Final answer:
A chain of 25 amino acids is called a polypeptide, which is a term used for any chain of amino acids linked by peptide bonds. Chains with about 50 or more amino acids are commonly referred to as proteins. The sequence of amino acids determines the protein's function when it folds into its three-dimensional structure. The correct option is 1).
Step-by-step explanation:
A chain of 25 amino acids is called a polypeptide. Amino acids are linked together through peptide bonds to form a polypeptide chain. Additional amino acids can be added to this chain with the formation of more peptide bonds.
In the terminology of biochemistry, a molecule consisting of two amino acids is referred to as a dipeptide, and one with three amino acids is called a tripeptide. Chains longer than a few amino acids are referred to as peptides or polypeptides, while those with about 50 amino acids or more are commonly called proteins or polypeptides as well.
In a physiological context, a polypeptide must fold into a specific three-dimensional structure to be considered a functionally active protein.
Proteins can be composed of one or multiple polypeptide chains, and the sequence in which the amino acids are connected plays a critical role in determining the protein's function. Option 1) is the correct one.