Which row gives the correct statement about protein structure?
- Aprimary: determined by the sequence of DNA nucleotides; secondary: occurs by hydrogen bonding between NH and C=O groups of amino acids; tertiary: disulfide, ionic, hydrogen bonds and hydrophobic interactions are all involved; quaternary: always formed by association of two or more polypeptides
- Bprimary: the number of amino acids in each polypeptide chain; secondary: in a single polypeptide it is either an $\alpha$-helix or a $\beta$-pleated sheet; tertiary: the bonds are formed at specific points determined by the primary structure; quaternary: always formed by two or more polypeptides held together by bonds formed between the polypeptides
- Cprimary: formed by twenty different amino acids linked in a specific order; secondary: an $\alpha$-helix is formed by hydrogen bonds between side chains of amino acids; tertiary: only globular proteins have this level of structure; quaternary: always formed by two or more different polypeptides to give the final shape
- Dprimary: the sequence of amino acids in each polypeptide chain; secondary: a $\beta$-pleated sheet is the result of a folded polypeptide forming hydrogen bonds between adjacent strands; tertiary: reactions between side chains of specific amino acids give a specific 3-D shape; quaternary: always formed by two or more polypeptides and a metal ion