Cancer cells and embryonic stem cells r immortal. How they escape death ?

Monday, June 15, 2009

In 1961 ,Dr, Leonard Hayflick discovered that when cells are taken from the body and grown in tissue culture on a laboratory dish, there is a limit to how long the cell line lives . After about 50 (the num varies with the kind of tissue) divisions, the aging cell line dies. Its known as Hayflick limit. This Hayflick limit has puzzled developmental biologists for decades. What causes the cells, after so many successful divisions, to abruptly break down ? How does a cell know its time is up?

But scientist now know all the answers !!!

The secret to immortality proved to be a short tag of DNA attached on the tips of the cell's chromosomes,known as telomere. This segment of DNA plays a key role in cell division. The telomere provides a place for the cell's DNA-copying machinery to latch onto the chromosome when the time comes for the chromosomal DNA to be copied into daughter chromosomes. However, every time the machinery attaches, the short bit of the telomere where the machinery sits down on the DNA is not itself copied, so the telomere gets a little shorter each time the cell divides. When the telomere reaches a minimal length after some 50 divisions, the cell can no longer replicate its DNA and lapses into senescence.

So, why Cancer and ESC cells are immortal ?

All cells possess a gene, known as the telomerase gene, which can add DNA back to the tip of telomeres. In almost all cells this gene is turned off early in development. If somehow, this gene is turned on then the cell become a cancer cell.

Embryonic Stem Cells also have the telomerase activity. But when they differentiate into other specialized cells they lose their telomerase activity ,as well as immortality. A few, however, are set aside, protected from the influences that trigger differentiation and shutting down of the telomerase gene. Called germ line cells, these embryonic stem cells have a fully functional telomerase gene and continue to divide, producing eggs and sperm that in their turn produce more stem cells in the next generation.

reference :

http://txtwriter.com/onscience/index.html

Giving Birth of extincted creature !!! possible or not?

Wednesday, June 3, 2009

The recipe for making any creature is wriitten in its DNA. If so,then its very much possible to regenerate an extincted organism from its DNA (when the complete DNA sequence of that organism is known).

Creating a living, breathing creature from a genome sequence that exists only in a computer's memory is not possible right now. But someone someday is sure to try it, predicts Stephan Schuster, a molecular biologist at Pennsylvania State University. It is only going to be possible with creatures for which we can retrieve a complete genome sequence. Without this, there is no chance,he added.

Usually when a creature dies, the DNA in any flesh left untouched is soon destroyed as it is attacked by sunshine and bacteria.There are, however, some circumstances in which DNA can be preserved. If your specimen froze to death in an icy wasteland such as Siberia, or snuffed it in a dark cave or a really dry region, for instance, then the probability of finding some intact stretches of DNA is much higher.

Even in ideal conditions, though, no genetic information is likely to survive more than a million years - so dinosaurs are out. "It's really only worth studying specimens that are less than 100,000 years old," says Schuster.

The genomes of several extinct species are already being sequenced, but turning these into living creatures will not be easy . "It's hard to say that something will never ever be possible," says Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, "but it would require technologies so far removed from what we currently have that I cannot imagine how it would be done."

But 50 years ago, who would have believed we would now be able to read the instructions for making humans, fix inherited diseases, clone mammals and be close to creating artificial life?

So, its for sure , oneday something like this will be done !!!

Its all about the fascinating science of Genetic Engineering and no one knows where to stop thinking !!!

Reference:

http://www.newscientist.com