Quantity of free BiP in the ER lumen determines the relative proportions of monomeric and dimeric Ire1.

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#Unit 1. Molecules and their Interaction Relevant to Biology

The two forms of poly(Pro)

all cis (I) or all trans (II) peptide bonds. 

poly(Pro) I as a right-handed helix with 3.3 residues per turn 

poly(Pro) II is a left-handed helix with 3 residues per turn.

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#Id: 8471

#Unit 1. Molecules and their Interaction Relevant to Biology

poly(Pro) helix are stabilized by water molecule hydrogen bonding

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#Id: 8472

#Unit 1. Molecules and their Interaction Relevant to Biology

Poly(Gly) chains also adopt secondary conformations. 

In the solid state poly(Gly) has been shown to adopt two regular conformations designated I and II. 

State I has an extended conformation like a β strand whilst state II has three resides per turn and is similar to poly(Pro).

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#Unit 1. Molecules and their Interaction Relevant to Biology

Beta sheets usually have their B strands either parallel or antiparallel

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#Unit 1. Molecules and their Interaction Relevant to Biology

β Sheets in proteins contain 2 to as many as 22 polypeptide strands, with an average of 6 strands. 

Each strand may contain up to 15 residues, the average being 6 residues.

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#Id: 8475

#Unit 1. Molecules and their Interaction Relevant to Biology

Repeat period is shorter for the parallel conformation (6.5 Å, vs. 7 Å for antiparallel)