Correct Answer:
B. Protective caps at the end of chromosomes that shorten as cells divide.
Explanation:
The correct answer is Protective caps at the end of chromosomes that shorten as cells divide. because telomeres prevent DNA degradation, acting as a biological clock for aging cells.
- Step 1 (Structural Protection): Telomeres consist of repetitive, non-coding DNA sequences (TTAGGG) found at the tips of chromosomes, functioning like plastic aglets on shoelaces to keep genetic strands from unraveling or fusing.
- Step 2 (The Hayflick Limit): Due to the end-replication problem, telomeres shorten slightly with each round of cell division. When they become critically short, the cell hits its replication limit, triggering senescence or programmed death.
- Incorrect Options:
- A brain cell that stops functioning is incorrect because senescent neurons describe dying or degraded nervous system tissue, not a chromosome structure.
- A stomach enzyme that breaks down proteins is incorrect because protein-digesting enzymes in the stomach are classified as proteases, such as pepsin.
- A type of white blood cell is incorrect because immune defense cells traveling through the bloodstream are called leukocytes (such as lymphocytes or neutrophils).