Five burning questions you had about senescence (but were afraid to ask)

You couldn’t sleep last night because your mind was buzzing with these questions, right? Those fall colors on your daily walk have you thinking about life and death….

  1. What is senescence?

Merriam-Webster definition:the state of being old :  the process of becoming old; the growth phase in a plant or plant part (as a leaf) from full maturity to death
Senescence is the opposite of cancer: almost as if senescence was an adaptation to avoid cancer. If cancer is typified by “limitless replicative potential” then clearly non cancerous cells stop replicating (dividing) when they have reached their limit. But what determines that the limit has been achieved? Well, every time the cell divides into two, its DNA also replicates itself. With every replication, the DNA loses a little piece called “telomere.” Now each DNA has many telomeres which at the end, so bit by bit, with each replication, the DNA shortens by one telomere, till it loses its very last one. That is when senescence is reached… (usually after 40-60 divisions). 

2. Why do plants undergo leaf color change/fall every autumn?

The age-old theory is that this is an aging process and the old leaves must be disposed of regularly to give way to new ones. Plus, it conserves resources in the Winter as there are fewer plant parts to take care of… Recently, this remarkably orchestrated colorful extravaganza, which is also an intricately programmed senescence event has been attributed to: survival against pests!  Yes, it is now believed that leaves change color to scare away bugs so they will not cause damage.. Hmmm… now any new theories on why we develop grey hair????

3. What is the difference between senescence and aging?

As you may have gathered by now from reading this and our previous blogs on DNA damage and aging, aging is a complex process involving gradual loss of function or errors in function of cells/tissues/organs/systems. Senescence is a loss of replicative ability.

4. What are signs of senescence in humans?

What do you think are the “signs”… chime in here… type your responses, thoughts, ideas in the comment box… Meanwhile,here is something to listen to about the serendipitous observations of a scientist.

5. Do different parts of the body age differently?

Yes. It depends on various factors, Cells in any tissue are dependent on their stem cell reservoir and the support of other cells around them to keep the tissue going. Having long telomeres (those with many telomeres at the end of the DNA) is beneficial for these surrounding restorative cells to keep on dividing and replacing cells.  Short telomere cells (those with few telomeres) will tire out early as they will reach the end of their replicative ability much sooner. Stem cells also contain an enzyme known as Telomerase, which is also active in cancer cells and promotes elongation of telomeres. So Telomerase is an anti-aging/pro cancer enzyme. Elizabeth Blackburn, Carol Greider and Jack Szostak shared the 2009 Nobel Prize in Physiology or Medicine for “the discovery of how chromosomes are protected by telomeres and the enzyme telomerase“. Read more about this here too.

After senescence, we will next talk about 1. “diseases” of aging and 2. age-associated neurodegeneration… so stay tuned these final days of October…

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