Final answer:
Arginine (Arg) is a conditionally essential amino acid, important for the urea cycle and protein-RNA interactions. Represented by the codons AGA and AGG, it is crucial in the genetic code for protein synthesis.
Step-by-step explanation:
Arginine, often represented by its three-letter code Arg, is a conditionally essential amino acid in protein biosynthesis. Its codons are AGA and AGG, and it plays a pivotal role in the urea cycle, where it is cleaved into ornithine and urea by the enzyme arginase. Arginine is also a significant amino acid within RNA-protein interfaces, providing numerous contacts due to its terminal guanidinium ion, which is planar, aromatic, and positively charged.
This ion's ability to offer a pattern of hydrogen bonding aligns well with the edge of nucleobases, rendering arginine abundant at these sites. Additionally, arginine can bind RNA, such as in L-Arg binding motifs found in certain RNA structures that are important for regulatory interactions. Despite being synthesized in the body, arginine is considered semi-essential as it may not be produced in sufficient quantities, especially for growing children, necessitating dietary intake.