you are attempting to document the structures of a newly discovered type of protein in your lab. you take them out of storage and allow them to
heat up to 37 c. you notice 4 polypeptide chains each coiled into a 3-d structure. what level of structure are the proteins in?
a. tertiary
b. quaternary
c. secondary
d. primary

B. Quaternary

Explanation:

This is a quaternary structure. A quaternary protein unlike other protein structures like primary, secondary and tertiary is made up of 2 or more polypeptide chains.  Primary, secondary and tertiary protein structures on the other hand are made up of only single polypeptide chain, the only difference in these protein structures is of their interactions.

While synthesizing protein, the very first level is primary structure in which amino acids (monomers) are simply bonded through peptide bond to form a polypeptide (polymer). Then after next level is secondary structure in which amino acids within the polypeptide chain interact through hydrogen bonds with other local amino acids which are located nearby . After secondary level, the next level is tertiary level in which the polypeptide folds even more with the help of various interactions like ionic bonds, covalent bonds and hydrophobic bonds. The interactions in tertiary structures are known as global interactions which means that amino acids can even interact with other amino acids which are distantly located within the same polypeptide chain. When 2 or more such polypeptide chains which already have primary, secondary and tertiary levels coil with each other a quaternary protein is formed.

Quaternary protein level protein is the only one which is in functional form and can perform actual function in our body. Primary, secondary and tertiary levels are non-functional forms of protein.

37⁰C is our normal body temperature in which our proteins exist in their actual form i.e. neither they are denatured nor they are inactive. So, this is a quaternary structure.