# Question #f1b35

Dec 4, 2017

Not sure what you mean by "constrained", but it you mean more rigid, then you are right.

#### Explanation:

All proteinogenic ($\alpha$-)Amino Acids have the general formula

$H 2 N - H {C}_{\alpha} R - C O O H$.

Except for Proline, the R-chain (" Residu "-chain) is only connected to the "backbone" via the ${C}_{\alpha}$:

The structure for Proline is slightly different, in that the Aminogroup is part of the sidechain ( R):

This imposes some structural constraints on the peptide:
Due to it's sharp angle formed in the peptide bond between the Proline N -atom and the Carboxyl-group of the next AA, Proline is usually found at breaks in the secondary structure of the chain.

It is often found at the start and end of $\alpha$-helices and $\beta$-pleated sheets....