1. Mark all TRUE statements: A. protein chains can only consist of either purely hydrophobic or hydrophilic amino acids B. because enzyme active sites are symmetric, the reactions they catalyze are consequently racemic C. all amino acids share common structural features and can be differentiated by their specific R group D. almost all amino acids have two possible stereoisomers E. proteins are composed of a mix of L and D amino acids. ------------------------------------------------------------------------------------------ 2. Mark all TRUE statements about turns and loops A. They allow polypeptide chains to change directions B. They’re generally located in the interior of proteins C. Loops exposed to an aqueous environment are usually composed of hydrophilic amino acids D. Loops are found only on sheets E. They can interact with other proteins and the environment Solution Answer: 1. B. because enzyme active sites are symmetric, the reactions they catalyze are consequently racemic - True C. all amino acids share common structural features and can be differentiated by their specific R group - True D. almost all amino acids have two possible stereoisomers - True. 2. Tursn and Loops; A. They allow polypeptide chains to change directions - True. C. Loops exposed to an aqueous environment are usually composed of hydrophilic amino acids - True. E. They can interact with other proteins and the environment - True..