The Hayflick Limit

The Hayflick Limit

 

The Hayflick limit was discovered in 1961 by Dr. Leonard Hayflick and refuted the prevailing thinking of the day that animal cells were for all purposes immortal.  In simple terms the Hayflick limit is the maximum number of times that an animal cell can divide.  In humans this turns out to be around 60 times before the cell can no longer divide.  This limit in the number of times a cell can divide to due to a shortening of the cell’s telomeres.

Hayflick limit

Telomeres marked in green

 

Telomeres are segments of DNA found at the ends of chromosomes (the green segments in the picture above).  They can be thought of as the blank pages you find at the beginning and end of a book, if they get ripped out you do not lose any of the story.  Unlike a book where the blank pages remain in place for the life of the book, telomeres shorten every time a cell divides until the segments are worn down to nothing as a person ages.  This is due to the nature of DNA replication, which is explained below.

 

DNA Replication

          1- Initiation the twisted double stranded DNA unwinds and splits in half.

          2- Elongation DNA polyermase reads the DNA in the 5 prime to 3 prime direction.  The 5 prime and 3 prime refers to the structure of the sugars used to form the backbone of DNA.  For our purposes it simply gives us a direction.  Think of DNA as a two way street with DNA polymerase running in each direction from 5 prime to 3 prime.

DNA replication

Leading strands and lagging strands

 

Okazaki fragments.  Now DNA only unwinds in one direction and DNA has to be read in the 5 prime to 3 prime direction.  What this means is that one side of the DNA can be copied from start to finish in one large segment.  The other half must be copied in segments, where the DNA unwinds and DNA is copied up to the previous segment.  DNA polymerase must then stop and wait for more of the original DNA must be unwound.  Now this is where the Telomerase comes in, DNA polymerase needs a segment of DNA to latch onto in order to start.  So the very tail end of the telomere is not copied because there is no more DNA for DNA polymerase to latch onto in order for it to be copied.  This segment of DNA is then lost making chromosome slightly shorter each time it is replicated.  Thus as a person ages the telomeres shorten and this has everything to do with Rau Le Creuset and Tsunade.

Hayflick limit

Shrinking telomeres

 

          3- Termination, DNA finishes replicating the DNA and the whole thing falls apart as the two new DNA strands rewind, returning to their standard state.

 

The Hayflick limit in Gundam Seed

Rau Le Creuset is the 28 year old ace pilot and commander from ZAFT who needs to take medication to manage an unnamed, but a clearly debilitating set symptoms due to his being a clone.  These seem to include muscle spasms, pain, and mood swings.  A clone is an organism whose DNA is identical to the original and at the present time the technology does not exist to create a human clone.  It has been done with other animals such as sheep, shown below.

 

Dolly the sheep

Dolly the sheep

The first cloned sheep

 

Now sheep have an average lifespan of 10 to 12 years, but Dolly only lived for 7 years despite being born healthy.  The reason for this is due to the genetic age or the telomere length of the donor sheep.  While Dolly was only seven years old chronologically the DNA in her cells was 12 years old effectively shortening her lifespan.  Commander Creuset is stated to be 28 years old in Gundam Seed (pictured on the left), and we can assume due to having a child, Al Da Flaga (pictured on the right) was likely between 30-50 when he had a clone created.

Rau Le Creuset

Rau Le Creuset

Al Da Flaga

Al Da Flaga

 

 

 

 

 

 

 

This makes Creuset’s genetic age somewhere between 58 to 78 years old.  While the commander still looks young his cells are entering or are well into old age by the start of Gundam Seed.  The medication he is seen taking is most likely being used to treat the cellular breakdown of his own body.  While these medications do not exist at this time there is no scientific reason why drugs to treat cellular breakdown and the degradation of DNA will not exist at some point in the future.

Rau Le Creuset drugs

Experimental medication

 

While the technology to create and treat the medical conditions faced by cloning does not exist at this time, the science is there so the existence of Rau Le Creuset is

 

plausible

plausible

 

The Hayflick limit in Naruto

Now for the Naruto fans out there we have Tsunade and her Creation Rebirth technique both which are shown below.  The following is taken from the Naruto wiki as I haven’t seen the mange volume or anime episode that covers this.  The creation rebirth technique is a skill where Tsunade uses her chakra to stimulate the rapid growth and development of new cells instead of regenerating old cells.

Tsunade

Young Tsunade

Tsunade

Genesis Rebirth

Hayflick limit

Old Tsunade

 

The actual technique is not what is going to be covered here but the stated downside of this skill, namely shortening her lifespan.  The healing of injuries by using rapid cell division would quickly cause the cells of the body to reach the Hayflick limit raising the individual’s genetic age faster than their chronological age.  This effetely gives Tsunade the same problems faced by Rau Le Creuset and Dolly the sheep.  It also makes her look extremely old given the way other characters react to her true form.  As such, while the actual technique is not possible, the side effects of that skill are confirmed.

Confirmed

Confirmed

Thank you for reading and questions, comments, or suggestions are welcome.

 

Sources

https://www.ncbi.nlm.nih.gov/pubmed/11413492

https://www.the-scientist.com/?articles.view/articleNo/42256/title/Of-Cells-and-Limits/