Radiation is the emission of energy from any thing. There are many varieties of radiation, starting from very high energy radiation like x-rays and gamma rays to very low energy radiation – like radio waves. UV rays are within the middle of this spectrum. They have more energy than visible light, but not as much as x-rays.
So Ultraviolet (UV) radiation is a form of electromagnetic radiation with wavelength from 10nm to 400 nm that comes from the sun and man-made sources like tanning beds and welding torches and transmitted in waves or particles, Most of the natural UV light people encounter comes from the sun. However, only about 10 percent of sunlight is UV, and only about one-third of this penetrates the atmosphere to reach the ground
As we said expect of sun, there are man-made sources that we can get Ultraviolet light from. For example, Sunlamps and sunbeds (tanning beds and booths) , Phototherapy (UV therapy) , Black-light lamps , Mercury-vapor lamps , High-pressure xenon and xenon-mercury arc lamps, plasma torches, and welding arcs ..etc
There are also different types of UV rays, based on how much energy they have.
UV radiation is divided into 3 main groups:
- UVA, or near UV (315–400 nm) are the most energetic and damaging of the three rays. Fortunately, UVC is absorbed by the ozone layer before reaching the earth’s surface.
- UVA, or near UV (315–400 nm) possess the lowest energy and is able to penetrate deep into the skin. Prolonged exposure has been linked to ageing and wrinkling of the skin. UVA is also the main cause of melanomas.
- UVA, or near UV (315–400 nm) possess higher energy than UVA rays and affect the outer layer of the skin leading to sunburns and tans. Basal cell carcinoma and squamous cell carcinoma are caused by UVB radiation.
And UV radiation has enough energy to break chemical bonds. Due to their higher energies, UV photons can cause ionization, a process in which electrons break away from atoms. The resulting vacancy affects the chemical properties of the atoms and causes them to form or break chemical bonds that they otherwise would not.
This can be useful for chemical processing, or it can be damaging to materials and living tissues. This damage can be beneficial, for instance, in disinfecting surfaces, but it can also be harmful, particularly to skin and eyes, which are most adversely affected by higher-energy UVB and UVC radiation.
So we should understand how UV light reacts in Cell’s DNA?
Ultraviolet (UV) light kills cells by damaging their DNA. The light initiates a reaction between two molecules of thymine, one of the bases that make up DNA. The resulting thymine dimer is very stable, but repair of this kind of DNA damage–usually by excising or removing the two bases and filling in the gaps with new nucleotides–is fairly efficient. Even so, it breaks down when the damage is extensive.
There are two ways that UV light can harm cells:
First way ultraviolet light can harm cells is by directly damaging DNA. This is something many of us are reminded of every spring and summer – it’s the cause of sunburn!
As the name suggests, direct DNA damage occurs when a photon of UV light hits DNA. DNA is a very large molecule that normally absorbs the energy it gains when hit with a photon of UV light and then quickly releases that energy as heat.
During the time after the DNA absorbs the energy and before it dissipates the heat, it is in a higher energy state and is more reactive; the shorter this reactive time is, the less likely it is that the DNA will undergo a harmful reaction. It turns out that DNA is extremely effective at dissipating the extra energy quickly, so it gets damaged less than .1% of the time it’s hit by UV light.
In the cases where damage does occur, how does it happen? There are different ways excited DNA can react, but the fusing of two base pairs is the most common. If two pyrimidine base pairs (thymine or cytosine) are next to each other, the two rings can fuse together. This type of reaction, called a pericyclic reaction, is possible because of how close the rings are and how their symmetries align.
The formation of a four-carbon ring between the pyrimidines makes it difficult for DNA replication enzymes to determine what base pairs should be across from the fused pyrimidines. A copying mistake like this can change how the DNA encodes a protein, resulting in an abnormal protein. If the mutation occurs in an area which codes DNA repair enzymes or tumor suppressing proteins, this mutation could lead to cancer.
Ultraviolet rays can also damage DNA indirectly. How? The story starts with melanin, a class of compounds which organisms produce that give their skin color.
The large system of freely-moving (delocalized) electrons that gives melanin its color is also what allows it to absorb UV light. Melanin isn’t the only light-absorbing compound in living things; chlorophylls and other bright pigments in plants also absorb light, acting in photosynthesis because of the large number of delocalized electrons in each molecule. When melanin is hit by a photon of UV light, it goes into an excited state, where an electron has increased in energy. In chlorophylls, this excited state starts the chain of reactions that results in photosynthesis. Melanin is different. Instead of becoming very reactive when hit by UV light, melanin releases the extra energy as heat; it reacts less than 1 out of every 1000 times it becomes excited. This allows melanin to protect more sensitive molecules, like DNA, from UV exposure.
UV damage occurs via two distinct types of mutations:
- Dimerizing mutations
- Oxidative mutations
The most common photochemical product in DNA is a cyclobutane pyrimidine dimer. This product forms when two adjacent pyrimidines (thymines, TT, or cytosines, CC) become linked covalently by their C=C double bonds. These four carbons form a cyclic ring (cyclobutane) that links the two pyrimidines, thus creating a chemical intermediate that is not normally found in DNA. This photochemical product causes a structural kink in the DNA that prevents the pyrimidines from base pairing, and prevents DNA replication.
