Final answer:
Telomerase extends the 3' end of chromosomes using its RNA component as a template to prevent chromosome shortening. DNA polymerase fills in the complementary strand. Telomerase is active in germ and stem cells, and its discovery won a Nobel Prize.
Step-by-step explanation:
How Telomerase Works
Telomerase is an enzyme crucial for maintaining the length of telomeres, which are the repeating DNA sequences at the ends of chromosomes. The catalytic part of telomerase, along with its built-in RNA component, known as TERC, works by adding nucleotides to the 3' end of the DNA strand in a 5' to 3' direction. The RNA serves as a template for new DNA synthesis. Once the 3' end of the lagging strand template is sufficiently elongated, DNA polymerase can then fill in the complementary strand using the usual base-pairing rules.
Telomerase is particularly active in germ cells and adult stem cells, allowing these cells to divide repeatedly without losing important genetic information from the chromosome ends. This activity contrasts with adult somatic cells, where telomerase is usually inactive, contributing to cellular aging. Additionally, telomerase is found in some cancer cells, which helps them to proliferate unchecked. Elizabeth Blackburn, Carol W. Greider, and Jack W. Szostak were awarded the Nobel Prize for their discovery of telomerase and its role in chromosome protection.