Sciencemadness Discussion Board

Aging in unicellular organisms?

Wolfram - 15-2-2004 at 11:02

Unicellular eucaryots reproduce often by dividing. When a yeast cell divides one of the yeast cells is the old "parrent" yeast cell and the new one is the "child" yeast cell which is identical to its parrent. When the "parrent" yeast have devided a number of times it looses its ability to divide and dies.
Is it like this also for other unicellular eucaryots (for example protozoa)? I mean is it like this that one of the cells could be said to be old "parant" and one the new one "child"? At least one of the cells must have the old genome and one the new one so do the old cell "age" and die?

[Edited on 15-2-2004 by Wolfram]

amoeba

If_6_was_9 - 16-2-2004 at 10:19

I read something about amoebas being immortal. When one divides both are sort of like identical twins the way I understand it. DNA is made up of two strands bound together like a zipper by hydrogen bonds. When its duplicated, the DNA starts to unzip while new nucleotides form on the open strands. Eventually two new strands form which are identical as long as no mistake was made. Each new strand has half the nucleotides of the original DNA. Enzymes control the process.

[Edited on 16-2-2004 by If_6_was_9]

hmmm..

Wolfram - 16-2-2004 at 14:12

hmmm.. still one of the amoebas (at least to the genome) must be the oldone and the other the newone.. dont you think? So for how long can the old amoeba live, and divide.

chemoleo - 16-2-2004 at 14:33

Hmm, I thought all eukaryotes have a finite number of cell divisions. This is called the Hayflick limit by the way, so if you look that up you can get lots of more info.
Prokaryotes (bacteria), conversely, don't have this limit.
The reason why there is this limit, is, as far as I remember, because bacteria have a circular genome. That means, there are no ends, and thus no need for telomerases etc. that stop the ends from degrading.
I don't know if there are eukaryotes with circular genomes - if, then they are some of the most simple ones.

Answer

Wolfram - 16-2-2004 at 15:47

Man, unicellular eucaryots like yeast or protozoa can not have a limited number of celldivisions because they would be extinct even before they started. They don´t have circular genome eighter, but they have active telomerase that elongates the telomeres. Telomerase knockout yeast stops to reproduce (divide) after a number of cell divisions.

chemoleo - 16-3-2004 at 10:07

Quote:
Man, unicellular eucaryots like yeast or protozoa can not have a limited number of celldivisions because they would be extinct even before they started.


Interresting. where did you hear that from?
All somatic cells from multicellular eukaryotic organisms have a limit to their number of cell divisions. This is called the Hayflick limit. Check it if you don't believe me.
Germline cells such as oocytes/sperm don't divide by themselves, as the two have to combine in order to divide! There are reasons why germline cells don't have shortened telomers, although I fail to remember why that was again (also, telomerases are not perfect in maintaining the chromosome ends - so old people DO have shorter telomers. Conversely, an overly efficient telomerase activity (like an additional gene encoding it, i.e. in transfected mice) produces cancer. So telomerase is by no means the solution to aging and such).
Anyway, at the time of sperm/oocyte fusion, the Hayflick limit is set to zero once again (if it was ever offset in sperm-producing cells).

Only cancerous cells from multicellulars divide indefinitely, like the cells from Henrietta Lacks, which are used today, 50 years later, for experiments (HeLa cells).

As to circular genomes - they do indeed explain the lack of telomerases in prokaryotes (bacteria). As I said I am unaware of eukaryotes with circular genomes, but I couldnt exclude some simple ones exist.

At last - there has been debate about it: Man, even if it could extend its lifespan by nutrition, health, cures for age related diseases and such, the ultimate death would still come when all cells stopped dividing (which would be around the age of 200 IIRC). So in fact noone dies because the Hayflick limit, as problems set in way before that!

[Edited on 16-3-2004 by chemoleo]

If_6_was_9 - 16-3-2004 at 16:50

Cancer appears to be immortal
Quote:

In his earlier work, Dr. Shay found that the enzyme telomerase was present in specialized reproductive cells and in most cancer cells that appear to divide indefinitely. Thus, the gene which codes for telomerase has been nicknamed the "immortalizing gene". Telomerase works by adding back telomeric DNA to the ends of chromosomes, thus compensating for the loss of telomeres that normally occurs as cells divide. Most normal cells do not have this enzyme and thus they lose telomeres with each division.


http://www.accessexcellence.org/LC/ST/st10bg.html

http://www.accessexcellence.org/WN/SUA04/telomerase.html

[Edited on 17-3-2004 by If_6_was_9]

BromicAcid - 16-3-2004 at 17:10

http://www.news.wisc.edu/story.php?id=5528

http://www.popsci.com/popsci/medicine/article/0,12543,188371...

I read about this a long time ago and searched it in google (Immortal skin cells cancer burn) and got a crap load of hits. Turns out a bunch of researchers were trying to figure out how to best grow skin when one of their cultures suddenly didn't die off. The same culture has been spread to hundreds of thousands of other plates and been researched, it does not appear to be cancerous yet they do not seem to give a damn for the Hayflic limit.

gil - 19-1-2007 at 00:10

Let's close the books and look at THE REAL WORLD :
HOW BIG WAS THE BIGGER SPECIMEN YOU REMEMBER?

Wath was the final appearance? like what material?
WHATH ARE YOUR REAL EXPERIENCE WHITH IT? ANY PARTICULAR SEASON, WHITH hiGHER INCIDENCE?

CAN A CATARR(SPUTUM,SCRACCHIO,SINUS MUCUS) MOVE ON IT' S OWN?

WHY EXACTLY SINGAPORE PROHIBITED CHEWING GUMS?

[Edited on 19-1-2007 by gil]