Telomerase

  • CAS Number: 9068-38-6

Telomerase is an enzyme of the cell nucleus, which is composed of a protein ( TERT ) and one long RNA portion (TR). This enzyme represents the end pieces of the chromosomes, the telomeres so-called restore. The enzyme activity of telomerase can be determined by the TRAP method.

Discovery

Telomerase was discovered in 1985 by the two researchers Elizabeth Blackburn and Carol Greider in the ciliate Tetrahymena. They were for it awarded the 2009 Paul Ehrlich Prize and, along with Jack W. Szostak, the Nobel Prize in Physiology or Medicine.

Features

The enzyme is a reverse transcriptase, which uses the RNA component as a template. Reverse transcriptases are likely to date from the ancient RNA world and are the only constant in all retroelements. It is believed today that they are of retroviral origin.

Function

The length of telomeres is different for different species. In humans, the length is about 10 kb ( kilobases ), after several cell divisions ( 50-100 ) can be reached a length of about 4-6 kb. Thereafter, the cell goes into the resting phase and no longer divides. With each cell division, a piece (about 100 nucleotides) of the telomeres is lost. Telomerase preventing certain cells in the restoration of telomers, that the chromosomes are shorter with each cell division, and thus bypasses the end replication problem.

This problem arises because the DNA polymerase δ in discontinuous DNA strand also replicated from 5 'to 3'. Discontinuous string on the DNA polymerase δ synthesized starting from RNA primers Okazaki fragments until it encounters an existing RNA primer. By exonuclease activity of the RNA first base is from the 5 'end of the primer. The complete removal of the RNA primer accept so-called flap endonucleases. The interstices of the discontinuous DNA strand will also be closed by means of the polymerase δ and filled with deoxynucleotides. A ligase the remaining strand breaks. Since the discontinuous strand DNA may be replicated only so long as the binding of an RNA primer is possible to a piece of minimal the length of the RNA primer is left. Depending on the binding of the last RNA primer this piece can be much longer (up to 100 nucleotides). Thus, sequence information go to the DNA ends is lost and the chromosome length decreases with each cell division and the associated DNA replication (see aging).

In most normal cells, the telomerase activity is not detectable. Active telomerase is only in unicellular organisms as well as in continuously dividing cells such as bone marrow cells, cells of the germline (see also germ cell), embryonic cells ( = embryonic stem cells), stem cells and certain types of immune cells in multicellular organisms.

Telomerase is also active in cancer cells and helps them to fact infinitely often to divide and proliferate in the body. Non- malignant cells can only a certain number of cell divisions undergo (so-called Hayflick limit).

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