Archives of Ask A Scientist!
About "Ask A Scientist!"
On September 17th, 1998 the Ithaca Journal ran its first "Ask A Scientist!" article in which Professor Neil Ashcroft , who was then the director of CCMR, answered the question "What is Jupiter made of?" Since then, we have received over 1,000 questions from students and adults from all over the world. Select questions are answered weekly and published in the Ithaca Journal and on our web site. "Ask A Scientist!" reaches more than 21,000 Central New York residents through the Ithaca Journal and countless others around the world throught the "Ask a Scientist!" web site.
Across disciplines and across the state, from Nobel Prize winning scientist David Lee to notable science education advocate Bill Nye, researchers and scientists have been called on to respond to these questions. For more than seven years, kids - and a few adults - have been submitting their queries to find out the answer to life's everyday questions.
The skin's surface is covered with flattened cells rich in the protein keratin that makes our skin tough and water-resistant. These outer cells gradually slough off and are replaced by an underlying generation of new cells. But this outer layer, the epidermis, is not where age-related wrinkling happens---
Underneath the epidermis is a thicker layer, the dermis, composed of structural proteins that give skin strength and elasticity. These are mostly collagen fibers (80%) woven into a meshwork with elastin and other proteins to create a resilient biological polymer. As we age the amount of collagen declines, and both collagen and elastin fibers become looser, thicker, clumped, and even crosslinked to other fibers. The result is brittle and less elastic skin, leading to sagging and wrinkling.
What causes these chemical changes? Free radicals are electron-hungry molecules or atoms (oxidants) that are especially dangerous because they trigger a cascade of changes to biological molecules when electrons are pulled from one molecule to another, altering chemical structures and, hence, biological functions. Free radicals are byproducts of our energy metabolism and they are also generated by environmental influences, like air pollution, smoking, and ultraviolet radiation in sunlight.
We have antioxidant enzymes and molecules that protect us from free radicals, like vitamin C, vitamin E, and carotenoid pigments (from which vitamin A is formed). Carotenoids are the red, orange, and yellow pigments of plants. Tomatoes, carrots, and peppers are good examples, as well as fall leaf colors. We only get carotenoids from our foods, mostly fruits and vegetables. In spite of antioxidants, free radical damage occurs nevertheless. Another biological threat from energy metabolism is when glucose, a key fuel for our bodies, facilitated by free-radicals, crosslinks with proteins to form plastic-like molecules. These complexes, called age-related glycation end-products (AGEs), irreversibly alter skin proteins so that they are more brittle and less elastic. This is the same chemical process seen in the browning of cooked foods. That's right, our bodies cook as we age!
Skin's role in providing a barrier between the body and the environment makes it especially vulnerable to high-energy radiation from the sun. This is THE crucial lifestyle factor accelerating wrinkling of skin. Ultraviolet radiation causes DNA damage, damage to other molecules in the skin, and the generation of, ugh, free radicals. Accumulated damage to DNA in skin cells can lead to cancer, not a trivial concern. The skin has mechanisms to protect itself from damage and to repair damage that does occur. For instance, exposure to sunlight triggers tanning. Cells in the epidermis produce more melanin, a dark pigment that absorbs ultraviolet rays and dissipates their energy before they damage the skin. Human populations from regions with greater solar radiation have more melanin in their skin, a good example of evolutionary adaptation.
Isn't the body able to repair damaged proteins? Yes, but the repaired proteins do not work quite as well as before. Free-radical damage to DNA and chemical errors in repair of this damage likely contribute to the age-related decline in the fidelity of protein repair. And dermal proteins last a very long time - a recent estimate is that skin collagen has a half-life of about 15 years (so, in 15 years half of the collagen molecules now in your skin will still be there; the other half will have been broken down and replaced with new collagen). Any chemical changes to skin proteins will be with you for a long while.
So our skin wrinkles as we age because its structural proteins are gradually altered by the combined action of free radicals and glucose from the body's own energy metabolism and from the environment. This is a common feature of aging throughout the body. Why do different organisms age at different rates? This is the riddle of aging that I will not delve into here. This and other evidence shows that aging is under genetic control of repair mechanisms, but lifestyle influences can also be important. So remember that wrinkling of skin is under your control too. Prudent measures to protect your skin from ultraviolet rays will keep your skin from aging beyond your years.
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