Biomedical Engineering

No, this is not another post about sunscreen. Summertime means hotter days and warmer nights. In other words, more time in the pool and more time outside at night, and for fun memories, combine the two. Obviously, summertime led to a curiosity about two important mysteries. I was enjoying said scenario over the weekend, under the glow of the moon and the flicker of the lightening bugs. This piqued my curiosity about two things. First, why does your skin wrinkle in water, and second, what makes a firefly glow?

^{Not quite what I was thinking. Image Credit: geekologie.com}

Get Pruny

Pruned fingers and toes are a mystery to every child (and probably most grownups). It turns out that the outermost layer of skin is covered with oil called sebum. Sebum is important for moistening or lubricating skin as a means of protection. It is also a responsible for making skin a bit waterproof. A long swim, bath, or shower will wash away the sebum, allowing the water to penetrate into the outer layer of skin. Another reason wrinkles may occur is the same top layer of skin also contains dead keratin cells. Keratin strengthens skin and helps to keep it moist. The dead cells easily absorb water and swell after extended periods in the water; however, living keratin cells deeper in the skin do not absorb water, so as the dead cell layer expands it takes up more surface area. Since the dead cell layer is still connected to the living cells beneath, the stratum corneum top layer wrinkles to give the expanded cells a place to go. A follow up question is why does it only happen on your fingers and toes? This is because hands and feet have the thickest layer of dead keratin cells.

^{Image Credit: Flickr/Mathew Wilson}

Research is being done to identify the exact mechanism that causes fingers and toes to wrinkle. Some scientists' think that is caused by vasoconstriction due to the glomus bodies (body temperature regulators in the skin) lose volume, which then pulls the skin structure downwards to produce wrinkles. Submersion in water also seems to cause nerves to "shrink" and patients who have lost nerve function of their hands have little to no wrinkling in the fingers.

Get the Glow

My Nana told me that fireflies glow because they have a golden ring on their back. I was very disappointed when I finally managed to catch one and didn't get my golden prize. Still, when I finally did learn why fireflies glow (which was as I wrote this post) I was equally awed as I would have been with a golden ring. Fireflies glow to attract a mate (a ring would also do to attract a mate.) Each firefly species has its' own particular pattern which it flashes as a way of communicating between the males and females of the species. Fir

eflies of one species will fly around and dive steeply just as the flash begins and turn upward to make a distinctive J-shape pattern of light. The female fireflies watch from a tree branch or in the grass, and respond with a flash when she recognizes a flash

from a male of the same species.

^{Image Credit: http://theworldsight.blogspot.com}

The glow is caused by a combination of cells and an enzyme. Cells in the firefly's tail produce the luciferase enzyme (which also serves as a way to protect the firefly from predators - apparently it doesn't taste too good) by encoding the Luc gene with the cell's genome. The Luc gene specifies the sequence of amino acids that make up the luciferase enzyme. In order to become a functioning enzyme, the completed string of amino acids must bend and fold into a specific three dimensional shape. Once thousands of luciferase enzymes are produced they bind to a chemical called luciferin within the cell. The luciferase enzyme speeds up a chemical reaction that combines an oxygen molecule with luciferin to form oxyluciferin. This reaction requires energy, and it releases light. Thousands of luciferase enzymes result in a light that is bright enough to see. Learn.Genetics provides a very detailed animation of this process. Fun fact: Fireflies are actually a type of beetle and their larvae are also capable of this bioluminescence…they are known as glow worms!

^{This is a glow worm I know and love! (Come on, I haven't used a baby picture in weeks!) Image Credit: Sjlshots.com}

Resources

Everyday Mysteries

Why does my skin get wrinkly in water?

Kids Health

Why do fireflies glow?