Without telomeres, the main part of the chromosome containing genes essential for life would get shorter after each cell division. So telomeres allow cells to divide without losing genes. Cell division is essential for growth of new skin, blood, bone and other cells. Also without telomeres, chromosome ends could fuse together and degrade the cell's genetic blueprint, making the cell malfunction, become cancerous or die. Because broken DNA is dangerous, a cell has the ability to sense and repair chromosome damage. Finally, without telomeres, the ends of chromosomes would look like broken DNA, and the cell would try to fix something that wasn't broken. That also would make them stop dividing and eventually die.
Before a cell can divide, the chromosomes within it are duplicated so that each of the two new cells contains identical genetic material. A chromosome's two strands of DNA must unwind and separate. An enzyme (DNA polymerase) then starts to make two new strands of DNA to match each of the two unwound strands. It does this with the help of short pieces of RNA. When each new matching strand is completed, it is a bit shorter than the original strand because of the room needed at the end by this small piece of RNA. It is like someone who paints himself into a corner and cannot paint the corner.
