It’s the 3rd decade of this century. We’re living at the pinnacle of human technology, with every year touching a new high in terms of our scientific and technological prowess. We’re using physics to manipulate electrons and atoms – which give us electricity and internet – the very foundation of modern life as we know it. Today, we’re surrounded by multiple products manipulating high energy particles – from cellphones to microwaves. The last time you went to a medical clinic to get an X-ray or MRI, you experienced radiation treatment, to put it simply. Although of course, all this is making our life easier. At the same time though, we’re facing new problems we’re largely unaware of. Radiation damage to DNA is real. It is known to produce harmful effects to our body as well as our internal organs, and we’re surrounded by it almost every moment of our lives.
Before delving deeper into this, it’s important to better understand radiation, and our DNA.
A Closer Look at Radiation
When energy is transmitted in the form of particles or waves through space or material medium such as aluminum, plastic, paper or lead, we term it radiation. Radiation can be either the ionizing or non-ionizing type. Ionizing radiation has the capability to interfere with the human body and break the chemical bonds of our DNA. Materials emitting α, β, or γ radiation are considered to be ionizing radiation – they tend to have much higher energy than visible light. UV rays too are another form of ionizing radiation. Ionizing radiation has high energy and shorter wavelength.
DNA of course, is the molecule that contains the genetic code for most functions of living organisms. DNA is a double stranded composition of polynucleotides, what we prefer to call the double-helix structure made up of subunits nucleotides. Each nucleotides is made up of four nucleobases A (Adenine), C (Cytosine), T (Thymine), G (Guanine) as well as deoxyribose (sugar) and a phosphate group which form the puzzle pieces of DNA. These four molecules are arranged together in a long line with different arrangements just like this.
Now there is one more line which is stacked together with the above line such that they form a structure of DNA and make living organisms work.
Radiation Damage to DNA and its Repair
Radiation can penetrate the closely knitted structure of DNA and can tear out the molecules. The DNA, which is the heart of the cell and contains all the instructions for producing new cells can be adversely affected, by direct damage to the cellular components or indirectly through water molecules.
In indirect action, the water in our body tends to absorb the particles and becomes ionized. H2O splits up into H2O+ and e- where both the particles are highly reactive free radicals. Additionally, H2O can also combine with one of the H2O+ ions to form H3O+ and OH· where, OH· is free radical and is highly reactive too. All these free radicals comes into contact with DNA to damage them. In direct way, the ionizing particles can come in direct contact with DNA and alter its structure.
Radiation damage to DNA can be caused by alteration to the bases, impact on strands, destruction of sugars, cross linkage and formation of dimers.
There are multiple ways radiation damages DNA strands too – single strand breakage or double strand breakage. When a single strand breaks, it is the bond between base and sugar that breaks whereas when double strands break, the entire DNA is disrupted and fixing it becomes rather difficult. Generally, DNA is regularly checked for repair wherein cells effectively fix the single strand breakage in 95 percent cases but during double strand breakage the cells find it difficult to repair the damage and alteration in DNA may lead to various diseases, such as cancer.
When bases are altered, base T can end up looking like baseG – leading to cells mistaking it. This change creates issues in the DNA duplication process, which occurs every time cell division takes place. So, instead of T, your cells may read it to be G, which would lead it to be paired with C instead of A (A pairs with T and G with C.) This could alter your DNA and can cause serious problems or in some cases it may be completely harmless.
Formation of dimers takes place when the DNA comes in contact with UV radiation. Instead of bases binding to opposite side they bind together on the same strand bases causing molecular lesions or pyrimidine dimers. Our cells generally fix this but if there are too many dimers around, it becomes difficult for our cells to fix these lesions. They are the primary cause of melanomas in human beings – which is a type of skin cancer. The diagram below gives an idea of how lesions are formed, while the other shows how DNA ligase, an enzyme which joins the broken nucleotides by restoring the bond between bases and the sugar.
DNA defects and diseases
If the radiation damage to DNA isn’t repaired during cell check or if an incorrect repair process takes place, it can lead to cancer or genetic defects – the sort of thins that’ll get passed on to future generations. Gene mutations are transferred from one generation to next- from either of the parent cell to the child, and can cause single-gene disorders, chromosome disorders or multifactorial disorders. Radiation damage can also lead to permanent disability, morbidity, lethality or injury to other parts of the body. It can cause cardiovascular, gastrointestinal and neural system disorders. The Chernobyl disaster is a notorious example of what radiation can do to flora and fauna of our planet.
As we continue to grow into a mature space faring civilization, we’re going to have to pay close attention to how we protect our astronauts from the shower of radiation they’ll face in space. Science needs more funds here.