question: What bonding is formed in polar amino acid side chains?
distractor3: helium bonding
distractor1: calcium bonding
distractor2: carbon bonding
correct_answer: hydrogen bonding
support: Hydrogen bonding. Hydrogen bonding forms between a highly electronegative oxygen atom or a nitrogen atom and a hydrogen atom attached to another oxygen atom or a nitrogen atom, such as those found in polar amino acid side chains. Hydrogen bonding (as well as ionic attractions) is extremely important in both the intra- and intermolecular interactions of proteins (part (b) of http://catalog. flatworldknowledge. com/bookhub/reader/2547 - gob-ch18_s04_s01_f05). Disulfide linkages. Two cysteine amino acid units may be brought close together as the protein molecule folds. Subsequent oxidation and linkage of the sulfur atoms in the highly reactive sulfhydryl (SH) groups leads to the formation of cystine (part (c) ofhttp://catalog. flatworldknowledge. com/bookhub/reader/2547 - gob-ch18_s04_s01_f05). Intrachain disulfide linkages are found in many proteins, including insulin (yellow bars in http://catalog. flatworldknowledge. com/bookhub/reader/2547 - gob-ch18_s04_s01_f01) and have a strong stabilizing effect on the tertiary structure.