This news item was created by students Annie Dey, Christina Largay, Dave Thompson, Hope Gole, Shanta Subramanian and Tonya Collop as part of their Chemistry 210 Semester Project in WS99 under the guidance of Prof. Rainer Glaser.

Glaser's "Chemistry is in the News"
To Accompany Wade Organic Chemistry 4/e.
Chapter 23: Carbohydrates and Nucleic Acids.

For each of the following questions, please refer to the following article:

by Kathleen Doheny, Los Angeles Times, May 14, 1997.

Editorial Comments

Sunlight is beneficial to the human body, providing essential biological factors like vitamin D, but too much exposure can be seriously detrimental. The most common way to incur damage is through the ever popular activity of suntanning. Whether in a tanning-salon or out on the beach, the skin is exposed to ultraviolet (UV) rays when in excess can burn the skin as well as cause mutations in the DNA. UV rays, absorbed by molecules in the skin have enough energy to break DNA strands.

One of the most common mutations resulting from UV light is the thymine dimer, where two adjacent thymine bases in an amino acid sequence are incorrectly bonded to each other, making them useless for transcription. If the DNA is impaired, the essential proteins cannot be produced, leading to severe detrimental effects on cell function. The body has many mechanisms for repairing these "natural" mutations. The enzyme that is responsible for repairing T-T dimers is photolysase, which interestingly requires UV light to repair the damage caused by the rays. Unfortunately, many mutations remain uncorrected, and a large number of them may lead to skin cancer.

UV light is known to be one of the most dangerous carcinogens in our daily environment. There are three major kinds of skin cancers diagnosed every year, caused by UV rays: squamous cell carcinoma, basal cell carcinoma, and the most dangerous type melanoma. Each affects a different layer of the skin's epidermis, and there are many factors determining what particular type of cancer develops in an individual. Because everyone is vulnerable to these cancers with exposure to the sun and UV rays, scientists and dermatologists are advising people to use sunscreen and take other protective measures against UV light.

There is no guarantee that sunscreens protect against all three types of UV rays that are present in sunlight: UVA, UVB and UVC. UVB has been linked to the less dangerous squamous and basal cell cancers, and most sunscreens effectively block it. UVA is thought to be related to melanoma, and UVC is the direct cause of thymine dimers. As scientific knowledge about the effects of UV rays increases, so does the public's awareness that "soaking up the sun" is not as harmless as it once seemed.

Pertinent Text References
Chapter 23: Carbohydrates and Nucleic Acids


Question 1: What are the three types of skin cancer, and which is the most deadly?

A. Basal cell, squamous cell, and melanoma. Melanoma is the most deadly type as it claims approximately 7,000 lives per year.

Question 2: According to the article, how does sunscreen prevent skin cancer?

A. Sunscreens interfere with the UV induced mutation at the molecular level resulting in nonmelanoma skin cancer. Unfortunately, the ability of sunscreens to aid in the prevention of melanoma is still unknown.

Question 3: In reference to Wade Chapter 23, what is the basic structure of DNA? Be sure to include the correct base pairing as well as the materials composing the DNA backbone.

A. The base pairs cytosine-guanine and adenine-thymine are connected to a sugar phosphate backbone, coiled into a double-helical conformation with the base pairs stacked horizontally in the center.

Question 4: What DNA mutation is caused by UV radiation, and what is required for the body to repair these mutations?

A. UV radiation causes the formation of thymine dimers (bonding of two adjacent thymines in DNA strands). The body repairs the mutation by means of DNA photolysase. Ironically, since DNA photolysase is a photo-enzyme, it requires UV or visible light to conduct repairs.

Question 5:

Obviously, since tanning causes damage to DNA and increases one's risk of skin cancer should the government ban tanning salons and should the marketing industry cease using tanned models to promote product sales?