What is a telomere?
A telomere is composed of partially double stranded and partially single stranded DNA , encapsulated in protective protein, and is seated at the end of a chromosome . Telomere in Greek means end piece. A telomere does not occur in prokaryotes with an annular chromosome. Old cells have chromosomes with shorter telomere than young cells. An exception to this, however, was discovered in 2003 at the Vaal storm petrel , which telomeres with age of the bird are actually increase in length. Shorter telomere length has often been associated with a higher risk of cancer and cardiovascular diseases and diseases of aging in general, but it is still unclear whether this is a causal relationship.
A telomere is like the plastic tip of a shoelace. On each division fray the ends a bit and eventually the cell can no longer divide and die. Human cells reach this stage after fifty, sixty divisions. If, the telomere length is maintained, the cell may continue to divide without death. Under the microscope, a telomere visible as a luminous dot.
Elizabeth Blackburn , Carol Greider and Jack Szostak won the 2009 Nobel Prize in Physiology or Medicine for their discovery of the protective effect of telomeres during cell division.
T-loop
A telomere is composed of repetitive bits of DNA that the important genes protects against the shortening of the chromosomes. Also, the telomere is important for the stability of the chromosome. In humans, the repetitive piece of DNA consisting of the sequence TTAGGG and the telomere is between 3 and 20 kilo bases in length. Between the telomere of the chromosome, and the remainder is still a piece of which is 100 to 300 kilobases in length. As a result, it can be a sort of lasso telomere, T-loop, forms. The sequence varies from one organism, but usually contains a lot of GC ( guanine and cytosine ) nucleotides.
During the cell division , the DNA is through replication doubled. The enzyme DNA polymerase , however, can not replicate the end of the chromosome, since it falls off to drop out of the DNA. As a result, the chromosomes will be shorter at each cell division. The enzyme telomerase that a reverse-transcriptase to make is, a telomere may get longer and is present in the germ line cells , which make the germ cells, stem cells , cancer cells and protozoa . Telomerase composed of an enzymatic portion and an RNA portion, the complementary sequence.
Responsible gene
The gene is responsible for the formation of telomerase is in 1998 by Geron Corporation in California cloned and introduced into cells. These cells have two years shared without any form of aging. They seem to have become immortal.
Repair mechanism
Each cell has a DNA repair mechanism that repairs damaged DNA. If the DNA is badly damaged and can not be repaired, the cell stops parts or dies. If the telomere 4 kilobases has become short, we can make no longer a loop and sees the DNA repair mechanism, the end of the chromosome as a broken chromosome so that the cell will stop with parts or death.
Cloning
When clones of cells, one starts from cells that already have shorter telomeres. So the new organism leaves with shorter telomeres.