The side chain of serine contains oxygen. water-soluble proteins often contain serine. where would the serine side chain most likely be found in a protein dissolved in water?

Answer;

-On the polar end or the hydrophillic end of the protein.

Explanation;

-Each amino acid has at least one amine and one acid functional group as the name implies. The different properties result from variations in the structures of different R groups.The R group is often referred to as the amino acid side chain.

-Side chains which have various functional groups such as acids, amides, alcohols, and Amines will impart a more polar character to the amino acid. Polar amino acids include serine, threonine, asparagine, glutamine, histidine and tyrosine.

Therefore; serine being a polar or hydrophillic  amino acid will be found on the polar side chain of the protein.

The serine side chain most likely would be found outside of the globular water-soluble protein.

Most proteins have a hydrophobic core (where the hydrophobic amino acids are), and a polar surface in contact with the environment (water). Polar and charged amino acids cover the surface of the molecule and are in contact with a solvent  (water) due to their ability to form hydrogen bonds. Hydroxyl group (-OH) of the serine classifies it as a polar amino acid.