You and I are mere collections of cells. All be it extraordinary and far too complicated to entirely understand, that exists as blobs, functions together to let us experience this surreal journey of life for a while and then *bam* we die.
Animals display an astounding variety of maximum lifespan ranging from some insects (mayflies, mosquitoes) that live for 2-3 days to bowhead whales and giant tortoises that can live up to 200 years.
The record of the longest living animal belongs to a quahog clam, which was alive for 507 years. Some animals like – hydra have found remarkable ways to cheat death. Why does such a non-uniformity of longevity exist in the animal kingdom?
Some animals die as soon as they are born while others get a free pass to near immortality. Why does this happen? Cells have their deaths programmed into them (like a self-destruct button). Cells divide to replace the injured or worn-out cells. This is viable for a fixed number of divisions.
In humans, this magic number is 50. Simply put, our cells are capable of 50 or so divisions before undergoing “cell suicide” or as biologists call it – ‘apoptosis‘. In mice, that lives for 2/3 years, the magic number drops down to 14-25. Galapagos tortoise, on the other extreme, has about 125 divisions and can live for 150 years.
But what causes this limit? Why is there a “self-destruct” button in our cells in the first place?
The answer lies in the chromosomes (tightly coiled DNA). ‘Telomeres‘ are the end part of the chromosomes that are responsible for the protection of the DNA from any damage. With every cell division, these become a bit shorter i.e. a part of the telomere gets cut off (instead of our important DNA).
Consider this example – you need 100 copies of a document and with every copy which is printed out, the last letter gets erased. If this continues inescapably, the complete document would be obliterated.
In the same way, the cell detects the reduction in the DNA and kills itself before inflicting permanent damage to the DNA. Okay, so what if we just insert more telomere in the cells? Then it won’t ever finish and we won’t age, right? Um, there already is a cell that does that – cancer cells. These cells maintain the telomere length for unlimited growth (which forms tumours) by reactivating the enzyme – telomerase.
Apart from this, mitochondria (you probably remember it being the ‘powerhouse of the cell’) also seem to have a substantial role in ageing. They contain their DNA (different from nuclear DNA) which allows them to function as an individual entity.
While undertaking its primary function – the production of energy, they release out (ROS) Reactive Oxygen Species (a molecule that easily reacts with other elements of the cells to cause destruction) as a byproduct that damage the nearby mitochondrial DNA (mtDNA). Sort of like a factory that generates waste materials during the manufacturing process that destructs the nearby surroundings.
We are constantly under attack from the environment and our bodies accumulate damage over time. This alters the systems in our body that work together for our survival. Everything, ranging from our diet, our lifestyle, to our circadian rhythm (sleep-wake cycle), affects the process of ageing.
As age increases, apart from supposedly increasing wisdom, one also becomes more prone to several illnesses. The muscles grow fragile with constant wear and tears, the immune system weakens, mental disorders prevail, primarily including Alzheimer’s and Parkinson’s disease.
Benjamin Franklin, remembered for wit, wisdom and elegance of writing, rightly quoted: “A long life may not be good enough but a good life is long enough”. How are you looking out for it?