2) Oxidative Mutations
UV exposure doesn’t always lead directly to mutations in the DNA. In fact, UV-A radiation commonly causes the creation of a free radical that then interacts with and oxidizes DNA bases. These oxidized bases don’t pair correctly during replication, causing mutations.
One example of this is a G to T transversion mediated by reactive oxygen species. The oxidation of guanine into 8-oxoguanine prevents the hydrogen bonding required to base pair with cytosine. Instead, during replication, 8-oxoguanine can base pair with adenine via two hydrogen bonds. When the second strand is synthesized, the base position originally occupied by a guanine is then replaced with a thymine, leading to a G to T transversion.
The genetic lesions produced by UV radiation are often repaired soon after they are formed, through a process called nucleotide excision repair.
A nuclease enzyme recognizes and removes a segment of DNA containing the lesion. Then, the polymerase inserts the correct bases and ligase seals the gap. However, if unrepaired lesions accumulate or the repair mechanism is faulty, it can lead to cell death, mutagenesis and even cancer.
UV-induced DNA damage has been directly linked to skin cancer, and DNA repair is an important protection against this neoplasm. This is illustrated by the genetic disease xeroderma pigmentosum where in a serious defect in DNA repair of cyclobutane pyrimidine dimers dramatically increases the rate of skin cancer. In other instances in which skin cancer rates are elevated, deficits in DNA repair may also be one of the causal factors.
We have found that treatment of cultured epidermal cells with ascomycin inhibits their removal of DNA damage by about 20% at 24 h.
And We have found that the cells with this variant polymorphism have an increased sensitivity of about 20% to a broad range of cytotoxic agents. The DNA deficits caused by immunosuppressive drugs or the OGG1 polymorphism can be overcome by the delivery of DNA repair enzymes in liposomes. The data suggests that deficits in DNA repair may contribute to increased rates of cancer, and that topical therapy with DNA repair enzymes may be a promising avenue for after-sun protection
and now we will compare between advantage and disadvantages of UV light On DNA and human being :
Positive (beneficial) effects of UV:
- Triggers vitamin D – UV from the Sun is needed by our bodies to produce vitamin D.
- Helps some skin conditions – UV is used in the treatment of skin conditions such as psoriasis.
- Helps moods – Research suggests that sunlight stimulates the pineal gland in the brain to produce certain chemicals called ‘tryptamines’. These chemicals improve our mood.
- Helps some animals’ vision – Some animals (including birds, bees and reptiles) are able to see into the near UV light to locate many ripe fruits, flowers and seeds that stand out more strongly from the background.
- Aids some insects’ navigation – Many insects use UV emissions from celestial objects as references for navigating in flight.
- Useful for disinfection and sterilisation – UV has positive applications in the fields of disinfection and sterilisation
Negative (harmful) effects of UV:
- Causes skin cancer – UV is an environmental human carcinogen. It’s the most prominent and universal cancer-causing agent in our environment. There is very strong evidence that each of the three main types of skin cancer (basal cell carcinoma, squamous cell carcinoma and melanoma) is caused by sun exposure. Research shows that as many as 90% of skin cancers are due to UV radiation.
- Causes sunburn – UV burns the skin. Sunburn is a burn that occurs when skin cells are damaged. This damage to the skin is caused by the absorption of energy from UV rays. Extra blood flows to the damaged skin in an attempt to repair it, which is why your skin turns red when you are sunburnt.
- Damages immune system – Over-exposure to UV radiation has a harmful suppressing effect on the immune system. Scientists believe that sunburn can change the distribution and function of disease-fighting white blood cells in humans for up to 24 hours after exposure to the sun.
- Damages eyes – Prolonged exposure to UV or high intensities of UV damages the tissues of eyes and can cause a ‘burning’ of the eye surface, called ‘snow blindness’ or photokeratitis.
- Ages skin – UV speeds up the aging of skin, since the UV destroys collagen and connective tissue beneath the top layer of the skin. This causes wrinkles, brown ‘liver’ spots and loss of skin elasticity.
- Weakens plastics – Many polymers used in consumer items (including plastics, nylon and polystyrene) are broken down or lose strength due to exposure to UV light.
- Fades colours – Many pigments (used for colouring food, cosmetics, fabric, plastic, paint, ink and other materials) and dyes absorb UV and change colour. Fabrics, furnishings and paintings need protection from UV (fluorescent lamps as well as sunlight) to prevent colour change or loss.
After all the necessary issues have been discussed on the UV Light , now we only have to say whether the surface wave is good or bad ? Or to put it another way , is it better to have a UV light ?
This question cannot be answered easily because it is a big mistake to say that the UV light is only good or just bad, because as we have said, there are a lot of advantages and disadvantages , Human life becomes much more difficult without the presence of UV light ..
So as we understand it we need to always protect ourselves from the strong waves and also take advantage of the proper waves which of course this is also done with a set of health guidelines and cannot be blinded doing .
And the speech of co-author Robin Wordsworth of the Harvard School of Engineering and Applied Science also confirms this as he said : ‘There needs to be enough ultraviolet light to trigger the formation of life, but not so much that it erodes and removes the planet’s atmosphere.’