Which of the following correctly describes quaternary level of structure in proteins?
A) It is when all the amino acids have joined together with
peptide bonds.
B) It is when the hydrogen bonds have interacted with one
another to form shapes such as alpha-helices and beta-
pleated sheets.
C) It is when functional groups have been added to a protein
in the Golgi apparatus
D) It is when several folded proteins interact with one another
to form a protein complex.
E) It is when side groups on the amino acids have interacted to
fold the protein into a specific three dimensional shape.