Correct option is D
Telomeres are protective caps at the ends of eukaryotic chromosomes that prevent chromosome degradation and fusion. Telomerase, an enzyme that extends telomeres, is crucial for maintaining genomic stability, particularly in stem cells and cancer cells.
Evaluating the Statements
Statement A: "Telomere-binding proteins (TBPs) are believed to shield telomeres from the cell’s DNA repair machinery, preventing them from being recognized as double-strand breaks."
- Correct.
- Telomeres are coated with shelterin proteins (a type of TBP), which protect the ends of chromosomes.
- This prevents DNA repair mechanisms from mistaking telomeres for double-strand breaks, avoiding unnecessary repair and chromosomal fusion.
Statement B: "Telomeres in human cells are repeats of TTAGGG sequence that can extend up to 150 kb, which are replicated by the action of TERT in actively dividing cells."
- Incorrect.
- Human telomeres consist of TTAGGG repeats, but they typically range from 5-15 kb, not 150 kb.
- TERT (Telomerase Reverse Transcriptase) extends telomeres but does not replicate them to such an extreme length.
Statement C: "In differentiated cells, telomerase is inactive, leading to shortening of telomeres over hundreds of cell divisions, damage to ends of chromosomes, and eventually apoptosis."
- Correct.
- Most somatic cells lack active telomerase, causing progressive telomere shortening with each cell division.
- This contributes to cellular aging, genomic instability, and programmed cell death (apoptosis).
Statement D: "The persistence of telomerase activity in several cancers allows the cells to continue to proliferate."
- Correct.
- Many cancer cells reactivate telomerase, allowing indefinite replication by preventing telomere shortening.
- This is a hallmark of cancer cell immortality.
Correct Answer:
- A, C, and D are correct.
- Option 4 (A, C, and D).
