To Study the effect of Secondary Structure elements on CD spectrum of proteins

1. In biological reactions proteins play a role of a ______________ ?
2. Protein is a polymer. Monomeric unit of which is amino acid. Each amino acid has a chiral center. So is it possible to apply CD spectrum to study the structure of a protein?
3. Having known the primary structure of a protein the main interest of biologists is to know the secondary structure of a protein. How a spectroscopic method can help it?