Question

What is the enzyme by which cancer cells become immortalised?

• A. DNA polymerase
• B. mRNA polymerase
• C. Telomerase
• D. Topoisomerase

Hint:

Telomerase rebuilds shortened telomeres, letting cancer cells bypass the normal division limit.

Answer 1

The Correct Option is C

Cell immortalisation is about beating the natural limit on how many times a cell can divide, and that limit is set by the telomeres at the chromosome ends.

1. DNA polymerase: Copies the DNA strand during replication, but it cannot fully replicate the very end of a linear chromosome, which is exactly why telomeres shorten over successive divisions.
2. mRNA polymerase: Transcribes DNA into messenger RNA. It has no part in copying or lengthening telomeres.
3. Telomerase: Carries its own RNA template and extends the telomere repeats after each round of division. Cancer cells reactivate this enzyme, which is normally switched off in most adult tissues, so their telomeres stop shrinking and the cells can divide without limit.
4. Topoisomerase: Cuts and reseals DNA strands to relieve supercoiling ahead of the replication fork. It does not touch telomere length.

Because telomerase is the enzyme that keeps telomeres from wearing down, its reactivation is what gives cancer cells their immortal, endlessly dividing behaviour.

Let's summarize:

• Telomere shortening normally caps how many times a cell can divide.
• Telomerase reactivation in cancer cells removes this cap.

The correct enzyme is telomerase.