Twin and Siamois encode homeodomain transcription factors and are expressed in the organizer

TLS Online TPP Program

#Id: 8459

#Unit 1. Molecules and their Interaction Relevant to Biology

Five types of constraints affect the stability of an  helix: 

(1) the intrinsic propensity of an amino acid residue to form an  helix; 

(2) the interactions between R groups, particularly those spaced three (or four) residues apart; 

(3) the bulkiness of adjacent R groups; 

(4) the occurrence of Pro and Gly residues; and 

(5) 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: 8460

#Unit 1. Molecules and their Interaction Relevant to Biology

The intrinsic propensity of an amino acid residue to form an  helix

TLS Online TPP Program

#Id: 8461

#Unit 1. Molecules and their Interaction Relevant to Biology

The interactions between R groups, particularly those spaced three (or four) residues apart; The assembly is said to have a coiled coil structure because each α helix itself follows a helical path.

TLS Online TPP Program

#Id: 8462

#Unit 1. Molecules and their Interaction Relevant to Biology

TLS Online TPP Program

#Id: 8463

#Unit 1. Molecules and their Interaction Relevant to Biology

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. Molecules and their Interaction Relevant to Biology

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.