Organic chmistry question~ ~ ~ ?

Question

The quaternary structure of proteins is

a. the aggregation of distinct protein chains

b. a four-sided protein structure

c. the direction of twisting of the helical structure

d. how hydrogen bonds link each aminoacid in a polypeptide chain to thefourth aminoacid further along

Answer 1

a. the aggregation of distinct protein chains

Answer 2

a.  the aggregation of distinct protein chains.

The quaternary structure is the interaction between several chains of peptide bonds. The individual chains are called subunits. The individual subunits are not necessarily covalently connected, but might be connected by a disulfide bond. Not all proteins have quaternary structure, since they might be functional as monomers. The quaternary structure is stabilized by the same range of interactions as the tertiary structure. Complexes of two or more polypeptides (i.e. multiple subunits) are called multimers. Specifically it would be called a dimer if it contains two subunits, a trimer if it contains three subunits, and a tetramer if it contains four subunits. Multimers made up of identical subunits may be referred to with a prefix of "homo-" (e.g. a homotetramer) and those made up of different subunits may be referred to with a prefix of "hetero-" (e.g. a heterodimer). Tertiary structures vary greatly from one protein to another. They are held together by glycosydic and covalent bonds.