Answer:
Shape
Step-by-step explanation:
Proteins are made up of amino acids. The amino acid sequence in a protein is determined by the nucleotide sequence present in the DNA of the cell. These amino acids join together and makes the primary structure of protein which fold by making hydrogen bonding and determines the shape of the protein.
The shape of the protein determines the function of that protein. If the shape and structure of the protein gets destroyed then the protein will lose its function. Change in pH, temperature, salt concentration, etc can change the shape of protein and make it functionally inactive.