Final answer:
A long chain of amino acids is called a polypeptide or, when sufficiently long, a protein. Proteins fold into specific shapes due to the properties of their constituent amino acids, and their unique sequences determine their specific functions.
Step-by-step explanation:
A long chain of amino acids is called a polypeptide, which consists of amino acid units linked by peptide bonds. When a polypeptide exceeds around 50 amino acids in length, it is typically referred to as a protein. The folding of these chains into specific three-dimensional structures, vital for their function, is driven by the chemical properties of the amino acids themselves, including their tendencies to be attracted or repelled by water and their interactions with each other.
Proteins can have different levels of structure: the primary structure is the unique sequence of amino acids encoded by a gene, the secondary structure involves local folding patterns such as alpha-helices and beta-pleated sheets, the tertiary structure is the overall three-dimensional conformation, and the quaternary structure (if present) is the arrangement of multiple polypeptide chains.