Which amino acids are known to contain both nitrogen and oxygen in their side chains?

The correct answer identifies asparagine and glutamine as the amino acids that contain both nitrogen and oxygen in their side chains.

Asparagine has an amide group (–C(=O)NH2) in its side chain, which consists of both a nitrogen atom and a carbonyl (carbon-oxygen double bond), thus providing the oxygen. Similarly, glutamine also has an amide group in its side chain that includes both nitrogen and carbonyl oxygen. This structural characteristic makes asparagine and glutamine unique among the standard amino acids regarding their side chains.

The other options do not meet the criteria: Alanine has a simple hydrocarbon side chain, while cysteine contains a sulfur atom in its side chain. Arginine and lysine have positively charged amine groups in their side chains but lack oxygen. Histidine and tryptophan also fail to include oxygen in their side chains. Therefore, asparagine and glutamine are the only amino acids listed that contain both nitrogen and oxygen in their side chains.