When the sun shines on skin, the UV light activates those melanin-making cells. They start churning out sacks of melanin, also called melanosomes. Then they reach out to the skin cells they touch and move sacks of melanin over there.
The goal is to safeguard the DNA.
“When we get exposed to the sun, a lot of those melanosomes move around to protect the nucleus,” Cooper said. “They hover above the nucleus to protect it from DNA damage. Sometimes I’ll say it’s like a flying saucer up above the nucleus.”
Or you can picture it like an umbrella. The melanin-making cells open up to block the DNA from the sun.
When those sacks of melanin move into a skin cell, the melanin pigment makes the cell darker. That’s how skin gets browner in the sun.
That works so well to protect DNA that humans living in places with lots of sun adapted to better protect their skin.
“Someone who lives near the equator needs a lot more protection than someone who lives near one of the poles,” Cooper said. “So, genetic changes led people to have different skin tones.”
And that’s probably why giraffes have purple tongues.
The ancestors of giraffes adapted to live in places with lots of sun. Plus, today’s giraffes are the tallest living land animals. They spend about 12 hours every day chomping on leaves at the tops of trees. They grab those leaves with a purple prehensile tongue. It can grab leaves like a slimy, muscular tentacle.
That melanin-packed tongue protects the DNA in the tongue’s skin cells.
I guess you could say giraffes really lick the problem of UV damage.
Sincerely,
Dr. Universe
Ask Dr. Universe is a science education project based out of University Marketing & Communications at Washington State University.