Protein subunits in a multi-subunit protein are held to each other primarily by

a) hydrophobic interactions exclusively
b) both strong and weak interactions
c) covalent bonds
d) hydrophobic and other weak interactions

D

Explanation:

A multi-subunit protein is a good example of a quaternary-structure protein. A quaternary structure protein is often defined as a unit composed of different polypeptide sequences or chains (often called subunits). The most common interactions observed in these conformations are chemical interaction between the “R” groups in the amino acids that composed the proteins. These interactions are mostly weak interactions (such as London dispersion forces and hydrogen bonds). Therefore, option D is correct.  

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