All proteins have primary (1°), secondary (2°) and tertiary (3°) structure. In addition, some (but not all) proteins exhibit quaternary (4°) structure. Explain quaternary structure and why only some proteins exhibit that level of structure.

A mutation leads to a change in amino acid from valine, an amino acid with a nonpolar side chain, to aspartic acid, an amino acid with a polar, negatively-charged side chain. Do you think that the following levels of protein structure change? If so, how and why? If not, why not? Please frame your answer in terms of chemical bonds and interactions. (primary structure, secondary structure, tertiary structure, quartenary structure)

Explain why it is difficult to draw conclusions about the conformational changes of a protein based on a single crystal structure.