Lecture 7 - DNA damage Flashcards
The Sun’s Energy
The sun’s rays are made up of more than just visible light. Visible light, part of the electromagnetic spectrum produced by the sun, reaches the earth’s surface. Ultraviolet light, a harmful part of the EM spectrum, is prevented from reaching the earth’s surface. The Sun Can Also Emit UV Radiation (Bad!!)
Plants Absorb the Red and Blue Part of the Visible Light Spectrum
Photosynthesis depends upon the absorption of light-energy by pigments in the leaves of plants. This energy is used in a process called the Calvin Cycle that leads to the synthesis of sugars (carbohydrates). The peak absorption for chlorophyll B occurs at the 500 nm wavelength of the sun’s radiation, while it is at wavelengths of 450nm and ~700 for chlorophyll A.
UV Radiation
From physics, E= hc/, which means that energy and wavelength are inversely proportional. Therefore, UVA with the longest wavelength, is the least harmful. On the other hand, UVC has the shortest wavelength and is the most damaging. However, we are mostly protected from UVC because of the stratospheric ozone layer, which absorbs it. UVB, between a certain range of wavelengths goes through unimpeded, and is therefore the part of the UV spectrum that is most detrimental to our health. Sunburns are the result of UCB damage, for example.
Beneficial Part of UV Exposure
Small amounts of UV are beneficial for people and essential in the production of Vitamin D. UV radiation is used to treat several diseases, including rickets, psoriasis, eczema and jaundice. The benefits of treatment versus the risks of UV radiation exposure are a matter of clinical judgment *Also understand the J-shaped curve Vitamin D is a free radical scavenger and is thus effective at limiting DNA damage. One hypothesis even posits that vitamin D supplements can reduce cancer risks. To make vitamin D in our bodies, we need the sun to convert the early progenitor into the useable form of vitamin D,1,25 dihydroxyvitamin D.
What is Vitamin D?
Vitamin D is essential for calcium uptake for bones and teeth. Low vitamin D levels can lead to osteoporosis (reduced bone calcium), rickets (soft bones in children), delayed tooth development in children.
Health Concerns of UV Radiation
Prolonged exposure to solar UV radiation may result in acute and chronic health effects on the skin, eye and immune system. Sunburn (erythema) is the best-known acute effect of excessive UV radiation exposure. Longer term, UV radiation induces degenerative changes in skin cells, fibrous tissue and blood vessels leading to premature skin aging, sun allergy and actinic keratosis. Another long-term effect is an inflammatory reaction of the eye. Skin cancer and cataracts are the most serious outcomes.
Ozone layer
The atmosphere has several layers.
The ozone layer lies within the stratosphere.Ozone primarily occurs in the stratosphere where it has a role beneficial to health. However, ozone can also exists in the troposphere (where we live) and here, it is considered a pollutant and a respiratory irritant.
During non-rush hour times, NO2 (another pollutant) reacts with ozone in reactions that are known as the zero sum reactions, because whatever chemicals are in the beginning are used up in the end. However, during the afternoon rush hours, lots of cars are emitting high concentrations of VOCs (volatile organic compounds). Instead of reacting with ozone, the NO2 reacts with VOCs, and instead of a zero sum, there is a net buildup of ozone. This is known as photochemical smog.
The Hole in the Ozone Layer
0.001% of air is ozone
The Antarctic ozone hole was discovered in 1985.
The ozone “hole” is a reduction in concentrations of ozone in the stratosphere.
The ozone hole has steadily grown in size (up to 27 million sq. km.) and length of existence (from August through early December) over the past two decades.Dobson units (DU) are the measure of ozone molecules. 1 DU = 2.7 x 10^16 molecules O3/cm2. The ozone hole occurs wherever an area has less than 220 DU and is poleward of 40N/S.
2006: largest hole ever recorded over Antarctica
The Ozone Blocks Most of the UV-B Spectrum
The shorter wavelength UV-C is blocked by the air as well as ozone from reaching earth.
Most of UV-B is blocked, except for the longer wavelength portion.
UV-A is unimpeded!!
What is Ozone and How is it Made?
- O2 + hv => 2O, [hv-sunlight less than 240 nm]
- O + O2 => O3 (ozone)
- O3 + UV light =>
O2 + O
( Ozone absorbs UV light)
What Happened to the Ozone Layer?
Refrigerators from the late 1800s until 1929 used toxic gases such as ammonia (NH3), methyl chloride (CH3Cl), and sulfur dioxide (SO2) as refrigerants. Several fatal accidents occurred in the 1920s when methyl chloride leaked out of refrigerators
In 1931, Dupont Chemical introduced the first coolant that was neither toxic nor explosive named R12 it is better know today as Freon.
Freon is odorless, colorless, nonflammable, and noncorrosive.
Freon is a chlorofluorocarbon (CFC)
CFCs are Haloalkanes
Breathing any amount of Freon is unsafe.
CFCs
Chloroflorocarbons are the Problem
CFCs are gases that are harmful to the ozone layer!
-Some of the common Freons used as refrigerants are: Freon 11, 12,13
CFCs are catalysts and can thus be recycled: just one molecule can destroy many ozone molecules!
Why is UV-light harmful?
-UV light is harmful because of light absorption.
-White light is composed of the entire spectrum of visible light.
-Why is it RED?
It means that all of the visible light spectrum is absorbed but red, which is reflected back.
- Molecules that make up a substance determine what wavelength of light is absorbed.
