Question: why do we die

Sive Finlay answered on 17 Nov 2013:

Hi Ladybird 🙂
We die because our cells and bodies deteriorate with age.
There’s a constant turnover of cells in our bodies with new cells being produced and old cells dying and being broken down. Every time our cells divide they have to pass on copies of the genetic information which are the instructions for how cells should work. This means making copies of long chains of the base pairs (A, T, G and C) which make up our strands of DNA. We have huge chains of DNA which are grouped into separate chromosomes. At the end of each chromosome is a region of base pairs called telomeres. These are repetitive sequences of DNA base pairs which don’t code for any genes but their function is protect the rest of the chromosome from damage during the copying process. Think of them as being a bit like the plastic, fused bit at the end of your shoelaces which stops them from fraying. Everytime a cell is copied the DNA-replicating machinery doesn’t quite get to the end of the chromosome so telomeres get shorter with every cell division. So that means that the protective part of the chromosome is getting worn away and the “laces” are closer to fraying over the time. As the telomeres shorten there’s a greater chance of mistakes in replicating the rest of the chromosome. These copying mistakes usually mean that the genes’ functions are compromised so our cells and tissues don’t work properly – so we age and eventually die.
But death isn’t just caused by mistakes in copying DNA. Our bodies are essentially big machines with lots of gears and working parts that need to be kept in good working condition. But, as in any machine, eventually things get worn down and broken. So our hearts slow and don’t pump as strongly when we age which means that blood doesn’t circulate as well and the rest of the body might be lacking in nutrient or oxygen supply. Our joints wear down with constant use and the nerve connections in our brain and around the body don’t work as well when we age.
All of these factors combine together until eventually our complicated physiological processes can’t work together any more so we die.
Sive