Question

At the end of replication, about 100 nucleotides remain unreplicated on the lagging daughter strand. What mechanism (and what enzyme) in eukaryotes solves the problem of shortened DNA ends?

Answer 1

The shortened DNA end problem is solved with the help of specialized DNA "caps" called Telomeres, which prevents the loss genes at the tip of the chromosome. Telomeres consists of thousands of short DNA repeat, usually 5' TTAGGG 3' in human beings and mammals. The repeats are slowly lost in cell divisions. This phenomenon is associated to cell aging and limiting the number of cell divisions a cell can undergo. Telomeric-binding protein like TERF,TRF, TRBF have the funtion to bind the telomeric DNA. The telomeric binding protein refers to TTAGGG repeat binding factor-1(TRF1) and (TRF2). TRF are double stranded proteins helping in the bending, looping of DNA, hence in the formation of T-loops.However humans have a complex call Shelterin, which consists six subunits.

Many cells have the ability to reverse the loss of telomeres by the action of an enzyme called Telomerase. Telomerase is an RNA-dependent DNA polymerase that extends the telomeres at the chromosome's end. For eg. cancer cells, germ cells.