Link them in one sequence, you spell STOP. Use the identical letters in a different order, you spell POST. Same letters. Entirely different meanings.
This is how peptides work. Arrange 20 amino acids one way, and the body gets a hunger signal. Rearrange them, and the body gets a fullness signal.
The precision matters. Change the order enough to alter folding or receptor fit, and the signal can weaken, change, or disappear.
The body runs 7,000 distinct signals from just these 20 building blocks. Every peptide signal that regulates blood sugar, triggers appetite, dulls pain, or boosts immunity comes from rearranging the same 20 letters.
The building blocks are few. The variety they produce is vast.