Observational learning

TLS Online TPP Program

#Id: 8480

#Unit 1. Molecules and their Interaction Relevant to Biology

Antiparallel sheets are usually arranged with all their hydrophobic residues on one side of the sheet. 

This requires an alternation of hydrophilic and hydrophobic residues in the primary structure of peptides involved in antiparallel b-sheets because every other side chain projects to the same side of the sheet

TLS Online TPP Program

#Id: 8481

#Unit 1. Molecules and their Interaction Relevant to Biology

Turns are classified into several classes, like 

β-Turn  (I, II, I’, II’) 

α -Turn 

γ- Turn

π -Turn

TLS Online TPP Program

#Id: 8482

#Unit 1. Molecules and their Interaction Relevant to Biology

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.