Upon absorbing UV-B photons, the tryptophans undergo structural changes that break the salt bridges, leading to the dissociation of the two functionally active monomers. The monomers then interact with COP1–SPA complexes to activate gene expression

TLS Online TPP Program

#Id: 8757

#Unit 1. Molecules and their Interaction Relevant to Biology

A fully folded 100-residue protein is only about 40 kJ ∙ mol−1 more stable than its unfolded form (for comparison, the energy required to break a typical hydrogen bond is ∼20 kJ ∙ mol−1).

TLS Online TPP Program

#Id: 8758

#Unit 1. Molecules and their Interaction Relevant to Biology

The combined hydrophobic and hydrophilic tendencies of individual amino acid residues in proteins can be expressed as hydropathies. The greater a side chain’s hydropathy, the more likely it is to occupy the interior of a protein.

TLS Online TPP Program

#Id: 8759

#Unit 1. Molecules and their Interaction Relevant to Biology

Hydrogen bonds, which are central features of protein structures, make only minor contributions to protein stability.

TLS Online TPP Program

#Id: 8760

#Unit 1. Molecules and their Interaction Relevant to Biology

This is because hydrogen-bonding groups in an unfolded protein form hydrogen bonds with water molecules. Thus the contribution of a hydrogen bond to the stability of a native protein is the small difference in hydrogen bonding free energies between the native and unfolded states (−2 to 8 kJ ∙ mol−1)

TLS Online TPP Program

#Id: 8761

#Unit 1. Molecules and their Interaction Relevant to Biology

The Hydrophobic Effect Has the Greatest Influence on Protein Stability. The hydrophobic effect, which causes nonpolar substances to minimize their contacts with water, is the major determinant of native protein structure.

TLS Online TPP Program

#Id: 8762

#Unit 1. Molecules and their Interaction Relevant to Biology

Thermostable proteins have such a high incidence of salt bridges.