The function of the protein is determined by the sequence of the amino acid. The function of protein is determined by its shape, and the shape of the protein is determined by the sequence of nucleotide which is present in the gene which encodes for the protein.
These sequence determine the primary, secondary and tertiary structure of protein which depends mainly on the folding of the protein. And the biological function of the protein such as enzymatic, signalling and structural is determined by these structure.
Example: Each enzyme has a active site where substrate binds in order to carry out reactions. The shape of amino acid depends on the sequence of amino acid and protein folding.
Thus, the structure of amino acid sequence is dependent on the its function.
