What difference do trans and cis configurations of amide groups bring to the polypeptide chain? Hi I was just wondering whether there would be any difference to the structure of the polypeptide chain, or any changes to a proteins characteristics, if it has more amide groups with a cis or trans configuration. Apparently the trans configuration is more stable, so more amino acids with a trans configuration can be found within a polypeptide chain. Does this pose any significant characteristic to a protein, and if so what is this characteristic?

> Apparently the trans configuration is more stable, so more amino acids with a trans configuration can be found within a polypeptide chain. Does this pose any significant characteristic to a protein, and if so what is this characteristic?

As you said, the _trans-_ form is energetically more favourable. However, in proline the _cis-_ form is energetically similar to the _trans-_ form. The _cis-_ structure introduces a kink or bend in the peptide chain which is seen in case of proline (see this section of wikipedia page on proline).