Which enzyme prevents aging?
**Core Concept**
Telomerase is a reverse transcriptase enzyme that adds nucleotides to the ends of telomeres, thus preventing telomere shortening and cellular aging. Telomeres are repetitive DNA sequences that cap the ends of chromosomes, protecting them from deterioration and fusion with neighboring chromosomes.
**Why the Correct Answer is Right**
Telomerase acts by adding nucleotides to the 3' end of telomeres, thereby maintaining or even lengthening telomeres. This prevents telomere shortening, which occurs due to the end-replication problem during DNA replication. Telomere shortening leads to cellular aging and ultimately apoptosis. Telomerase is highly expressed in embryonic stem cells, cancer cells, and germ cells, which are known for their high proliferative capacity.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because there is no widely recognized enzyme that prevents aging through a similar mechanism.
**Option B:** This option is incorrect because the enzyme responsible for DNA repair, DNA polymerase, does not directly prevent telomere shortening.
**Option C:** This option is incorrect because while sirtuins are a class of enzymes involved in aging, they do not directly prevent telomere shortening.
**Clinical Pearl / High-Yield Fact**
Telomere shortening is a hallmark of cellular aging, and telomerase activity is often used as a biomarker of cellular aging in various diseases, including cancer and aging-related disorders.
**Correct Answer: D. Telomerase. Telomerase is the enzyme that prevents aging by maintaining or lengthening telomeres.**