What is the primary structure of a protein?

The primary structure of a protein refers to its unique sequence of amino acids, which are the building blocks of proteins. This specific order of amino acids is crucial because it determines how the protein will fold into its three-dimensional structure, which ultimately dictates its function within the organism.

The sequence of amino acids in the primary structure is encoded by the organism's DNA, and any change in this sequence can lead to significant alterations in the protein's properties and functions. Therefore, understanding the primary structure is essential for grasping the overall biology of proteins, as it lays the foundation for all subsequent levels of protein structure—secondary, tertiary, and quaternary—which involve various types of interactions and foldings.

Focusing on the other choices, the arrangement of nucleotides in DNA pertains to genetic information rather than protein structure. The folding pattern and three-dimensional shape of a protein are related to its higher levels of structure, which result from the primary structure but are not the definition of it.