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TLS Online TPP Program

#Id: 7780

A set of seven structural nucleoporins forms a Y-shaped structure about the size of the ribosome, known as the Y complex.

#Unit 2. Cellular Organization #Nucleus #Part B Pointers
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TLS Online TPP Program

#Id: 8462

#Unit 1. Structure and Function of Biomolecules

TLS Online TPP Program

#Id: 8463

#Unit 1. Structure and Function of Biomolecules

Interactions between amino acid residues at the ends of the helical segment and the electric dipole inherent to the  helix.
TLS Online TPP Program

#Id: 8464

#Unit 1. Structure and Function of Biomolecules

The overall effect is a significant net dipole for the a helix that gives a partial positive charge at the amino end and a partial negative charge at the carboxy end of the a helix. 
TLS Online TPP Program

#Id: 8465

#Unit 1. Structure and Function of Biomolecules

The magnitude of this dipole moment corresponds to about 0.5-0.7 unit charge at each end of the helix. These charges would be expected to attract ligands of opposite charge and negatively charged ligands, especially when they contain phosphate groups and frequently bind at the N-termini of a helices. In contrast, positively charged ligands rarely bind at the C-terminus
TLS Online TPP Program

#Id: 8466

#Unit 1. Structure and Function of Biomolecules

Polyleucine and polyalanine readily form a-helical structures.
TLS Online TPP Program

#Id: 8467

#Unit 1. Structure and Function of Biomolecules

polylysine is a random coil at pH values below about 11, where repulsion of positive charges prevents helix formation. At pH 12, where polylysine is a neutral peptide chain, it readily forms an a-helix.