as you age, the telomeres start aging.ok mice that were prematurely aged, added an enzyme, and essentially turned their telomeres back on. you can see it aftebefore the enzyme. after. >> their brain function improved. their fertility restored. it was a remarkable reversal of the aging process. >> reporter: look at this picture. the mouse on the right has bad skin, gray hair and is balding. but the one on the left had its telomere >> and you can see that essentially now, you have a dark coat color. that the hair is restored. that the coat has a nice, healthy sheen to it. >> reporter: even more dramatic, the change in brain size. this is before. the mice had 75% of a normal brain, like a patient with severe alzheimer's. after the telomeres were reactivated, the brain returns to normal size. as for humans, while it is just one factor, scientists say by looking at our blood cells and measuring the telomeres, you can tell how well you will age. the longer the telomeres, the better the chances for a more graceful aging. but as f

the key is something called a telomere. we all have them. they're the tips or caps of your chromo sowns, seen here in yellow. this is what it looks like in a young adult. as you grow older, the telomeres become damaged and frayed. as they stop working, we start aging and experiencing things like hearing and memory loss. scientist took mice who were prematurely aged, added an enzyme and essentially turned their telomeres back on. you can see it. before the enzyme. after. >> their brain function improved. their fertility was restored. it was a remarkable reversal of the aging process. >> reporter: look at this picture. the mouse on the right has bad skin, gray hair and is balding. but the one on the left had its telomeres flipped back on. >> and you can see that essentially you now have a dark coat color, that the hair is restored, and that the coat has a nice, healthy sheen to it. >> reporter: even more dramatic, the change in brain size. this is before. the mice had 75% of a normal brain, like a patient with severe alzheimer's. but after the