Charged R groups face the water
- The idea
- Predict
- See it
- Why
- Check
The idea
“Opposite charges attract, so charged R groups pair up in the core and nonpolar ones sit outside.”
Pairing opposite charges deep inside sounds tidy. But a charged group at the surface already has partners in the water around it.
The short version
The mistake: Opposite charges attract, so charged R groups pair up in the core and nonpolar ones sit outside.
What's actually true: In a protein folded in water, charged and polar R groups mostly sit on the surface. Nonpolar ones cluster in the core.
- Water is polar, so it attracts charged R groups like lysine and polar ones like serine. These hydrophilic groups do best on the surface.
- Nonpolar R groups like leucine and valine are hydrophobic, so they cluster in the core, away from water. These hydrophobic interactions help hold the tertiary structure.
- The core is the inside of the folded shape. Amino acids near either end of the chain can still end up there.
On the exam: Hydrophilic R groups face the water, and nonpolar ones hide in the core.