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.
Mammals give live birth to their offspring. Reptiles and amphibians lay eggs. Mammals are also usually warm blooded while reptiles and amphibians are cold blooded. Most amphibians and reptiles abandon their young at a certain age while most mammals will take care of their offspring forever.
