From helping you with your math homework to teaching you how to throw a curve ball, there's nothing like growing up with a big brother as a role model. But as 15-year-old Jonathan Buchanan proves, sometimes, it's the younger siblings who are worth looking up to.
According to USA Today, the Chandler, Ariz. teen has been able to help his older brothers in a big way. Josh and Jordan, 16-year-old identical twins, were both born with sickle-cell anemia, a painful hereditary disease that affects the body's red blood cells.
Amazingly, Jonathan was a perfect match for his brothers, allowing him to donate bone marrow to Josh last year, and most recently, Jordan this past Wednesday. Josh is cured of his sickness, and thanks to their little brother, Jordan is expected to be cured as well.
"It's his [Jonathan's] DNA in us, so it made us feel better too," explained Josh to The Arizona Republic. "So he basically helped our life out a lot and he cured our sickle-cell."
Watch the video above to hear more from the inspiring brothers.
But Jonathan isn't the only teen whose selflessness is changing lives. High school senior Kyli Oleson is currently selling bracelets and T-shirts to raise money for Gavin Jack's heart transplant -- a teen who lives 160 miles away from her.
"When I found out about Gavin's condition, it really kind of hit home for me 'cause I realized he's a senior in high school and so am I," said Oleson.
Similarly, Chandler Lacefield's recent act of kindness is making a significant impact in the life of a fellow classmate. Knowing how badly her friend needed a car, the Texas teen sold her own Jeep to purchase her one.
"It's a sacrifice," Lacefield told NBCDFW.com. "But you always have to sacrifice for something good to come."
What do you think of Jonathan's incredible gift to his brothers? Would you donate bone marrow to a sibling if they needed it? Tell us in the comments or tweet @HuffPostTeen.