At the core of every organism lies a particular cellular alphabet which encodes the information for the lifelong development and maintenance of that organism. This genetic library, or genome, of an organism is located in the nucleus and consists of the complete set of DNA segments that are packaged into chromosomes. Each chromosome has one long twisted DNA molecule which is made up of hundreds to thousands of genes that encode genetic information in the specific sequence of the four types of nucleotides: Adenine, Thymine, Cytosine and Guanine. The deoxyribonucleic acid of all organisms is composed of the four kinds of nucleotides but the differences in their sequencing is what distinguishes one organism from another. Hence, all life forms are essentially built from the same genetic code: DNA. Quite literally, DNA is the equivalent of life.
Now, for each of the genes stocked in DNA to be transmitted to each of our cells, the DNA molecules must be replicated. This is done by the process of mitosis or the division of the nucleus. Before a cell prepares to divide, the chromosomes are duplicated so each of the two daughter cells is the genetic equivalent of the parent cell. During this synthesis period, the two strands of the DNA double helix separate and the enzyme DNA polymerase begins to add nucleotides that are the complementary counterparts of the original DNA molecule. This is due to the fact that the four nitrogenous bases that are the basic building blocks of DNA always bind in a specific fashion: adenine always pairs with thymine and guanine always binds to cytosine. Since DNA polymerase can only add nucleotides to the 3' end of an already existing DNA strand, it has no way to complete the 5' end of the daughter DNA strand. This suggests that through consecutive rounds of replication, the DNA molecules would become shorter and shorter while losing sections of DNA sequences that code for genes until it reaches a critical point where no further cell division can take place. This phenomenon, called the "end replication problem", was pointed out by James Watson in 1972. Eukaryotic chromosomal DNA molecules overcome this problem by the molecular mechanism of telomeres.
Telomeres are appendages of non-coding, repetitive sequences of nucleotides located at the ends of linear DNA molecules such as those in eukaryotic cells. These protective "caps" found at chromosomes ends prevent the shortening of genes during DNA replication, make it possible for our cells to divide without the erosion of genetic units and ensure that genetic material is successfully passed down from one generation to the next. They also protect the chromosomes from fusing and connecting DNA with each other. Recent studies have also shown that telomeres correlate to aging and that telomeres play a significant role in the immortality of cancer cells.
As previously noted, eukaryotes have repeated nucleotide sequences on the ends of their chromosomes. For example, the...