It is strictly recommended to use the words "amino acid residues" when discussing proteins because when a peptide bond is formed, a water molecule is lost, and therefore proteins are made up of amino acid residues.
Post-translational modification such as phosphorylations and glycosylations are usually also considered a part of the primary structure, and cannot be read from the gene.
Tertiary structure refers to the three-dimensional structure of monomeric and multimeric protein molecules.
The α-helixes and β-pleated-sheets are folded into a compact globular structure.
They should not be confused with random coil, an unfolded polypeptide chain lacking any fixed three-dimensional structure.
Several sequential secondary structures may form a "supersecondary unit".The sequence of amino acids in insulin was discovered by Frederick Sanger, establishing that proteins have defining amino acid sequences.The sequence of a protein is unique to that protein, and defines the structure and function of the protein.These secondary structures are defined by patterns of hydrogen bonds between the main-chain peptide groups.They have a regular geometry, being constrained to specific values of the dihedral angles ψ and φ on the Ramachandran plot.The primary structure of a protein refers to the sequence of amino acids in the polypeptide chain.The primary structure is held together by peptide bonds that are made during the process of protein biosynthesis.Secondary structure refers to highly regular local sub-structures on the actual polypeptide backbone chain.Two main types of secondary structure, the α-helix and the β-strand or β-sheets, were suggested in 1951 by Linus Pauling et al.Very large aggregates can be formed from protein subunits.For example, many thousands of actin molecules assemble into a microfilament.