Cytokinins are defined as compounds that have biological activities similar to those of trans-zeatin.

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#Unit 1. Molecules and their Interaction Relevant to Biology

Parallel sheets are typically large structures; those composed of fewer than five strands are rare. 

Antiparallel sheets may consist of as few as two strands.

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#Id: 8479

#Unit 1. Molecules and their Interaction Relevant to Biology

Parallel sheets characteristically distribute hydrophobic side chains on both sides of the sheet

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#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

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#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.