about 15% of tumors do not express telomerase. Instead, they lengthen their telomeres by an alternative pathway. Tumor cells of this class appear to have telomeres that are highly heterogenous in length; some telomeres have many more TTAGGG repeats than others. a. Diagram an event involving homologous recombination that would allow some telomeres in these cells to become longer. What feature(s) of telomeres make(s) such homologous recombination possible? b. Does this recombination need to occur between homologous telomeres (that is, telomeres of the same arm of the same chromosome)? If such recombination could occur between nonhomologous telomeres, how might you detect it? c. Almost all cells that undergo this alternative telomere lengthening pathway have 1-eircles: small molecules of circular DNA made up almost exclusively of telomeric sequences Diagram how these circles might participate in telomere lengthening.