Phase 1 (initial repolarization), fast sodium channels close

TLS Online TPP Program

#Id: 8483

#Unit 1. Molecules and their Interaction Relevant to Biology

The central bond in this case is the peptide bond, where rotation is constrained. The peptide bond is normally (99.6% of the time) in the trans configuration, constraining  to a value of w=+_180. For a rare cis peptide bond, w=0.

TLS Online TPP Program

#Id: 8484

#Unit 1. Molecules and their Interaction Relevant to Biology

The trans form is the more favoured state because in this arrangement repulsion between non-bonded atoms connected to the Cα centre are minimized. 

For most peptide bonds the ratio of cis to trans configurations is approximately 1:1000.

TLS Online TPP Program

#Id: 8485

#Unit 1. Molecules and their Interaction Relevant to Biology

Peptide bonds formed between Xaa and proline (Xaa is any amino acid) the cis to trans ratio is 1:4.

TLS Online TPP Program

#Id: 8486

#Unit 1. Molecules and their Interaction Relevant to Biology

All three kinds of bonds (N-Ca, Ca-Co, and the Co-N peptide bond) are single bonds.

TLS Online TPP Program

#Id: 8487

#Unit 1. Molecules and their Interaction Relevant to Biology

Co and N atoms of the peptide grouping are both in planar sp2 hybridization and the Co and O atoms are linked by a p bond, leaving the nitrogen with a lone pair of electrons in a 2p orbital.

TLS Online TPP Program

#Id: 8488

#Unit 1. Molecules and their Interaction Relevant to Biology