What is formed in the primary structure of a protein?

In the primary structure of a protein, the sequence of amino acids is established through peptide bonds, which are covalent bonds formed between the carboxyl group of one amino acid and the amino group of another. This process occurs primarily during translation, where ribosomes synthesize proteins based on the sequence of mRNA.

While the answer you've chosen pertains to the interaction of amino acids, the most accurate answer regarding what defines the primary structure is the formation of peptide bonds, which happen specifically when amino acids link together to form a chain. Therefore, the correct answer would emphasize the role of ribosomes in forming these peptide bonds, as they facilitate this reaction during protein synthesis.

It's important to differentiate the various levels of protein structure: the primary structure is solely the linear sequence of amino acids, which is distinctly different from the secondary, tertiary, and quaternary structures that involve various types of bonding and interactions beyond simple amino acid linkage.