Which row correctly describes the structure of proteins?
- Aprimary structure is the number of amino acids present in a protein; secondary structure is the right-handed spiral formed by the primary structure; tertiary structure is the result of cross-bonding between specific amino acids in the primary structure; quaternary structure is the sub-unit polypeptides that link together to form a protein
- Bprimary structure is the order of amino acids present in a protein encoded by DNA; secondary structure is the coiling of a chain of amino acids to form a $\beta$-pleated sheet or an $\alpha$-helix; tertiary structure is the shape formed by the folding of a polypeptide and is held together by hydrogen bonds; quaternary structure contains two types of polypeptide that interact forming the shape of a protein
- Cprimary structure is the result of translation of an mRNA molecule by a ribosome into a chain of amino acids; secondary structure occurs because of an attraction between hydrogen and oxygen atoms in the peptide bonds; tertiary structure is the result of ionic and hydrogen bonds, disulfide bridges and hydrophobic interactions between amino acids; quaternary structure is formed by four polypeptides and an additional reactive group attached to the protein
- Dprimary structure is the sequence of amino acids in a protein coded by an mRNA molecule; secondary structure is formed by hydrogen bonding between amino acids forming the primary structure; tertiary structure is formed as a result of interaction of the side chains of amino acids in the primary structure; quaternary structure is formed by the linking together of more than one polypeptide to form a protein