Complete the following vocabulary exercise relating to the level of structure in proteins. match the words in the left-hand column with the appropriate blank in the sentences in the right-hand column.
1. tertiary structure is achieved when a protein folds into a compact, three-dimensional shape stabilized by interactions between side-chain r groups of amino acids.
2. quaternary structure is the result of two or more protein subunits assembling to form a larger, biologically active protein complex.
3. primary structure is the sequence of amino acids in a protein.
4. secondary structure describes the alpha-helices and beta-sheets that are formed by hydrogen bonding between backbone atoms located near each other in the polypeptide chain.