Telomerase

Telomerase, also called terminal transferase, is a special kind of ribonucleoprotein that helps keep our cells healthy. It adds a specific telomere repeat sequence to the ends of telomeres, which are protective caps on the tips of chromosomes. These telomeres guard the chromosome ends from damage or sticking together with nearby chromosomes.

Telomerase works as a reverse transcriptase enzyme, carrying its own RNA molecule to use as a pattern while it lengthens the telomeres. It is especially active in gametes, the cells that become eggs or sperm, and in many cancer cells. However, in most regular body cells, called somatic cells, telomerase is usually not present. This enzyme plays an important role in how cells age and stay healthy.

History

The idea that telomeres might help with aging was first suggested in 1973 by a scientist named Alexey Olovnikov. In 1984, Carol W. Greider and Elizabeth Blackburn discovered telomerase in a tiny organism called a ciliate. For this work, they later won a Nobel Prize in Physiology or Medicine together with Jack W. Szostak. Scientists have since learned more about how telomerase works in both simple organisms and humans, helping us understand its role in cell aging and cancer.

Structure

The main part of telomerase is a protein called telomerase reverse transcriptase, which helps add DNA sequences to the ends of chromosomes. This protein is shaped like a right hand and works similarly to enzymes found in viruses and bacteria.

The full telomerase complex includes telomerase RNA, the telomerase reverse transcriptase protein, and several other helper molecules. These work together to protect chromosome ends. In humans, the complex also includes special proteins that bind to the RNA and help the enzyme function properly.

Mechanism

The protein TPP1 helps bring the telomerase enzyme to the ends of chromosomes, called telomeres. Telomerase uses a piece called TERC to add a special six-nucleotide sequence to the end of chromosomes. In animals, this sequence is TTAGGG.

Telomerase works by matching part of the template to the end of the chromosome, adding a new repeat, then moving to add more repeats. This helps stop the telomeres from getting shorter.

Clinical implications

Telomerase helps restore tiny bits of DNA called telomeres, which get shorter each time a cell divides. Normally, when telomeres get too short, cells stop dividing. But telomerase lets cells keep dividing by adding back these bits of DNA. This ability to divide forever is common in cancer cells, which helps them grow uncontrollably.

Embryonic stem cells, which develop into babies, have a lot of telomerase. In adults, only certain cells like sperm cells and some immune cells make telomerase. Most regular body cells don’t make much telomerase. Studies show that telomere length doesn’t always match an animal’s lifespan, and in some tissues like brain and muscle, telomeres don’t shorten much with age. Some researchers think telomerase might help fight aging, but it can also increase cancer risk. There are products on the market claiming to boost telomerase to delay aging, but their effects aren’t fully proven.

Certain rare diseases, like Werner syndrome and Progeria syndrome, are linked to shorter telomeres. These conditions may come from problems with DNA repair rather than telomere length itself. In cancer, cells often activate telomerase to avoid dying when telomeres get too short. This helps cancer cells live longer and grow into tumors. Scientists are studying ways to block telomerase to treat cancer, and some treatments aim to weaken cancer cells by stopping telomerase activity.

TERT Splice Variants

Telomerase has different forms, called splice variants, which come from the same gene but are put together in slightly different ways. These variants can affect how well telomerase works and might play roles in both normal cell growth and in diseases like cancer. Scientists study these variants to understand better how cells stay healthy and how they sometimes go wrong.