Because nucleosomal DNA wraps around the histone protein 1.65 times, the formation of a single nucleosome using ccc plasmid would create a writhe of –1.65 and thus change the linking number by an equivalent amount. As described above, when the change in linking number associated with each nucleosome was measured, the number was lower than this, approximately –1.2 for each nucleosome added.

This discrepancy is referred to as the “nucleosome linking  number paradox,”

#Id: 7694

#Unit 1. Molecules and their Interaction Relevant to Biology

                                                        aa motif / Coiled-coils

3.6 a.a / turn in helix 

abcdefg 'a' &'d’ are hydrophobic residues 'e' and 'g' are found to be charged amino 

7.2 a.a / 2 turns acids 

 —7 amino acids per 2 turns in the helix 

For every turn there could be one hydrophobic residue coming same side of the helix 

Ex: GCN4

#Id: 7695

#Unit 1. Molecules and their Interaction Relevant to Biology

                                                                        aa motif / Coiled-coils



#Id: 7697

#Unit 1. Molecules and their Interaction Relevant to Biology

                                                                 Greek Key Motif

Made-up of beta-sheets

Four adjacent antiparallel strands linked by loops

Three anti-parallel beta sheets are connected 3 loops

The pattern is similar to ornamental pattern used I ancient Greece, therefore called as Greek Key motif

#Id: 7698

#Unit 1. Molecules and their Interaction Relevant to Biology

                                                     Greek Key Motif

                                                        

#Id: 7699

#Unit 1. Molecules and their Interaction Relevant to Biology

                                                           EF hand motif

#Id: 7701

#Unit 1. Molecules and their Interaction Relevant to Biology

                                                                  Omega loop

Beginning and end of the loop come together

The shape appears similar to Greek Capital Omega

Compact Globular structure

No regular repeating pattern of hydrogen bonds

Side chains pack into the center of the loop

Omega loops have specific functions like

Omega loop from two proteins interact with each other to form dimers

Phosphate binding loop of nucleotide proteins