IB Biology B1.2 Notes

Whilst you now understand the basic structure of proteins and how they form polypeptides via peptide bonds, you know need to understand how these form 3D structures to become mature proteins. This all begins with R-groups, which is the only chemically variable component of the amino acid.

It is this variable group that provides the different amino acids with a host of different properties:

1. Hydrophobic R-groups - in soluble proteins, folded into the protein’s interior. In insoluble proteins, present on the protein's exterior.
2. Hydrophilic R-groups - in soluble proteins are arranged on the exterior of the protein
   1. Polar R-groups - participate in dipole-dipole bonding and hydrogen bonding.
   2. Charged R groups - create electrostatic attractions or repulsions which will influence the ultimate structure, stability and function of the protein.

Some R-groups are pH sensitive and accept or donate protons in accordance with the surrounding pH. This variation in R-groups and its accompanying effect on all potentially different chemical properties facilitates proteins versatility in a host of different functions, to include catalytic, transport, building and signal transduction.