This column is not about the end of the school year. This is not about my stress over graduation or my bittersweet thoughts regarding the end of my time at The California Aggie.
This column is about the end and the trouble scientists have determining when, exactly, the end is.
Some animals have a very certain end. Mayflies, for example, flit about on their elegant, glassy wings for only about a day. They find each other on chilly spring or fall nights, mate, lay eggs and then die.
On the other side of the lifespan spectrum are certain species of jellyfish and microscopic lake animals called hydra. These animals are called “immortal” for their ability to replace cells indefinitely. A jellyfish species called Turritopsis dohrnii goes through a process called transdifferentiation, which allows it to regenerate its entire body. When the jellyfish starts feeling old and creaky, it turns back into its youthful, polyp form and its cells start building a fresh body.
The fact that some animals seem to live forever has some scientists wondering why there has to be an end to human life at all.
Unless you’re a hydra or some freaky jellyfish, you will die. Scientists have kept a pretty good record of maximum animal lifespans. Mice live up to four years. Cats can live for 36. The oldest wild chimpanzee was 59, and an Asian elephant made it to 86. Humans can live a maximum of 122 years, followed by the lobster at 170 and the koi fish at 200.
Death is in our genes.
In the 1970s, geneticists Elizabeth Blackburn and Joseph Gall discovered that a tiny bit of DNA that bookends our chromosomes is responsible for aging. The DNA bookends, often compared to the little plastic nubs on the ends of shoelaces, are called telomeres. Telomeres hold repetitive sequences of DNA that don’t actually code for anything – sequences nicknamed “junk DNA.” Blackburn and Gall found that when chromosomes are copied during cell division, the telomeres get shorter.
After a certain number of cell divisions, telomeres simply get too short to divide again and the cell dies.
Turns out telomeres are far from junk.
This small-scale death is usually a good thing. When chromosomes copy, there’s always a chance of mutation. Too many divisions increase the chance of a mutation that will cause a disease like cancer. By limiting the number of cell divisions and chromosome replications, telomeres act as safety devices. On average, human cells can only divide 52 times.
Even knowing the important role of telomeres, some scientists want to know if it’s possible to keep cells dividing forever.
In 2004, a team of scientists from Korea did an experiment where they genetically engineered a species of roundworm to over-express a protein called HRP-1. This protein gradually increased the telomere length in the worms, and they lived several weeks longer than their non-mutated friends. These super worms even passed the trait to their offspring.
And in 2010, Harvard scientists tried an experiment where they bred genetically engineered mice that lacked the enzyme that shortens telomeres. Without the enzyme, the mice aged prematurely and suffered cell damage. But when the scientists injected fresh enzymes into the mice, aging reversed. The Benjamin Button mice even grew new brain cells, an unusual process in mice and humans.
Telomeres are important, but imagine a future where they’ve found a cure for cancer and a way to lengthen human telomeres. When would life end?
MADELINE McCURRY-SCHMIDT can be reached at firstname.lastname@example.org.