It all depends on our DNA, our genes, damage to our DNA and our DNA’s ability to repair the damage effectively and in time.
When we are young and healthy, free of disease and wrinkles and full of energy and life, our DNA is healthy and functioning optimally. This means our DNA, which is organised into genes, are coding 100% correctly for certain cellular functions, for specific proteins and enzymes, for organs to function correctly and for us to be healthy and alive.
Our DNA molecules in the nucleus of every cell are bombarded by baddies – some from the environment and some from inside our bodies – and some of the important bonds in this molecule might break. But every cell in our bodies has a full army of enzymes available to counteract these breaks, and to repair the DNA.
Only when the damage happens at a faster pace than the repair, will the damage become apparent. Only when the army of repair enzymes cannot repair vast DNA damage fast enough, will it be possible for a damaged bit of DNA to slip through the cycle.
The problem is that in some cases even a small change in the DNA might lead to a huge problem, and in other cases bigger changes in the DNA might not lead to any problems. It depends on where the repair team cannot keep up. Although we know which part of the DNA is most vulnerable, we - unfortunately – do not know where the baddie will attack.
When DNA is damaged, a single break in the DNA strand might be repaired, but it might be repaired with the wrong building block. One change in the row of building blocks can alter the code in a gene which codes for the production of a certain protein. Interruption of the production of the specific protein might lead to either a small health problem or a huge one. If the affected protein is insulin, you might develop diabetes. Or the change in code can switch on a cancer gene.
Take a look at the following example of sun damage to the skin. Ultraviolet rays in sunlight causes DNA damage. If you are exposed to sunlight too long and too often, you might stress your DNA repair enzymes to such an extent that the damage may not be repaired or not repaired correctly. The incorrect DNA strand will duplicate and divide and all the subsequent cells will carry damaged DNA. If this DNA now codes for cancer, or even if it just doesn't code for the production of an essential protein or enzyme that your body needs to function normally, you are in trouble. As soon as the number of cells with the damaged DNA reaches a critical mass, you might start noticing the result. In the case of DNA damage caused by UV rays, it might be wrinkles, or it might be a skin lesion that turns into melanoma, one of the deadliest cancers of all.
As we grow older, our DNA’s ability to repair itself also slows down, and more damaged DNA might slip through the cracks and into the process of cell division before the damage can be repaired effectively and correctly.
We don’t know which exposure to which ray of UV light will be the one to cause the damage to the cell that might not be repaired in time. We do not know which breakage in DNA caused by which cigarette, will be the one that cannot be mended in time. We do not know the moment that the damage load to a specific cell will be too much or the exact damage the DNA repair team won’t be able to cope with. But we know that if you bombard the cells with potential baddies (damage causing factors), you might overload your DNA repair team.