Although all protein structures are unique, there are common structural building blocks that are referred to as regular secondary structures. some have alpha helices, some have beta sheets, and still others have a combination of both. what makes it possible for proteins to have these common structural elements?

Hydrogen bonds across their molecules.

Explanation:

Proteins can be defined as large molecules which consist of one or more chains of amino acid. Proteins perform a whole lot of functions within an organism and they are include; enzymes for catalysing metabolic reactions, DNA replication, in structuring cells and transport molecules from one location to another. Proteins differ from one another due to their sequence of amino acids which is governed by the nucleotide acids (DNA and RNA) which usually results in protein folding into a specific three-dimensional structure. There are 2 types of this three-dimensional structure of protein and they are:

1. Alpha helical structure: Amino acids vary in their ability to form secondary structure elements. Not all amino acids promote regularity, Proline and glycine are sometimes known as "helix breakers" because they interrupt the regularity an alpha helical conformation. Amino acids that promote this helical conformations are glutamate, lycine, methionine, alanine etc.

2. Beta pleated structure: They form a syretch of polypeptides and they are held hy 2 or 3 hydrogen bonds.